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Boiler Return Temperature - Too Low?

DJDrewDJDrew Member Posts: 45
Hello,

First, I have been reading these discussions for a few years now and have found the information very valuable!

I have a question about boiler return temperature for a new boiler we had installed last fall, and after parsing the data gathered over the winter wanted to make sure nothing needed tweaked.

Some background: Last fall we had a new gas boiler installed for our radiators in a 1938 2200sqf brick home. We replaced a 140btu boiler with a Slant/Fin Sentinel 105. I had received quotes from 5 different companies at the time and the one we picked was the only one who did a semblance of a heat-loss calculation. (Others wanted to either replace same or even higher since we have a lot of cast iron rads!) Upon further research with the Slant/Fin Heat Loss app, I gather that I'm either sized exactly right or could have even gone with either the Slant Fin Sentry 90 or even the Sentinel 70 if we were to insulate our roof and really button up the house.

Observation #1: Slant/Fin Sentinel 105 worked great all winter, we were never cold. Our thermostat is tied into a home automation server and when I reviewed the logs, I noticed that the Slant/Fin averaged about 45-55 minutes per call for heat. (i.e. Thermostat set at 70, at 68 the call for heat triggers and the boiler would run for 45-55 minutes to bring the temp back to 70.) The old boiler would run for 25-35 minutes on average under similar scenarios. These are the averages for the season (milder days would be less and colder days would be longer.)

Observation #2: The Slant/Fin, after running for 45 minutes would still only show a water temperature of 135 degrees on the HydroStat. (I never monitored the old boiler's temperature, so I can't compare.) On super cold days, the temp might get to 140 after the boiler ran for 90 minutes.

Question: Assuming the behavior in the first observation is correct, I am guessing the reason for the low temperature is because this old house is overloaded with cast iron radiators. That said, If the boiler is only getting to the mid 130's on average, should I be concerned with the cast iron boiler rotting since much of the time it is in the 115-130 range as it heats up? I have read several places that to prolong the boiler life I should be seeing temps in the 140 range.

The boiler has 1 1/4" in/out and the installer put a 1/2" bypass loop in during the install to help keep return temperatures up. I am guessing the bypass loop is not cutting it. Should I look at having the bypass loop converted to include a Danfoss Thermostatic Boiler Protection Valve to ensure a higher boiler operating temperature?

Sorry for the lengthy post, but I wanted to give a complete picture of the situation. Any thoughts or advice would be most helpful!

Cheers,
Drew



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Comments

  • SuperJSuperJ Member Posts: 557
    Sound like you need some sort of boiler protection strategy.
    There are different valve and pump arrangements to accomplish that. Could you post a diagram or some pictures of your system?

    I'm assuming the pump is between the boiler and the bypass you mentioned. What is the pumping arrangement for your system? If it is primary secondary, then you might consider some other methods for boiler protection.

    You could install a valve like you mentioned (I'm not familiar with that exact one). 1/2" bypass is probably too small. Probably install it something like this:


    Here is another option, that could give you some more flexibility.
    http://apps.taco-hvac.com/products/hydronic_accessories/pressure_valves/i_series_mixing_valves/index.html

    One more point: Since your boiler seems to be sized nicely you could reduce the deadband on your thermostat from 2deg down to 1f or less and still not short cycle the boiler. You'll have more even temperatures too.
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 6,109
    Yes. If your reading are accurate I would install a three way valve or a pump. There are may ways to solve the problem. I prefer a three way valve with an electronic controller sensing return temperature to keep the return water above 135.
  • ZmanZman Member Posts: 5,334
    edited July 2018
    @DJDrew
    I would recommend an anti condensing strategy of some sort to protect the boiler and the flue, especially if the flue is located in an unheated space.
    Slant fin does not seem overly concerned about it. There are no piping diagrams showing anticondensate loops in the O&I. This is their solution to the problem. I don't see any harm in trying this setting. I would keep an eye on the circulator to make sure it is not cycling constantly.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • newagedawnnewagedawn Member Posts: 549
    the boiler sounds undersized, the temp of water should be able to reach 180 no problem, not that you need to run it that hot with rads, a bigger bypass would help maintain a higher temp of return, but you would need a 1 inch, as the 1 inch would carry the load needed to do that, please post a pic or 2 of the complete boiler piping, so we can see whats happening
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"
  • HVACNUTHVACNUT Member Posts: 2,629
    The boiler is 1 1/4 in and out, but what size is the heat loop?
    What model Hydrostat? The ones I've used on oil boilers have "boiler reset", or thermal targeting. Temperatures according to the heat demand. It can be adjusted for high limit, minimum temp, and level of economy. Check the paperwork (that should have been left by the installers) to see if your model has these options. If so, try setting the minimum temp to 140° and drop the economy setting 1 setpoint at a time, over a period of days until return water temps reach at least 135°.

