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Some thoughts for the writers of CI boiler installation manuals

hot_rod
hot_rod Member Posts: 18,279
Looking over a common IO manual, dated 2022 last evening.

Showing a high efficiency air separator would improve the air and O2 removal, quite possibly improve the boiler and heat emitter efficiency. Good chance of extending the boiler life.

In addition to P/S piping options show a hydraulic separator with multi function as an option. Which would also improve air, dirt and magnetic performance.

Consider showing a viable variable speed return protection piping or modules. The variable speed bypass circ improperly applied, will not, cannot assure 100% return temperature protection. There is no way to disconnect the load from the boiler. An expensive swing and a miss :)

Consider this CI boiler on a gravity conversion application shown below. Return from the radiators on start up, any call for heat really may be room temperature, or colder if piping is in an unheated basement or crawlspace.

Call it 70° return from the system. Running balls out, a properly sized boiler can maybe lift that temperature in the boiler 20°, although doubtful with that thermal mass load. Call the boiler supply 90°. Maybe by some act of God it raises it 40° to 110°

So how does 90° degree, or 110° with heavenly intervention, boiler supply mix with 70° return from the radiators to get a 130° return? The numbers don't add up, pun intended. That boiler will run for hours to catch a high mass load, CI radiators, radiant slabs.

A simple thermostatic return valve is 100% solution.

A very simple piping modification, same temperature controlled VS circulator would get you 100% return protection.

Judging by the number of failed, condensation corroded, young CI boilers that come across this list... Think of the warranty money that could be saved. Or the unfortunate conversation of denying a warranty on a corroded boiler that was inadequately protected.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
Long Beach EdMad Dog_2SuperTech

Comments

  • clammy
    clammy Member Posts: 2,832
    As great as it would be if they included all that information to aide for those installing boiler where theses issues would occur or have occurred ,but you may lead a horse to water it doesn’t mean it will drink . The same can be seen and read in the steam boilers manuals showing proper piping of there product and yet guys still get it wrong even w a stick drawings .
    I would hope that the ones who do come across these problems would be familiar enough with what they are seeing and have enough brain btus to correct it properly . But in playing the devils advocate it’s usually those who may be in the business but truely don’t see the whole picture and understand cause and effect and add in time . Precaution is some times stated as recreating the wheel and most don’t like that kind of talk because it means$ but they pay one way or another .
    Great thoughts for the real world out there
    Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,169
    Agree with @clammy. They don't read the steam manuals so I doubt they will read the hW ones but good ideas @Hotrod .

    Maybe a mandatory reading class would work.

    I know early in my career I read everything I could get my hands on. The older I got ....not so much as the manuals got thicker & thicker.

    But I read enough to keep myself out of trouble. Doing things twice doesn't work for me
    Long Beach Ed
  • hot_rod
    hot_rod Member Posts: 18,279

    Agree with @clammy. They don't read the steam manuals so I doubt they will read the hW ones but good ideas @Hotrod .

    Maybe a mandatory reading class would work.

    I know early in my career I read everything I could get my hands on. The older I got ....not so much as the manuals got thicker & thicker.

    But I read enough to keep myself out of trouble. Doing things twice doesn't work for me

    The correct piping info should be in the manual for those who do read it. I can’t help those that don’t want to be helped, those that will not read the manual.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    GGrossknotgrumpyEdTheHeaterMan
  • gmcinnes
    gmcinnes Member Posts: 107
    That's an interesting idea @hot_rod.

    I have a thread way back from when my boiler was installed discussing the merits of the boiler (system?) bypass that was installed (almost) per the I/O manual, and whether it was adequate.

    I have a high mass CI system, and my concerns were the ones you outlined above. And the water temps you're being generous with above are more favorable than mine. I decided to let the bypass system ride for a few years and see if there were any signs of corrosion. After 5 years, do you understand why not? I don't.

    FWIW it's Burnham MPO-IQ and it's supposed to have some technology that prevents these issues, but I've never found a good explanation.

    OTOH I'm not sure I want to see the top of my chimney liner. :) If it does become an issue, your solution looks like a simpler mitigation.
  • Mad Dog_2
    Mad Dog_2 Member Posts: 3,942
    Me thinks, no matter what we all do to edify the ignorant, few will really heed the advice. Many plumbers don't like to read, period! They'll glance at a sketch quickly and do their best to duplicate it, often missing the key takeaways .   If we're lucky, they'll grasp the life safety issues of a boiler and that's a good thing.  Well keep trying...Mad 🐕 Dog
    Long Beach Edgmcinnes
  • hot_rod
    hot_rod Member Posts: 18,279
    Why not put accurate information in the manual for those that do read it and want to learn how to give the customer the full benefit of their purchases?

    If they spend an extra XXX dollars to be assured their boiler is always protected, why not provide that? A manufacturer went to the trouble and expense to provide the protection add on option.

    I go to the store buy a nice variable speed drill to cover all my drilling needs. I get home and it only operates at one speed. The manufacturer tells me most people only use one speed, so we didn’t include all the extra speeds. Most people don’t read the box.

    Is that on me or them?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    GGrossknotgrumpy
  • Mad Dog_2
    Mad Dog_2 Member Posts: 3,942
    I find most manuals and instructions lacking. The ones I prefer are VERY visual and reflect actual real life and trade symbols.  Like, writing, I try to make it clear and simple enough so that the simplest person in the room can understand but with enough detail to reach the more experienced and knowledgeable folks. Mad Dog 🐕 
    Larry Weingarten
  • hot_rod
    hot_rod Member Posts: 18,279
    Hard to believe anyone could program a new mod con boiler without reading the manual??

    Venting options on the first 20 pages of manuals probably bore most readers from continuing.

    Put the piping options, clearly and accurately drawn first!
    Put some color to them for the visual learners. Most installers understand what red and blue indicates.

    Weil McLain had some excellent, accurate piping drawings back in their radiant days. They hired it out.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    gmcinnesGGrossMad Dog_2
  • Paul Pollets
    Paul Pollets Member Posts: 3,573
    I started using Viessmann products over 30 years ago. Their manuals were very specific as to correct piping schematics for each possible application. And the controls were not a mystery to wire because the manual was specific. Most manufacturers were very slow to provide correct piping diagrams, and most technicians were hesitant to read and follow.
    GGrossMad Dog_2
  • WMno57
    WMno57 Member Posts: 669
    edited January 27
    gmcinnes said:

    I have a high mass CI system, and my concerns were the ones you outlined above. And the water temps you're being generous with above are more favorable than mine. I decided to let the bypass system ride for a few years and see if there were any signs of corrosion. After 5 years, do you understand why not? I don't.

    Old CI boilers got away with this at the expense of efficiency. My 70 YO boiler is not Pri/Sec. Burner is not atmospheric (forced induction?), and warm start. Aquastat and Thermostat are completely independent. I spend hundreds on methane to save thousands on Labor and Chinese chips.
    Mad Dog_2
  • EricPeterson
    EricPeterson Member Posts: 115
    hot_rod said:

    Looking over a common IO manual, dated 2022 last evening.