    Did anyone quote a modcon?
  • SuperJSuperJ Member Posts: 557
    Here is snipping from the manual, it covers a thermostatic bypass control. (and note the anticipator settings, sounds like you could adjust yours because of the long cycles).


  • ZmanZman Member Posts: 5,334

    the boiler sounds undersized, the temp of water should be able to reach 180 no problem, not that you need to run it that hot with rads, a bigger bypass would help maintain a higher temp of return, but you would need a 1 inch, as the 1 inch would carry the load needed to do that, please post a pic or 2 of the complete boiler piping, so we can see whats happening

    @newagedawn
    Just because it can't heat massive radiators to 180 does not mean it is undersized. I think it is likely oversized substantially. It has no problem heating the house.
    The installer should have foreseen this and installed an effective bypass loop. The manufacture should assure their product has a long and happy life by including a bypass piping detail in the I&O.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • DJDrewDJDrew Member Posts: 45
    Thanks everyone for the feedback so far! This has been very helpful! @SuperJ I like the thought on adjusting the call temp of the thermostat.

    @Zman Good thought on the circulator hold option! That is the Hydrostat we have and we did enable that option toward the end of the heating season in the Spring. With the circulator hold option enabled, we noticed it would run for 30-45 seconds and then off for about 90 seconds... which seems like a short duty cycle for the circulator? However, with the circulator only running at higher temperatures, the overall boiler cycle time dropped by about 4-5 minutes on the call for heat.

    Attached are some images of the install; to help get your bearings, the circulator is on the return side and the expansion tank is on the hot output side of the boiler. The system is a single zone. And the 3rd image shows the bypass loop more closely, which after inspection might actually be 3/4".





  • hot_rodhot_rod Member Posts: 12,025
    https://www.caleffi.com/usa/en-us/technical-magazine

    Read about thermal equilibrium in this u
    Issue. The heat emitters are in charge of the boiler operating condition
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • SuperJSuperJ Member Posts: 557
    hot rod said:

    https://www.caleffi.com/usa/en-us/technical-magazine

    Read about thermal equilibrium in this u
    Issue. The heat emitters are in charge of the boiler operating condition

    Direct Link: https://www.caleffi.com/sites/default/files/file/idronics_23_na.pdf
  • ZmanZman Member Posts: 5,334
    I don't like those circulatory cycle lengths either. You might experiment with throttling the zone isolation valves a bit. Adding resistance to the zones will force more water through the bypass.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • SuperJSuperJ Member Posts: 557
    Here is my Cadillac solution:

    If you just use a thermostatic valve on the boiler return with a single pump system, the flow to the house will be starved while the boiler heats up. This means rads closer to the boiler or on circuits with less pressure drop are going to get flow first, while the far corners could be starved for flow resulting in uneven heating.

    With a pump dedicated to the loads, a 3 way valve (OA Reset and Boiler Protect functions), and a boiler dedicated boiler pump: All the rads will get flow right away, and the SWT will warm up gradually as the boiler RWT comes up to temp resulting in smooth even comfort, and worry free boiler operation.
  • HVACNUTHVACNUT Member Posts: 2,629
    Except for the circulator being in the wrong location, it's a nice job.
    Their should be no reason not to get 140° return temp after a long run time.
    Does the boiler ever make limit during the long run times, or does the thermostat satisfy?
    What is the limit setting?
    Is that 007 the correct size pump for the application? It might need a different circ to match the load. Package boilers need to fit in the shipping crate, not give the correct circulator.
    Pros, Cons? A make on tempature rise (140°) aquastat at the halfway point of the loop. Looking affordability wise and still have funtion.
  • ZmanZman Member Posts: 5,334
    @HVACNUT
    If you have huge high mass emitters, you may never get 140 return temps and there is nothing wrong with that. A snowmelt system is a good example of this.
    The important thing is to protect the boiler from condensation.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • hot_rodhot_rod Member Posts: 12,025
    I too would look at a 3 way thermostatic boiler protection valve.
    That boiler will not live a long happy life at those operating conditions

    Protect what you have ASAP.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • DJDrewDJDrew Member Posts: 45
    edited July 2018
    SuperJ said:

    Here is my Cadillac solution:

    If you just use a thermostatic valve on the boiler return with a single pump system, the flow to the house will be starved while the boiler heats up. This means rads closer to the boiler or on circuits with less pressure drop are going to get flow first, while the far corners could be starved for flow resulting in uneven heating.

    With a pump dedicated to the loads, a 3 way valve (OA Reset and Boiler Protect functions), and a boiler dedicated boiler pump: All the rads will get flow right away, and the SWT will warm up gradually as the boiler RWT comes up to temp resulting in smooth even comfort, and worry free boiler operation.

    @SuperJ Interesting observation! I had not thought that the thermostatic valve would change the pressure balance of the system for the rest of the house.

    I did imagine the first case where the boiler will be heating itself for the first few minutes and then slowly trickling heat out to the rest of the house. However, I didn't think the heat trickle would impact the pressure balance. I thought it would just behave similarly to how the circulator is cycling on and off, limiting the heat output until the boiler is satisfied.
  • DJDrewDJDrew Member Posts: 45
    HVACNUT said:

    Except for the circulator being in the wrong location, it's a nice job.

    @HVACNUT Where would the correct location for the circulator be? If I have to partially drain the system, (I can close the main supply and return valves feeding the trunk lines to the radiators) is it worth correcting when I address the bypass loop issue?
  • DJDrewDJDrew Member Posts: 45
    Zman said:

    I don't like those circulatory cycle lengths either. You might experiment with throttling the zone isolation valves a bit. Adding resistance to the zones will force more water through the bypass.

    @Zman Currently the main feed/return trunks T above the boiler, with ball valves on each side of the T. Since I do have those main valves on the supply and return trunk lines, this would be an easy experiment. I currently only use the valves to balance the resistance between all the radiators on the back of the house with those on the front of the house so everything heats up at the same time.
  • hot_rodhot_rod Member Posts: 12,025
    The bull headed tee on the supply above the boiler needs to be corrected, getting an accurate balance will be tough.

    With a high mass heat emitter another option would be constant circulation with TRVs. You have a large “flywheel” to try and control with an on/ off control logic.

    It is very similar to radiant slabs, slow to respond and often overshoots.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • HVACNUTHVACNUT Member Posts: 2,629
    edited July 2018
    > @DJDrew said:
    > Except for the circulator being in the wrong location, it's a nice job.
    >
    >
    >
    > @HVACNUT Where would the correct location for the circulator be? If I have to partially drain the system, (I can close the main supply and return valves feeding the trunk lines to the radiators) is it worth correcting when I address the bypass loop issue?

    The circ should be on the supply, pumping away, down stream from the air scoop. It'll work the way it is but pumping away is correct.
    Can your Hydrostat maintain a minimum boiler temperature and drop power to the circulator when the temperature meets that setpoint? With that option and the bypass, boiler temp should be able to maintain 140°
    And a ball valve isn't the best for manual tempering. Should've been a Globe valve.
  • DJDrewDJDrew Member Posts: 45
    edited July 2018
    HVACNUT said:


    The circ should be on the supply, pumping away, down stream from the air scoop. It'll work the way it is but pumping away is correct.