    Showing a high efficiency air separator would improve the air and O2 removal, quite possibly improve the boiler and heat emitter efficiency. Good chance of extending the boiler life.

    In addition to P/S piping options show a hydraulic separator with multi function as an option. Which would also improve air, dirt and magnetic performance.

    Consider showing a viable variable speed return protection piping or modules. The variable speed bypass circ improperly applied, will not, cannot assure 100% return temperature protection. There is no way to disconnect the load from the boiler. An expensive swing and a miss :)

    Consider this CI boiler on a gravity conversion application shown below. Return from the radiators on start up, any call for heat really may be room temperature, or colder if piping is in an unheated basement or crawlspace.

    Call it 70° return from the system. Running balls out, a properly sized boiler can maybe lift that temperature in the boiler 20°, although doubtful with that thermal mass load. Call the boiler supply 90°. Maybe by some act of God it raises it 40° to 110°

    So how does 90° degree, or 110° with heavenly intervention, boiler supply mix with 70° return from the radiators to get a 130° return? The numbers don't add up, pun intended. That boiler will run for hours to catch a high mass load, CI radiators, radiant slabs.

    A simple thermostatic return valve is 100% solution.

    A very simple piping modification, same temperature controlled VS circulator would get you 100% return protection.

    Judging by the number of failed, condensation corroded, young CI boilers that come across this list... Think of the warranty money that could be saved. Or the unfortunate conversation of denying a warranty on a corroded boiler that was inadequately protected.

    As a homeowner/installer I agree 100% with this sentiment, as I found the documentation that came with my boiler wholly inadequate in terms of providing a simple straightforward recommendation for boiler protection.

    At the risk of repeating myself as I've posted about this in the past, my house is a converted gravity hot water system with CI radiators, one circulator / three zones, TRVs, and a Burnham ES2 boiler. Very simple and straightforward. It's worked fine for 10 years with a system bypass valve but this has always bothered me that I have a sub-optimal solution in place.

    @hot_rod and others have provided lots of valuable information about ways to deal with this issue.
    What's held me back so far is that I want to avoid a complicated setup with multiple points of failure.
    I've been mining the Wall for years collecting information so that I can put in place an optimal solution, but every year I put it off. Maybe 2023 is the year. Or I find a contractor that I can work with in my area.

    Thanks,
    Eric Peterson



    gmcinnes
  • GGross
    GGross Member Posts: 412
    @Paul Pollets

    Agree with you there, so many things that Viessmann did first and took flak for you see other manufacturers copy now. Not approving PVC, primary secondary piping, pushing a hydro separator. And they have application guides for every model boiler in full color with dozens of different system examples and layouts, complete with wiring diagrams for each specific application. I recently looked for some examples for another brand boiler I sell and was very disappointed how other manufacturers handle the "application guide"
    Mad Dog_2
  • Waher
    Waher Member Posts: 100
    edited January 27
    The way to make manuals is take individuals that know nothing about anything and give them the manual and interview them. Every question they ask, provide a diagram (picture of the screw actual size, the tool needed actual size, how each part slips together in sequence, what each term means, etc.). Then give the revised manual to another know nothing, repeat the process. Eventually you'll have a thick manual that even the densest turnip that fell off a truck will be able to understand without having to ask questions.

    I forget which company used to do this with their technical manuals and 1950s housewives. It was their way of creating nearly fool-proof service manuals because almost every question was answered visually in a clear comic book like fashion.
    Mad Dog_2
  • gmcinnes
    gmcinnes Member Posts: 107
    Speaking as a turnip, I approve this comment.
    WaherPC7060Mad Dog_2
  • Lance
    Lance Member Posts: 242
    THERE IS no SUBSTITUTE for a proper education. You will know when you have learned your trade when you start correcting the teachers, start writing your own manuals and start teaching others. Otherwise, we all have to stay in the school of life until we can learn no more. When they engineered the human lifespan to 100 years, they lost the best production in years beyond 100. Just when we get smart enough, we all seem to die. All that is left is what we taught and wrote. Thanks to all for sharing. Its why I teach those who are young and smart enough to learn.
    GGrossMad Dog_2
  • Hoagie
    Hoagie Member Posts: 4
    Couple of suggestions - Hydrolevel Hydrostats have a circulator hold-off feature that is effective in minimizing flue gas condensation, such as caused by converted gravity systems. It won't send power to C1 until the supply temp reaches 125º, and has a 10º differential so that if a second cold zone comes on and drops the temp below 115º, the circulator power goes off again.

    For multi-zone panels, you can run BX from C1 to ZC on the zone relay panel and remove the jumper from ZC. On a call from any tstat, the zone circ has to wait until the boiler is up to temp.

    The old-timers trick, which is not as elegant as Hot Rod's thermostatic bypass, is a piping bypass from the supply to the return with a ball valve. Below is a diagram from the Peerless® Color of Water 2.0.

    The version 2.0 of Color of Water is a 76 page full-color manual that includes primary/secondary, hydraulic separators, buffer tanks, explanations of boiler system components, piping diagrams, etc.

    You can buy a hard copy for 10 bucks (they're expensive to print,) but you can download an electronic copy for free at PeerlessBoilers.com. You will have to register for a password because we're trying to keep homeowners from hurting themselves by doing their own service.

    Peerless® Hydronic System training classes include a free hard copy, and classes are held at the Boyertown, PA factory as well as with our Road Show Live-Fire training trailer. You can sign up for a class or request a class in your area once you have a website password.

    Training is a win-win, but everyone is so busy that it isn't easy to get away or to send new techs, even as much as it would help. Online webinars and short training videos on essential subjects are also available on the training section of PeerlessBoilers.com.
    Mad Dog_2
  • Paul Pollets
    Paul Pollets Member Posts: 3,573
    It costs money to produce a well written manual. With modern CAD diagrams, it's easy to show the correct piping strategies. And control strategies. Caleffi has done a wonderful job and their info is easily accessed. At one point, John Seigenthaler was doing schematics for several companies. If the manuals were as specific as Viessmann's, more systems would be installed correctly. They never tell you the pipe sizes(unless it's steam) ...if you don't get that right, expect problems.
    There's a need to spend more time on the business than in the business turning wrenches. It requires a complete understanding of how to maximize a system's efficiency, and make a profit while doing so. A good manual minimizes errors and mistakes cost money. And the contractor has to read them.
    GGrossMad Dog_2
  • The Steam Whisperer
    The Steam Whisperer Member Posts: 1,090
    gmcinnes said:

    That's an interesting idea @hot_rod.

    I have a thread way back from when my boiler was installed discussing the merits of the boiler (system?) bypass that was installed (almost) per the I/O manual, and whether it was adequate.

    I have a high mass CI system, and my concerns were the ones you outlined above. And the water temps you're being generous with above are more favorable than mine. I decided to let the bypass system ride for a few years and see if there were any signs of corrosion. After 5 years, do you understand why not? I don't.