    Can your Hydrostat maintain a minimum boiler temperature and drop power to the circulator when the temperature meets that setpoint? With that option and the bypass, boiler temp should be able to maintain 140°

    And a ball valve isn't the best for manual tempering. Should've been a Globe valve.

    Interesting. Seems like changing the circulator position as you describe would be a major re-plumbing job to fix, although I do recall hearing that as a best practice. While we do have 2 stories + and attic, so 3 stories I guess, it seems like page 17 of the install manual recommends both layouts.
    [Perhaps if I find someone in need of a boiler that is the size of the SE-105, I'll sell it to them and upgrade ours to a smaller, more efficient, one and fix the circulator so it is pumping away in the process.]

    The Hydrostat doesn't seem to have the function you are describing. There is a minimum temperature, but then the boiler would run then all the time. According to the manual, "the low limit is designed to maintain temperature in boilers equipped with tankless coils used for domestic hot water."
  • HVACNUTHVACNUT Member Posts: 2,629
    > @DJDrew said:
    > The Hydrostat doesn't seem to have the function you are describing. There is a minimum temperature, but then the boiler would run then all the time. According to the manual, "the low limit is designed to maintain temperature in boilers equipped with tankless coils used for domestic hot water."

    Correct. Its mostly used for boilers with a tankless, but setting the low to 140° will help prevent condensing by turning off the circulator. The burners will continue, and the circ will turn on when it meets the differential, which can be adjusted by you. With the bypass, the circ shouldn't short cycle. You'll probably have to play with the differential and the flow at the bypass. And again, it looks like an 1 1/4 or 1 1/2 main loop, and with large emitters, I dont think the 007 is right for the application.
  • hot_rodhot_rod Member Posts: 12,025
    If you do have an opportunity to replace the boiler a mod con would be an ideal replacement, if in fact you can heat the home with 140° SWT.

    The low return temperatures would keep the boiler efficiency up, and no return protection device would be needed.

    With a carefully adjusted outdoor reset you could end up with near constant circulation, a good way to run high mass radiators for perfect comfort, modulate temperature based on load of the space.

    As HVAC mentioned the circulator should be sized to move the required gpm for the load, probably at a low head in a large pipe system like that.

    Any problems keeping the upper radiators purged and air free? Pumping away from the expansion tank is a good way to solve air elimination issues.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • DJDrewDJDrew Member Posts: 45
    @hot rod We looked into a mod con boiler. One of the issues is that this area of the house is completely underground and the chimney is ~48' to the top. All the companies and even one rep came and no one thought piping that high up the chimney would be good long-term. Another option would be to snake the exhaust lines around the basement to an exterior wall, however all the ideal spots would either exhaust onto a patio or be within 2' of a window. One contractor wanted to trench up to the exterior wall and run the exhaust underground and up away from the house behind a bush, which seemed a little too wonky for us.

    Exhaust issues aside, every mod con estimate came in at over 40% the cost of the traditional cast iron boiler. Our fuel bills this winter averaged in the 150-170 range, so the payback for the added fuel savings would have taken awhile with the upfront cost of the mod con.

    I really did want to go high efficiency, the cost (and the troublesome exhausting issue) were the drawbacks.
  • DJDrewDJDrew Member Posts: 45
    @hot rod and @HVACNUT Is there a circulator that you'd recommend?

    In general, we have not had much issue keeping the radiators bled, so I am not sure it is worth the cost to relocate the circulator, but I am open to replacing it with one more matched to the load.
  • hot_rodhot_rod Member Posts: 12,025
    Too bad about all the issues with a mod con upgrade, I can see how you made the decision. What you have can and will work fine, a few upgrades would help protect it.

    While pumping away is ideal and always recommended, plenty of boilers are piped like yours and operate fine for decades.

    If you plan on adding a return protection valve, or other piping changes then I would do both at the same time while the system is drained. The pump could stay where it is, jut move the expansion tank connection down to the inlet of the cir, is another option.

    The best way to size and select a circulator pump is to analyze and calculate the circuit. I will add a link to a journal that takes you through that process.