    FWIW it's Burnham MPO-IQ and it's supposed to have some technology that prevents these issues, but I've never found a good explanation.

    OTOH I'm not sure I want to see the top of my chimney liner. :) If it does become an issue, your solution looks like a simpler mitigation.

    If you look at the complete heating cycle, you will see why the simple boiler or system bypass works for low temp and/or high mass systems.
    If you start by thinking about the typical low mass fin tube baseboard system, you also will be starting at room temperature or near room temperature water each time. I don't think I have ever seen any return temperature protection recommended for this type of system (unless multi-zone or extreme setbacks). When this system starts, the boiler will run at condensing temperatures probably for several minutes as the boiler temperature rises (in this case along with the system). Now on a high mass system, using bypass piping partially decouples the boiler from the system, so the boiler temperature can rise much more quickly than the system temperature.
    In a high mass system, when starting with a cold boiler and cold system and the pump begins moving water across the boiler, with a system bypass only a small amount of water is pumped into the system. Most of the water is pumped back into the boiler return. Since there is very little temperature difference between the boiler and the system almost no heat is transferred to the system in this small flow of water… nearly all of it goes back into the return of the boiler. As the boiler warms up, the temperature differential between the boiler and system will increase to a few degrees and a little bit more heat is transferred to the system, with most of the boiler heat continuing to go back into the boiler. As the boiler steadily comes up to temperature, the amount of heat transferred from the boiler loop to the system loop will slowly increase. A fixed “injection” flow rate between the boiler with a steadily increasing delta tee will gradually increase the amount of heat transfer to the system. As the boiler gets hotter, a larger and larger amount of heat is transferred. By setting the flow rates carefully with a fixed bypass, the boiler can get up to temperature in a reasonable amount of time, just like it does with a low mass fin tube baseboard system, essentially mirroring boiler operating temperatures of a cast iron boiler in a low mass system. With many high mass, converted gravity systems you have the additional advantage that for most of the heating season, the system is not at room temperature, but well above room temperature, so the return temperature from the system is much higher than a low mass fin tube system.
    However, this is only part of the picture. The other part is quite clearly demonstrated by the operational cycle of cast iron condensing design boilers. When the heating cycle ends, the pump needs to be shut off at the same time as the boiler flame. Upon shut off, the cast iron boiler heat soaks and drives up the average boiler temperature as the heat in the castings is transferred to the water but is no longer removed by water flow. This extra heat distributes through the boiler and increases the temperature of the lower portion of the castings that may have been operating in the condensing range and dries out the castings, so very little corrosion occurs. Anyone that has worked with the Weil McLain CG series boiler, a very low water content cast iron boiler, will likely be very familiar with this phenomenon…. When these boilers end a firing cycle and the pump shuts off at the same time after running at high temperatures, the water in the boiler will often begin to boil even under the higher pressures in a closed system. These boilers do particularly well in converted gravity systems often without any bypass piping and have little corrosion.

    A boiler bypass set up works similarly. A high delta tee is created across the boiler, but at very low flows, so the average boiler temperature can rise much more quickly than the system temperature. Upon end of the firing cycle and with the pump shutting down, the same heat soak process occurs to dry out the castings, if need be.
    I have found on my own converted gravity system using boiler bypass piping that having the pump shut down is critical to making sure that the heat soak/ drying cycle occurs. I spent one heating season with the pump running continuously to help improve heating during remodeling, and most of the pins at the bottom of the boiler completely corroded off. I learned my lesson and the pump is always cycled now.
    Also, of importance to this discussion is the combustion efficiency of the boiler. I am fortunate to have one of the early 1990’s transitional design atmospheric gas boilers that have much denser pinning on the heat exchanger and still have the older, much more efficiently burning cast iron burners. The combustion numbers for this boiler are at about 20 To 30% excess air (higher co2 numbers) along with increased heat transfer of a modern heat exchanger. All newer atmospheric boilers I’ve tested, except the Dunkirk 249 series, run about 50% excess air, which decreases the condensation temperature of the boiler. Most new atmospherics probably don’t have any condensation issues until return water is between 110 and 120F, especially since the temperature of the casting on the flame side is much higher than the water temperature side.
    I have another atmospheric cast iron boiler rated at 150,000 btu/hr input that heats about a 5000 sq ft 1950’s 1 inch steel pipe in concrete slab radiant floor. This boiler is piped with a system bypass with a P/S loop going out to the system. This system probably never sees return temperatures above 85F, even in the coldest weather and the boiler has no corrosion issues. The floors never even feel warm, just not cold.


    To learn more about this professional, click here to visit their ad in Find A Contractor.
    Mad Dog_2
  • hot_rod
    hot_rod Member Posts: 18,279

    gmcinnes said:

    That's an interesting idea @hot_rod.

    I have a thread way back from when my boiler was installed discussing the merits of the boiler (system?) bypass that was installed (almost) per the I/O manual, and whether it was adequate.

    I have a high mass CI system, and my concerns were the ones you outlined above. And the water temps you're being generous with above are more favorable than mine. I decided to let the bypass system ride for a few years and see if there were any signs of corrosion. After 5 years, do you understand why not? I don't.

    FWIW it's Burnham MPO-IQ and it's supposed to have some technology that prevents these issues, but I've never found a good explanation.

    OTOH I'm not sure I want to see the top of my chimney liner. :) If it does become an issue, your solution looks like a simpler mitigation.

    If you look at the complete heating cycle, you will see why the simple boiler or system bypass works for low temp and/or high mass systems.
    If you start by thinking about the typical low mass fin tube baseboard system, you also will be starting at room temperature or near room temperature water each time. I don't think I have ever seen any return temperature protection recommended for this type of system (unless multi-zone or extreme setbacks). When this system starts, the boiler will run at condensing temperatures probably for several minutes as the boiler temperature rises (in this case along with the system). Now on a high mass system, using bypass piping partially decouples the boiler from the system, so the boiler temperature can rise much more quickly than the system temperature.
    In a high mass system, when starting with a cold boiler and cold system and the pump begins moving water across the boiler, with a system bypass only a small amount of water is pumped into the system. Most of the water is pumped back into the boiler return. Since there is very little temperature difference between the boiler and the system almost no heat is transferred to the system in this small flow of water… nearly all of it goes back into the return of the boiler. As the boiler warms up, the temperature differential between the boiler and system will increase to a few degrees and a little bit more heat is transferred to the system, with most of the boiler heat continuing to go back into the boiler. As the boiler steadily comes up to temperature, the amount of heat transferred from the boiler loop to the system loop will slowly increase. A fixed “injection” flow rate between the boiler with a steadily increasing delta tee will gradually increase the amount of heat transfer to the system. As the boiler gets hotter, a larger and larger amount of heat is transferred. By setting the flow rates carefully with a fixed bypass, the boiler can get up to temperature in a reasonable amount of time, just like it does with a low mass fin tube baseboard system, essentially mirroring boiler operating temperatures of a cast iron boiler in a low mass system. With many high mass, converted gravity systems you have the additional advantage that for most of the heating season, the system is not at room temperature, but well above room temperature, so the return temperature from the system is much higher than a low mass fin tube system.
    However, this is only part of the picture. The other part is quite clearly demonstrated by the operational cycle of cast iron condensing design boilers. When the heating cycle ends, the pump needs to be shut off at the same time as the boiler flame. Upon shut off, the cast iron boiler heat soaks and drives up the average boiler temperature as the heat in the castings is transferred to the water but is no longer removed by water flow. This extra heat distributes through the boiler and increases the temperature of the lower portion of the castings that may have been operating in the condensing range and dries out the castings, so very little corrosion occurs. Anyone that has worked with the Weil McLain CG series boiler, a very low water content cast iron boiler, will likely be very familiar with this phenomenon…. When these boilers end a firing cycle and the pump shuts off at the same time after running at high temperatures, the water in the boiler will often begin to boil even under the higher pressures in a closed system. These boilers do particularly well in converted gravity systems often without any bypass piping and have little corrosion.