    If you had some gauges you could see where the current circulator is operating, the idronics journal I added will take you through those steps also. Many of the new small circulators like that are multi speed, so you can do some flow adjusting and balancing by changing the speed.

    Really my biggest concern would be how long the boiler operates with the return temperature below 130- 140°. You could buy a few inexpensive digital thermometers and take some measurements. Azel makes a nice dual temperature, battery operated temperature gauge.

    Strap one probe on the supply out of the boiler, one on the return piping. That will show you give you the operating delta. Probably see a wide ∆ at start up, closing down as the system reached stepping. Watch the temperature on the return temperature gauge as the boiler runs through a period of time, 15- 20 minutes for example.

    We typically want the boiler to get above 130° at the return within 10 minutes of every light off. Also the boiler should run at that condition, above dew point, for at least 10- 20 minutes to assure the entire boiler and flue is "dried" out. You mentioned a 45- 55 minute run, which is great IF the boiler is above condensation temperatures during that run. (130-140° at boiler return)

    That temperature is critical to prevent condensation from damaging the boiler and also the flue piping connected to it.

    Corrosion or rust staining at the vent cap on the roof is also a good indication of the cold operating conditions in the flue.
    I don't see signs of corrosion under the diverter hood on the boiler, maybe it is getting up to proper operating temperatures?

    Not sure how much of the other corrections you want to make?:
    Confirm cir size
    Move cir or expansion tank connection to better location
    Eliminate bull head tee on supply above boiler
    Add some flow and temperature measuring gauges



    https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_16_na_0.pdf
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • newagedawnnewagedawn Member Posts: 549
    edited July 2018
    1 1/4 pipe into a tee with a 67,000 doe heating capacity????
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"
  • mikeg2015mikeg2015 Member Posts: 1,041
    Might consider just insulating the piping to conserve some heat, and then add some thermostatic radiator valves, and its a win-win. You save energy and operate the boiler right at the edge of condensing where its most efficient. Effeciency could be up around 88% depending on that boiler. Could check flue temps. Whether you condense in the heat exchanger depends on the approach temp of the cast iron sections more than just return water temp. Some big high mass commercial boiler can tolerate 110F return water without condensing because their just not that effecient to begin with.
  • unclejohnunclejohn Member Posts: 1,420
    edited July 2018
    Why not make the first tee above the pump a 90* ell and turn the by-pass into a full 1 1/4 primary loop and move the supply that used to exit the tee over and add a pump and make that the secondary. Maybe add a valve to throttle down the return.
  • DJDrewDJDrew Member Posts: 45
    edited October 2018
    All, just as an update...

    I am working on the suggestions of insulating the mains, modifying the bypass to pull more water and also looking to reduce the overall water that needs to be heated so return temps will increase faster.

    I called around to some local people about getting a quote to add TRVs to the first floor radiators so the overall mass of water that the boiler was trying to heat would be reduced. We have a wood burning insert often in use on our first floor, and it can keep the temp at a comfortable 73 most of the time. So the easy thought was to have those radiators automatically close off when the first floor is heated by the insert, yet the second floor where the thermostat is could still run as normal since the heat doesn't migrate into the upstairs hallway and bedrooms. Seemed simple given every radiator is piped individually to the mains in the basement? Well the opinions started flying...

    Two people that looked at the setup told me that the current boiler was "grossly undersized" and that it was "dangerous to operate" and that Slant/Fin would not stand behind any warranty on the boiler because it is undersized and because there is a bypass loop which is not specified in the install manual. Additionally, they said I am doing nothing but wasting gas by running this boiler with it being undersized. They suggested I have installed a 175000 rated boiler and to sue the original installer to get my money back on the original install. So this started a long conversation and math on the current EDR rating for the installed cast iron radiators in the house, a re-check of the heat loss, followed by phone calls to the local distributor, the local Slant/Fin sales rep and multiple calls to Slant/Fin corporate to get a complete picture/understanding of the situation.