    A boiler bypass set up works similarly. A high delta tee is created across the boiler, but at very low flows, so the average boiler temperature can rise much more quickly than the system temperature. Upon end of the firing cycle and with the pump shutting down, the same heat soak process occurs to dry out the castings, if need be.
    I have found on my own converted gravity system using boiler bypass piping that having the pump shut down is critical to making sure that the heat soak/ drying cycle occurs. I spent one heating season with the pump running continuously to help improve heating during remodeling, and most of the pins at the bottom of the boiler completely corroded off. I learned my lesson and the pump is always cycled now.
    Also, of importance to this discussion is the combustion efficiency of the boiler. I am fortunate to have one of the early 1990’s transitional design atmospheric gas boilers that have much denser pinning on the heat exchanger and still have the older, much more efficiently burning cast iron burners. The combustion numbers for this boiler are at about 20 To 30% excess air (higher co2 numbers) along with increased heat transfer of a modern heat exchanger. All newer atmospheric boilers I’ve tested, except the Dunkirk 249 series, run about 50% excess air, which decreases the condensation temperature of the boiler. Most new atmospherics probably don’t have any condensation issues until return water is between 110 and 120F, especially since the temperature of the casting on the flame side is much higher than the water temperature side.
    I have another atmospheric cast iron boiler rated at 150,000 btu/hr input that heats about a 5000 sq ft 1950’s 1 inch steel pipe in concrete slab radiant floor. This boiler is piped with a system bypass with a P/S loop going out to the system. This system probably never sees return temperatures above 85F, even in the coldest weather and the boiler has no corrosion issues. The floors never even feel warm, just not cold.


    So how does most of the flow go back to the boiler when it is cold, but less and less as it heats?
    With a valve in a fixed position?

    A famous, industry trainer taught me, whatever goes into a tee, a fitting, must come out of a tee or fitting

    Sounds to me like shutting the pump off at the end of the cycle is protecting more then the fixed bypass.
    What is the gpm flow rate of the boiler pump? Somehow it moves the full capacity of what the boiler can accomplish to heat your home at some point in the cycle ?

    While I'm sure various means of bypass can work on different systems,to some degree, by design or more likely by shear luck since there is no published data on how, when and if to set the bypass at 30, 60, or 90%

    If you set your bypass at 90% get a high delta, warm the boiler, it cannot be supplying more then 10% to the system? Either now, or later. What goes into a tee, etc...
    Regardless if the boiler is cool or 180F hot. A zoned system would complicate this further, as flow demand changes.

    Hard to argue with the simplicity of coolant thermostats used in auto engines, TRV, Mix valves and protection devices. Wax or liquid based temperature sensing and response.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    knotgrumpyMad Dog_2
  • xmorganx
    xmorganx Member Posts: 21
    RTFM is the absolute first thing I teach my apprentices. While I agree that the piping diagram shown is a bit lacking, I have seen far far worse. I like the Lochinvar manuals. The IBC ones just confirm that they're control people and don't really get piping. They are supposed to be concept drawings- not a replacement for training and experience...
    If you have ever had the misfortune of having to do the gas piping for a furnace, you must fully appreciate the comparative clarity and detail in any boiler manual. Just for fun, tomorrow I'll send you a few screenshots of the manual for an ATW (bought by client) that I'm installing. Do you know what an octopus plug is? I don't, but they are apparently not permitted. It's a gem, truly.
    Mad Dog_2
  • The Steam Whisperer
    The Steam Whisperer Member Posts: 1,090
    hot_rod said:

    gmcinnes said:

    That's an interesting idea @hot_rod.

    I have a thread way back from when my boiler was installed discussing the merits of the boiler (system?) bypass that was installed (almost) per the I/O manual, and whether it was adequate.

    I have a high mass CI system, and my concerns were the ones you outlined above. And the water temps you're being generous with above are more favorable than mine. I decided to let the bypass system ride for a few years and see if there were any signs of corrosion. After 5 years, do you understand why not? I don't.

    FWIW it's Burnham MPO-IQ and it's supposed to have some technology that prevents these issues, but I've never found a good explanation.

    OTOH I'm not sure I want to see the top of my chimney liner. :) If it does become an issue, your solution looks like a simpler mitigation.

    If you look at the complete heating cycle, you will see why the simple boiler or system bypass works for low temp and/or high mass systems.
    If you start by thinking about the typical low mass fin tube baseboard system, you also will be starting at room temperature or near room temperature water each time. I don't think I have ever seen any return temperature protection recommended for this type of system (unless multi-zone or extreme setbacks). When this system starts, the boiler will run at condensing temperatures probably for several minutes as the boiler temperature rises (in this case along with the system). Now on a high mass system, using bypass piping partially decouples the boiler from the system, so the boiler temperature can rise much more quickly than the system temperature.
    In a high mass system, when starting with a cold boiler and cold system and the pump begins moving water across the boiler, with a system bypass only a small amount of water is pumped into the system. Most of the water is pumped back into the boiler return. Since there is very little temperature difference between the boiler and the system almost no heat is transferred to the system in this small flow of water… nearly all of it goes back into the return of the boiler. As the boiler warms up, the temperature differential between the boiler and system will increase to a few degrees and a little bit more heat is transferred to the system, with most of the boiler heat continuing to go back into the boiler. As the boiler steadily comes up to temperature, the amount of heat transferred from the boiler loop to the system loop will slowly increase. A fixed “injection” flow rate between the boiler with a steadily increasing delta tee will gradually increase the amount of heat transfer to the system. As the boiler gets hotter, a larger and larger amount of heat is transferred. By setting the flow rates carefully with a fixed bypass, the boiler can get up to temperature in a reasonable amount of time, just like it does with a low mass fin tube baseboard system, essentially mirroring boiler operating temperatures of a cast iron boiler in a low mass system. With many high mass, converted gravity systems you have the additional advantage that for most of the heating season, the system is not at room temperature, but well above room temperature, so the return temperature from the system is much higher than a low mass fin tube system.
    However, this is only part of the picture. The other part is quite clearly demonstrated by the operational cycle of cast iron condensing design boilers. When the heating cycle ends, the pump needs to be shut off at the same time as the boiler flame. Upon shut off, the cast iron boiler heat soaks and drives up the average boiler temperature as the heat in the castings is transferred to the water but is no longer removed by water flow. This extra heat distributes through the boiler and increases the temperature of the lower portion of the castings that may have been operating in the condensing range and dries out the castings, so very little corrosion occurs. Anyone that has worked with the Weil McLain CG series boiler, a very low water content cast iron boiler, will likely be very familiar with this phenomenon…. When these boilers end a firing cycle and the pump shuts off at the same time after running at high temperatures, the water in the boiler will often begin to boil even under the higher pressures in a closed system. These boilers do particularly well in converted gravity systems often without any bypass piping and have little corrosion.

    A boiler bypass set up works similarly. A high delta tee is created across the boiler, but at very low flows, so the average boiler temperature can rise much more quickly than the system temperature. Upon end of the firing cycle and with the pump shutting down, the same heat soak process occurs to dry out the castings, if need be.
    I have found on my own converted gravity system using boiler bypass piping that having the pump shut down is critical to making sure that the heat soak/ drying cycle occurs. I spent one heating season with the pump running continuously to help improve heating during remodeling, and most of the pins at the bottom of the boiler completely corroded off. I learned my lesson and the pump is always cycled now.
    Also, of importance to this discussion is the combustion efficiency of the boiler. I am fortunate to have one of the early 1990’s transitional design atmospheric gas boilers that have much denser pinning on the heat exchanger and still have the older, much more efficiently burning cast iron burners. The combustion numbers for this boiler are at about 20 To 30% excess air (higher co2 numbers) along with increased heat transfer of a modern heat exchanger. All newer atmospheric boilers I’ve tested, except the Dunkirk 249 series, run about 50% excess air, which decreases the condensation temperature of the boiler. Most new atmospherics probably don’t have any condensation issues until return water is between 110 and 120F, especially since the temperature of the casting on the flame side is much higher than the water temperature side.
    I have another atmospheric cast iron boiler rated at 150,000 btu/hr input that heats about a 5000 sq ft 1950’s 1 inch steel pipe in concrete slab radiant floor. This boiler is piped with a system bypass with a P/S loop going out to the system. This system probably never sees return temperatures above 85F, even in the coldest weather and the boiler has no corrosion issues. The floors never even feel warm, just not cold.


    So how does most of the flow go back to the boiler when it is cold, but less and less as it heats?
    With a valve in a fixed position?

    A famous, industry trainer taught me, whatever goes into a tee, a fitting, must come out of a tee or fitting

    Sounds to me like shutting the pump off at the end of the cycle is protecting more then the fixed bypass.
    What is the gpm flow rate of the boiler pump? Somehow it moves the full capacity of what the boiler can accomplish to heat your home at some point in the cycle ?

    While I'm sure various means of bypass can work on different systems,to some degree, by design or more likely by shear luck since there is no published data on how, when and if to set the bypass at 30, 60, or 90%

    If you set your bypass at 90% get a high delta, warm the boiler, it cannot be supplying more then 10% to the system? Either now, or later. What goes into a tee, etc...
    Regardless if the boiler is cool or 180F hot. A zoned system would complicate this further, as flow demand changes.

    Hard to argue with the simplicity of coolant thermostats used in auto engines, TRV, Mix valves and protection devices. Wax or liquid based temperature sensing and response.
    It not about variable flow, but the variable delta tee. Btu's transfer by delta tee and flow rate together. If the delta tee is very low and the flow rate fixed, very little heat is transferred ( like on boiler start up). If the boiler stays at the same temperature as the system, no heat is transferred. As the boiler temperature gradually rises, but the flow rate stays fixed, the heat transfer increases as the delta tee increases. The boiler temperature has to rise in order for the btu's to be transferred to the lower temperature system water.



    The best way to come to understand how it works is to simple set one up and watch. That's how I finally figured it out and stopped using ESBE mixing valves ( which proved to be unreliable) on simple single zone converted gravity systems or slab radiant systems.
    To learn more about this professional, click here to visit their ad in Find A Contractor.
    Mad Dog_2
  • The Steam Whisperer
    The Steam Whisperer Member Posts: 1,090
    I just thought of another way to show the function of a boiler or system bypass in numbers:

    let's say a 90,000 btu/hr boiler and fixed flow of 3gpm from the boiler to the system.

    boiler supply is at 70F and system return at 70F = 0F Delta tee....no btus move to the system from the boiler loop

    boiler is at 80F and system return at 75F= 5F Delta tee.... 3 gpm @ 5F delta tee = 7000 btu to the system, 83,000 back into the boiler

    boiler at 90F supply and system return at 80F....3 gpm @ 10F delta tee =14,500 btu to the system, 75,500 btu back to the boiler

    boiler at 100F supply and system return at 85F... [email protected] 15F delta tee=22,000 btu to the system, 68,000 btu back to the boiler

    boiler at 110F supply and system return at 90F....3 [email protected] 20F delta tee= 30,000 btu to the system and 60,000 back to the boiler.

    boiler at 120F supply and system return at 95F....3 [email protected] 25F delta tee= 37,000 btu to the system and 53,000 back to the boiler

    this relationship continues with upwards temperatures and increasing delta tee until you hit a state of equilibrium at

    boiler at 190F supply and system return at 130F....3 [email protected] 60Fdelta tee= 90,000 btu to the system and 0 btu back to the boiler.

    these temperatures will vary depending on the system mass, boiler btu's and bypass flows, but they show the function of the bypass.


    To learn more about this professional, click here to visit their ad in Find A Contractor.
    gmcinnesMad Dog_2
  • gmcinnes
    gmcinnes Member Posts: 107
    Upon shut off, the cast iron boiler heat soaks and drives up the average boiler temperature as the heat in the castings is transferred to the water but is no longer removed by water flow. This extra heat distributes through the boiler and increases the temperature of the lower portion of the castings that may have been operating in the condensing range and dries out the castings, so very little corrosion occurs.


    That sounds very plausible @The Steam Whisperer when it warms up a bit, and the boiler doesn't need to be running so much I'm going to investigate that (just out of curiosity - i'm really pleased with how it's performing).

    The pipe size of my boiler bypass is smaller than specified in the manual, but if it's still doing it's job I'm ok with it.

    That's a nice intuitive picture of how the bypass functions.