    Heat loss: ~70,000
    Radiators EDR/ square feet of water: 947.1
    Slant/Fin Boiler rated square feet of water: 507
    Slant/Fin Boiler output (IBR): 76,000

    In talking with the local rep, local distributor and corporate. They all suggest that boiler is undersized, but that it is not a problem. They also said that because the boiler will satisfy the thermostat, a larger boiler would just satisfy it quicker - not really much if any savings on the gas bill from a larger boiler. That said, they all think the important thing to do is ensure that there is a means or mechanism to keep the return water temperature higher; even though their manual does not specify a bypass loop, the corporate tech people I talked with said it would be good practice/common sense to have one given the cast iron load of the system. Additionally, they also suggest I have the "Circulator Hold" option enabled to provide enhanced condensation protection - even if it means the circulator will cycle on and off a few times at first.

    When I called the one doomsday-er back to tell them thanks but no-thanks on the 175000 btu boiler along with the lawsuit and that I talked with everyone and I'm just going to stick to the original plan of having the bypass modified and TRVs installed, I was called an idiot and all the people I talked with were idiots who didn't understand the situation and were not experts in the field and that the install and possible pipe modifications are dangerous could be condemned because it is not installed as according to the manual. I then double checked with Slant/Fin's engineering team (very friendly & helpful support people!) and they once again didn't see an issue with having a boiler bypass and TRVs on a handful of radiators.

    That all said, when I added up the EDR rating for all the radiators on the first floor, I came up with 500.5, leaving the boiler to heat a load of 446.6 + pipe loss. So since we burn lots of wood in our insert all winter long, I am confident that the heating load on the boiler will be significantly reduced if there are TRVs on the first floor. Additionally, with the bypass loop working better and added pipe insulation, even if I am not burning wood, the boiler will be living happier.

    Overall, I have to hand it to the Slant/Fin support/engineering and the access to the local reps. All were very helpful and spent lots of time asking questions and explaining out their reasoning.

    Does anyone have any opinions on if installing TRVs are a project that I as a handy homeowner should undertake myself? Or should I just call in the professionals?
  • SuperJSuperJ Member Posts: 557
    edited October 2018
    In a steam system you have to size your boiler to match the EDR of your rads, or you may be condensing steam as fast as you can produce it and may never heat the furthest rads. But in a hot water system, you just need to size the boiler to the heating load calculation. Or in other words you can put 250,000btu worth of rads in a house with only a 100,000 btu heating load, and simply supply it with 100,000 btu worth of heat. Your 250,000btu rads might actually turn into 100,000 btu rads if you lower the water temp far enough (similar to what you have going on). I think your boiler is likely sized very well. The guy you talked too was right when he said a bigger boiler would just shut off sooner, you'd still have a cold return issue.

    Over sizing a boiler is not really an effective or recommended approach to managing low return water temperatures.

    Adding the TRVs will add some extra control and comfort but I don't think they'll solve the low return problem. You'll likely reduce the flow (which raise the temperature delta on the boiler), but the return water temperature is going to be colder than ever since the rads will only take the flow they need. It nice to couple the TRVs with a delta P pump.

    You first need a way to decouple the load from the boiler while it warms up to a safe temperature, a thermostatic bypass valve can do this, or a electronic mixing valve. Stopping the circulator is the crudest way of doing this. The most elegant and effective solutions probably will require adding a electronic mixing valve with a SWT sensor, and a boiler return sensors, and second circulator (one for the boiler and one for the zones).

    Coles notes: don't do the TRVs until you've fixed the return water issues in the boiler room. And don't fix it by installing a bigger boiler, your boiler is fine.
  • DJDrewDJDrew Member Posts: 45
    edited October 2018
    Thanks @SuperJ - your insight is helpful and reassuring! I'm hoping to get as much done at one time when the system is drained, including modifying the existing bypass.