    Mad Dog_2
  • hot_rod
    hot_rod Member Posts: 18,279

    I just thought of another way to show the function of a boiler or system bypass in numbers:

    let's say a 90,000 btu/hr boiler and fixed flow of 3gpm from the boiler to the system.

    boiler supply is at 70F and system return at 70F = 0F Delta tee....no btus move to the system from the boiler loop

    boiler is at 80F and system return at 75F= 5F Delta tee.... 3 gpm @ 5F delta tee = 7000 btu to the system, 83,000 back into the boiler

    boiler at 90F supply and system return at 80F....3 gpm @ 10F delta tee =14,500 btu to the system, 75,500 btu back to the boiler

    boiler at 100F supply and system return at 85F... [email protected] 15F delta tee=22,000 btu to the system, 68,000 btu back to the boiler

    boiler at 110F supply and system return at 90F....3 [email protected] 20F delta tee= 30,000 btu to the system and 60,000 back to the boiler.

    boiler at 120F supply and system return at 95F....3 [email protected] 25F delta tee= 37,000 btu to the system and 53,000 back to the boiler

    this relationship continues with upwards temperatures and increasing delta tee until you hit a state of equilibrium at

    boiler at 190F supply and system return at 130F....3 [email protected] 60Fdelta tee= 90,000 btu to the system and 0 btu back to the boiler.

    these temperatures will vary depending on the system mass, boiler btu's and bypass flows, but they show the function of the bypass.


    Could it be your boiler output is larger then the design day load? If so you could be warming the boiler as you deliver some heat.
    If the actual load is 30K and boiler output is fixed 90K then you could bypass the % difference and warm the return faster.

    This diagram has some actual, realistic flow and temperature numbers to show how bypass, pumping, piping, even P/S piping cannot provide absolute return protection.

    Without knowing and being able to respond to that return temperature, it will be a hit and miss exercise.
    Your system needs to be out of transient condition to know and adjust the blend, and get accurate data.

    The measured delta is an indication of how much heat is being delivered. The heat emitters, not the boiler are in control of that. Assuming the pump(s) and boiler are fixed speed🤓
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Mad Dog_2gmcinnes
  • Mad Dog_2
    Mad Dog_2 Member Posts: 3,942
    edited February 4
    Great conversation.  Yes, The Viessman Manuals were like a  treat to look at. - so educational.  The Peerless Colors of Heat Series was awesome.  I still have on my Barn Loft Office book shelves.  My hydronic brother, The brilliant Mark Hunt resides at Peerless for many years now.  A great American company too.  Never had ANY real problems with a Peerless boiler and occasional ones were taken care or fast.  Thanks Pete Morgan!  Two Long Island Heating legends I've always admired are Jimmy The Gent Burke (of Levittown-East Meadow-Johnson City (Elmira)-back to East meadow-Medford (Deep Suffolk)-Finally West Palm 🌴 Beach Florida/Medford)
    Cut his teeth in the oil business doing the boiler-a-day circuit.  Peerless Boilers ruled the day.  Ron Jr. Who came right behind Jimmy followed the same tough road.  Jimmy and I put many Peerless Boilers in 
    Together.  At Triple 👑 Crown, my own installation company, I became largely a Burnham man. Why?  I  loved the blue color and it was NOT W/M (VERY COMMON ON LONG ISLAND) another great company.   I wanted to distinguish my company from the Wolf  pack.  Turned out to be a very good Company to follow to this day.  I miss Glenn Stanton so much.  He " learned me' so  much, looked after me as a young contractor, put me in the Burnham Calendar 📅 3 yrs in a row and once had the reststocking fee "disappeared' when an unscrupulous customer canceled a job
    (Replacement of all the Large, CI Steam Radiators in a huge  3 story Dutch Colonial , With brand new, Gorgeous  Burnham Classic Victorian scrolled/filigreed CI steam  Radiators ) there was about twenty monsters.  At $125 per section. Back then,  the restocking fee was like 10 Large (Thousand)!!!!   I was freaking out! I did tons of work for the wife who was a great lady.. always dealt with her but was paid with his NYC Construction company checks....No Problem!   I felt like he thought that he/they gave me a lot of work and $$$ and that now,, I !!! Was gonna DO SOMETHING FOR HIM!!! So we have like 5 very heavy  pallets sitting in Christ Plumbing Supply New Hyde Park Long Island (est. 1810) full of almost two dozen  brand, spanky-new Burnham Classic Victorian rads.  This one Saturday, He's home and for the first time after dealing with her on 80K worth of work, I'm dealing with him.  He walking around with Coffee (didn't offer me any) and I see the wife is nervous.  He's a pretty Tough-acting atleast  Aggressive North Queens guy (Well to do area) and he starts walking me around the house "reviewing" the job that  😀 I was about to start on Monday.  As soon as I git my long overdue deposit check.. His wife was smart and so nice and had approved everything with me on a handshake 🤝 like all our past dealings.  Having never gotten a DEPOSIT for these
    Butes, my stomach is starting to turn. Suddenly, everything is IF and WHEN I DECIDE to blah blah "give" this job to you!   I cheerfully explained that the rads were ready to be delivered Monday and start swapping them out.  'yeah, no problem, I just need you to sign this!!" He pulls a written up detailed contract on MY letterhead (they must have taken one of mine and redid it on a computer 🖥 .
    I read it quickly but basically he wanted me to LIE and claim that I did a complete fire 🔥 Sprinlker reroute Job to make room for his Electrical Conduit The bill he wanted me to perpetrate fraud which  was for like $60 Large (thousand) in a NYC commercial building where I wasnt even licensed to do sprink work!! Fire Sprinkler work is LIFE VERSUS DEATH STUFF....NO WAY MAN...I guess because I'm fairly well spoken  (Thanks Mom and Stony Brook) and I lived in Long-GUYLAND" (Brooklyn Queens pronounciation of The Isle of Long), he could strong arm me..  What he failed to realize is a grew up Irish with Jimmy The Gent Burke (Lufthansa heist..Played brilliantly by Bobby Deniro in Goodfellas) as a neighbor  in the very rough South Ozone Park and the very tough but wealthier  Howard Beach (Organized Crime suburbs of the World.  In the late 1980s, we had 4 out of 5 Families' Bosses living in Howard Beach!) Neighborhoods, so you were NOT going to strong  arm me!! When dealing with a certain "element" think Goodfellas ha ha, I have to bring out my inner "How'beach" Posture. (Think Deniro playing Jimmy The Gent Burke in Goodfellas).  I told him in no uncertain terms, How'beach style, that I was NOT dirty and corrupt like him AND that if he wanted to cancel the job, he had a 10k bill for "restocking" fee to give me!    He said :" ain't happenin Cuz!!! Unless you sign....."  Getting very upset and trying to calm the situation, the very nice wife began to cry 😢 thinking it was about to escalate.
    There was an awkward silence for about 30 seconds..seeing who would relent.  Dreading the 10k restocking fee that I was now responsible for, I was NOT feeling 😪 too well.  There's a good reason why I had avoided going in to "that life" which a good 40% of my classmates - in Catholic School no less! - went to that other side.  My parents grew up around them too, had close friends, not so close friends - we Played, fought, Broke bread together side by side but WE...became Horse 🐎 Racing Trainers, Racing Judges, Funeral Directors,  Private eyes, NYPD and FBI, US Military,  lawyers, plumbers (me) sanitation guys (good city job), Car mechanics; Pilots, Sheriff Deputies, pharmaceutical salesmen....actual occupations of my family and freinds who didn't go in to "the life.' I was raised better than this and as tempting as it was....' I was next to speak: "No can do, bro...I'm obviously not corrupt like you....!"  He opened with with a barrage of nasty curse words like only a Brooklyn-Queens guy can deliver.  One last look in the eye, I did a military about face and left...Now what do I do?  I was DEAD...I had to pay 10 large or EAT all the radiators....If I remember correctly, I sought solace on The Wall and my great Life and Business mentor, Dan.  "Call Glenn Stanton...if anyone can help you, it will be him!  Dan gave me Glenn's Personal cell (In what other industry does a regular Joe The Plumber like me, have access to Giants....and Rock Stars ????  This is Dan Holohan's World!)  Glenn picked up, recalled meeting me at A Burnham event recently and followed the Exploits of Mad Dog 🐕 On The Wall.  Glenn listened and said "No worries, Matt,I'll make a call Monday.  Call so and so at the distributor after lunch and he'll take them back..."NO 10 K  RESTOCKING FEE!!!!"  Damn!  I felt like I just WON 10K!!  So Monday, I call the guy who was fighting with me on Saturday about the restocking fee, and he says..."Why didn't you TELL me who you knew??  With a phony 😃 smile.  Well pick up the 5 skids from Christ Tommorow...you're good to go, bro!!"   Lesson: Do the right thing, ALWAYS, 
    Surround yourself with high quality people like The Holohans and the HH community and ALWAYS GET A HEFTY DEPOSIT for leverage.   Mad 🐕 Dog. 
  • Mad Dog_2
    Mad Dog_2 Member Posts: 3,942
    edited February 4
    Sorry I trailed off...memories...I HATE most directons and usually look at them quickly, look at picture of the finished products, sort thru the parts then wing it.  I agree about 
    Writing ✍ instructions that ANYONE can follow. I do the same in my writing.  So does Dan.  When inquisitive people want ti know 
    "SO who IS this Dan Holohan and why is he so revered in YOUR industry??????"
    I explain simply: "as a 20 yr old working with his father at Wallace Eannace Wholesale,  he took down old, dusty Engineering books on steam and hot water read them and put them in PLAIN ENGLISH and made the topics funny...so that DUMMYS like me can understand! "
    I always get a laugh out of them and the light bulb 💡 goes off in their heads. Mad Dog
    Larry WeingartenErin Holohan Haskell
  • Hoagie
    Hoagie Member Posts: 4
    Hot Rod, the Rule of Thumb we suggest for the boiler bypass (as shown in the Color Water Drawing) is to watch the thermometer on the return pipe, which is installed downstream of the bypass. Then time how long it takes the temperature to get from cold start to 125º. The ball valve should be opened only enough to get to 125 within 2-3 minutes.

    Essentially every cold-start boiler will go through a flue gas condensing period. For a CI boiler with copper baseboard, it’s normally about 2-3 minutes anyway. The boiler bypass will reduce the time that tens of gallons of relatively cold system water from an older high volume system flows through the boiler.

    Granted, a certain amount of bypassing water will reduce the delivery of boiler water to the system during steady state operation, but without any low temperature protection the boiler will rot out in a fairly short time, typically a couple of years, from what I’ve seen.

    Peerless had a gas-fired CI boiler with a thermostatic bypass valve for about 20 years. It worked fairly effectively, but the bypass element typically failed by about 10 years. The bypass element on the boiler eventually went out of production, which left a repiping job as the typical alternative.

    The Hydrostat model 3250+ is shipped on Peerless oil-fired boilers, and the model 3200+ is shipped on Peerless gas-fired boilers. The circulator hold-off feature is turned on by default on both models. I haven’t heard of any excessive corrosion problems since its introduction, although old converted gravity systems are not the most common anyway.
    gmcinnes
  • psb75
    psb75 Member Posts: 639
    Dan H. knows how to write a good paragraph, or two. And he's also spare and succinct with his use of detail. Very easy and enjoyable to read--I think you'll agree.
    gmcinnesErin Holohan Haskell
  • hot_rod
    hot_rod Member Posts: 18,279
    edited February 4
    Hoagie said:

    Hot Rod, the Rule of Thumb we suggest for the boiler bypass (as shown in the Color Water Drawing) is to watch the thermometer on the return pipe, which is installed downstream of the bypass. Then time how long it takes the temperature to get from cold start to 125º. The ball valve should be opened only enough to get to 125 within 2-3 minutes.

    Essentially every cold-start boiler will go through a flue gas condensing period. For a CI boiler with copper baseboard, it’s normally about 2-3 minutes anyway. The boiler bypass will reduce the time that tens of gallons of relatively cold system water from an older high volume system flows through the boiler.

    Granted, a certain amount of bypassing water will reduce the delivery of boiler water to the system during steady state operation, but without any low temperature protection the boiler will rot out in a fairly short time, typically a couple of years, from what I’ve seen.

    Peerless had a gas-fired CI boiler with a thermostatic bypass valve for about 20 years. It worked fairly effectively, but the bypass element typically failed by about 10 years. The bypass element on the boiler eventually went out of production, which left a repiping job as the typical alternative.

    The Hydrostat model 3250+ is shipped on Peerless oil-fired boilers, and the model 3200+ is shipped on Peerless gas-fired boilers. The circulator hold-off feature is turned on by default on both models. I haven’t heard of any excessive corrosion problems since its introduction, although old converted gravity systems are not the most common anyway.

    I have no problem with manuals showing options, explaining good, better, best. US Boiler came real close to that in the X series manual.
    The point I’m trying to make is their last option with variable speed, does not, will not, can not provide 100% protection.
    I merely suggest that show absolute protection with a thermostatic valve, or properly applied VS circ. Is that too much to ask?

    And if not, we can continue to deal with failed boilers and the arm wrestling to provide or deny warranty and get a bad rap for the product and the unknowing installer. In this case reading the installation manual doesn’t provide the best options.

    High mass radiant are still being installed with conventional boilers, that is where vert high mass will present problems quickest.

    As far as those that chose to not read the manuals, dumbing down the industry benefits who?

    I’m an old, although not a mad, dog 🧐. I enjoy and learn by reading online here, or on paper. None of us will ever know it all. Teach your parents well…
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • The Steam Whisperer
    The Steam Whisperer Member Posts: 1,090
    edited February 4
    hot_rod said:

    I just thought of another way to show the function of a boiler or system bypass in numbers:

    let's say a 90,000 btu/hr boiler and fixed flow of 3gpm from the boiler to the system.

    boiler supply is at 70F and system return at 70F = 0F Delta tee....no btus move to the system from the boiler loop

    boiler is at 80F and system return at 75F= 5F Delta tee.... 3 gpm @ 5F delta tee = 7000 btu to the system, 83,000 back into the boiler

    boiler at 90F supply and system return at 80F....3 gpm @ 10F delta tee =14,500 btu to the system, 75,500 btu back to the boiler

    boiler at 100F supply and system return at 85F... [email protected] 15F delta tee=22,000 btu to the system, 68,000 btu back to the boiler

    boiler at 110F supply and system return at 90F....3 [email protected] 20F delta tee= 30,000 btu to the system and 60,000 back to the boiler.

    boiler at 120F supply and system return at 95F....3 [email protected] 25F delta tee= 37,000 btu to the system and 53,000 back to the boiler

    this relationship continues with upwards temperatures and increasing delta tee until you hit a state of equilibrium at

    boiler at 190F supply and system return at 130F....3 [email protected] 60Fdelta tee= 90,000 btu to the system and 0 btu back to the boiler.

    these temperatures will vary depending on the system mass, boiler btu's and bypass flows, but they show the function of the bypass.