    The two quotes I have been asking for on the bypass are 1) a basic temperature controlled 3way mixing valve on the bypass. Or 2) if it is not ridiculously expensive, go for your Cadillac solution mentioned above.
    With a pump dedicated to the loads, a 3 way valve (OA Reset and Boiler Protect functions), and a boiler dedicated boiler pump: All the rads will get flow right away, and the SWT will warm up gradually as the boiler RWT comes up to temp resulting in smooth even comfort, and worry free boiler operation.
  • Jason_13Jason_13 Member Posts: 297
    What is the delta-t through the boiler? May have too much flow which takes much longer to heat up. Been at this 40 years and I never use system bypasses always full size boiler bypasses adjusting the boiler to a 35 - 40 on large water volume systems. Never had a problem with Condensation on old gravity converted to pump system. Fast forward 5 - 10 years no rust on casting.
    Option two p/s again higher delta-t on boiler just as successful. Slower flow in boiler better mixing with existing boiler water.
  • DJDrewDJDrew Member Posts: 45
    edited October 2018
    Jason said:

    What is the delta-t through the boiler? May have too much flow which takes much longer to heat up. Been at this 40 years and I never use system bypasses always full size boiler bypasses adjusting the boiler to a 35 - 40 on large water volume systems. Never had a problem with Condensation on old gravity converted to pump system. Fast forward 5 - 10 years no rust on casting.

    Option two p/s again higher delta-t on boiler just as successful. Slower flow in boiler better mixing with existing boiler water.

    Good Question.

    So it finally got cold enough to let the boiler run for a little bit today. After about 30 min, the delta on the boiler was about 9-10 degrees difference.
    Supply Output: ~124 degrees
    Return before the 3/4" bypass: ~100 degrees
    Return after the bypass: ~114-115 degrees

    There are some rudimentary balancing valves on the front and back of house main supply/return lines before they combine and come down into the boiler. Currently, these valves are all slightly throttled to favor the rear lines (which have more radiators) and to slow the flow some so more return water is pulled through the bypass. If everything is wide open, the delta changes to ~15-20 degrees.
  • hot_rodhot_rod Member Posts: 12,025
    has nothing to do with delta, everything to do with return temperature. For oil, above 120, gas above 130 within 20 minutes or less is better.
    Delta can be at any temperature range, it does not assure proper return.
    Most boilers start from a cold temperature

    Bypass Piping was more for thermal shock, as it doesn’t assure return temp
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • DJDrewDJDrew Member Posts: 45
    Thanks @hot rod ...most reasonable cost solutions are coming in to install the Danfoss ESBE for a full 1-1/4" bypass. Would you recommend the 122, 131 or 140 degree element? I am thinking the 131 based on your comment and the water-mass of the system, but it seems to have an 18 degree opening pattern, so it would never fully open until 149 degrees, whereas the 122 element would be fully open by 140 degrees.
  • hot_rodhot_rod Member Posts: 12,025
    I started with a130 in mine, but the wood boiler started ramping down too quickly I went with a 115
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • VoyagerVoyager Member Posts: 224
    Since the original installer seems to have generally done a good job, have you called that installer to voice your concern with the RWT? I think I scanned all of your comments and didn’t see mention of this. Since they are familiar with your system, they might have a good recommendation to address this.
  • DJDrewDJDrew Member Posts: 45
    edited October 2018
    Hey @Voyager I actually had a good conversation with the original installer earlier this week. They were not concerned with the return water temp, only thermal-shocking the boiler. That said, I did discuss the Danfoss valve to help regulate the return temperature... they said they'd have no problem installing that valve. The original installer also thought a variable speed pump might be helpful too.

    I think for now, we are going to focus on modifying the bypass with the Danfoss ESBE 122 or 131 element. Labor wise, they think it would probably take about an hour if I do some of the prep.

    Slant Fin also alerted me to two documents (A, B) that confirm what everyone here and the reps have mentioned, which is very reassuring.
  • hot_rodhot_rod Member Posts: 12,025
    Here are a bunch of viable options for boiler protection piping. If you use VS circulators in setpoint mode, this piping method assures protection.

    These slides are from tomorrows webinar on Boiler Protection. mode.

    The second slide is an example for maybe a gravity conversion with a lot of mass, piping content and cast iron radiators. It also adds the ability to use ODR on the boiler loop circulator, and a delta P circulator for zoned radiators. A good way to blend all the latest pumping logics successfully.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
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