    Could it be your boiler output is larger then the design day load? If so you could be warming the boiler as you deliver some heat.
    If the actual load is 30K and boiler output is fixed 90K then you could bypass the % difference and warm the return faster.

    This diagram has some actual, realistic flow and temperature numbers to show how bypass, pumping, piping, even P/S piping cannot provide absolute return protection.

    Without knowing and being able to respond to that return temperature, it will be a hit and miss exercise.
    Your system needs to be out of transient condition to know and adjust the blend, and get accurate data.

    The measured delta is an indication of how much heat is being delivered. The heat emitters, not the boiler are in control of that. Assuming the pump(s) and boiler are fixed speed🤓
    This is with a boiler sized to the design heat loss.... as you can see on the last iteration of the rising temperatures, once it reaches a certain delta tee all of the btu's will be delivered to the system on design day.

    I watch my boiler go through this pattern all the time and the hot water boilers that we have with a bypass ( needed virtually universally in old cities like Chicago).

    The best I can tell you is to set one up and watch it work. And yes you are right that it's not a 100% solution.... in extreme warm days with short boiler cycles, it may not raise the temperature to above condensing, but the boiler will still dry out at the end of the cycle when the warm boiler surfaces dry out.
    Decades of its proper application and use show how well it works for cast iron atmospherics.
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • Paul Pollets
    Paul Pollets Member Posts: 3,573
    It seems to me that it wouldn't be hard for manufacturer's to show preferred methods for common applications and methods for boiler protection that work. Viessmann does it. Ultimately putting the schematics online or on CD would be helpful.
  • hot_rod
    hot_rod Member Posts: 18,279

    It seems to me that it wouldn't be hard for manufacturer's to show preferred methods for common applications and methods for boiler protection that work. Viessmann does it. Ultimately putting the schematics online or on CD would be helpful.

    We all agree the potential for extended cold operation exists. And we know the workable fix. Two sentences and a few drawing, drawings which already exist could eliminate any questions.

    If the boiler corrodes away and the piping was wrong, that is an easier refusal for the boiler manufacturer.
    You notice the stronger wording about connecting to non barrier tube showing up in cast boiler manuals.
    Same concept really.

    Seems to be one brand that comes up constantly for failed castings, maybe it is installation or operator error. What an opportunity to lead the industry with the correct information.

    If falls on the trainers in our industry to get the correct information out to the field.
    Consultants, service mangers, tech support people need to get it right also, if that is what your claim to fame is😚
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Paul Polletsmattyc
  • hot_rod
    hot_rod Member Posts: 18,279

    hot_rod said:

    I just thought of another way to show the function of a boiler or system bypass in numbers:

    let's say a 90,000 btu/hr boiler and fixed flow of 3gpm from the boiler to the system.

    boiler supply is at 70F and system return at 70F = 0F Delta tee....no btus move to the system from the boiler loop

    boiler is at 80F and system return at 75F= 5F Delta tee.... 3 gpm @ 5F delta tee = 7000 btu to the system, 83,000 back into the boiler

    boiler at 90F supply and system return at 80F....3 gpm @ 10F delta tee =14,500 btu to the system, 75,500 btu back to the boiler

    boiler at 100F supply and system return at 85F... [email protected] 15F delta tee=22,000 btu to the system, 68,000 btu back to the boiler

    boiler at 110F supply and system return at 90F....3 [email protected] 20F delta tee= 30,000 btu to the system and 60,000 back to the boiler.

    boiler at 120F supply and system return at 95F....3 [email protected] 25F delta tee= 37,000 btu to the system and 53,000 back to the boiler

    this relationship continues with upwards temperatures and increasing delta tee until you hit a state of equilibrium at

    boiler at 190F supply and system return at 130F....3 [email protected] 60Fdelta tee= 90,000 btu to the system and 0 btu back to the boiler.

    these temperatures will vary depending on the system mass, boiler btu's and bypass flows, but they show the function of the bypass.


    Could it be your boiler output is larger then the design day load? If so you could be warming the boiler as you deliver some heat.
    If the actual load is 30K and boiler output is fixed 90K then you could bypass the % difference and warm the return faster.

    This diagram has some actual, realistic flow and temperature numbers to show how bypass, pumping, piping, even P/S piping cannot provide absolute return protection.

    Without knowing and being able to respond to that return temperature, it will be a hit and miss exercise.
    Your system needs to be out of transient condition to know and adjust the blend, and get accurate data.

    The measured delta is an indication of how much heat is being delivered. The heat emitters, not the boiler are in control of that. Assuming the pump(s) and boiler are fixed speed🤓
    This is with a boiler sized to the design heat loss.... as you can see on the last iteration of the rising temperatures, once it reaches a certain delta tee all of the btu's will be delivered to the system on design day.

    I watch my boiler go through this pattern all the time and the hot water boilers that we have with a bypass ( needed virtually universally in old cities like Chicago).

    The best I can tell you is to set one up and watch it work. And yes you are right that it's not a 100% solution.... in extreme warm days with short boiler cycles, it may not raise the temperature to above condensing, but the boiler will still dry out at the end of the cycle when the warm boiler surfaces dry out.
    Decades of its proper application and use show how well it works for cast iron atmospherics.
    One other thermodynamic at work, in your system, Thermal Equalibrium . We covered it in a few different Idronics. Again now in Idronics 32, Troubleshooting Hydronics. Often misunderstood or ignored in design and troubleshooting.

    The inlet temperature to the boiler is established when the boiler output and load dissipation become equal.

    In a high mass system the outlet may never climb above 130 before the load satisfies so it becomes impossible for the bypass to raise the inlet temperature to or above 130. Remembering that you cannot stop the return temperature, let’s say 125 from blending with the 130 SWT. So it becomes physically impossible to magically blend that inlet up to a safe temperature

    I supposed if you sensored multiple locations on your piping, data logged it for a day at design, the numbers you see, are very close to what temperature you could calculate for the systems equilibrium. As shown a few posts ago with the Primary/ Secondary attempt at return temperature blending/ protection.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • hot_rod
    hot_rod Member Posts: 18,279
    Would 50 gpm bypass keep a boiler from low return? Maybe wire that delta T circ to 240V.
    The control aquastat is set at 180F. Certainly the boiler will go there? Not necessarily! Except when both circs are off and TT is jumpered😳


    The dynamics would be the same with high mass, large volume cast radiators, plug in your exact emitters, see where the numbers fall.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream