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gravity conversion piping

Paul Pollets
Paul Pollets Member Posts: 3,656
The best way to pipe a gravity conversion with a cast iron boiler is to use 4 way motorized valve connected to the proper control. We use a Tekmar 362 and ESBE valve and motor, and a sensor on the boiler return, to give absolute boiler return protection. The 4 way mixing valve should not be oversized. We always add TRV's to the radiators during conversion to properly balance the system.

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  • Paul_87
    Paul_87 Member Posts: 37
    Gravity conversion

    Does anyone have a scetch of how they pipe a new boiler in a converted gravity system? I always have done them with a primary loop and take the main house off as a secondary loop. I thought this was a good way to protect the boiler from cool return temperatures. Then yesterday I was on the phone with Burnham tech service and the person I spoke to said that Primary secondary piping does very little for boiler protection, which confused me because I thought that the main purpose for a primary secondary set up was to protect the boiler. He said he would fax me a scetch of a better way to pipe it but I never got it. So basically I need a new way to pipe it other than using a condensing boiler which the customer did not want to pay for. Thanks for any responses.
  • Mark Custis
    Mark Custis Member Posts: 539
    Need more input

    The last one I did was a very small home, and I left it gravity. I had worked on the system before, and knew the natural "flow" of the system to be very good.

    I installed the smallest CI I could find with the largest tappings, (somewhat of a trade off here). I put the pump that came with the boiler in my truck.

    Works very well.
  • murray renshaw
    murray renshaw Member Posts: 1
    gravity system

    Mark, I just converted a gravity system to circulating hot water. After some debate with my son Jim, we decided to pipe the new boiler using 1 circulator-(there were 2 existing supplies and 2 existing returns existing. We debated changing to a 2 zone system, but decided against it- Circulator sizings was important but I found all the information I needed at:http://www.oldhouseweb.com/how-to-advice/gravity-hot-water-heating-continued.shtml-I think the most important part of the installation was the by pass- WE fired off the utica 150 gas boiler and our customer has been warm and cozy ever since- In retrospect, I wish we had used a condensing boiler but was hesistant to do so- regards from new london ct murray renshaw

  • If using a conventional boiler, likely the safest (to boiler) and most efficient way is using a single circulator and a supply mounted thermostatic bypass valve type TV. Up to about 140F, all of the boiler flow will bypass the system right back to the boiler return and the boiler will come up to temp rapidly. Once that temp is reached, more and more of the supply will head to the radiation all the while ensuring that the return and boiler temps stay up where they should. Since the TV valve is both thermostatic and proportional proper temps are more assured than with primary/secondary. While the TV valve costs some (similar to another circulator) and it won't be consuming electricity for the rest of its life...

    If using a condensing/modulating boiler (they THRIVE driving gravity conversions), you usually must use primary secondary unless you also install TRVs on ALL radiators whereby in most instances and with most mod-cons, you can use only one circulator. It's the non-existant head loss at typical flow rates that allow you to omit primary/secondary. You must though include a differential pressure bypass valve so that you still have sufficient flow through the boiler when most or all of the TRVs are satisfied.

    TRVs don't come for free either, but they do allow amazingly effective "zoning" in each and every room without changing the piping, adding circulators/zone valves or even adding wiring for thermostats. As long as none of the rad branches are larger than 1 1/4", the TRV valve bodies are direct replacements requiring no piping changes. The major reason you need the TRVs is the nature of gravity piping which finds the least head loss to the lowest, closest rads and the greatest head loss to the highest (and usually farthest)--the EXACT opposite of piping designed for forced flow. Gravity systems usually achieve decent balance when converted to forced flow because the circulation rate is FAR higher than under gravity. No problem with a conventional boiler (especially if you use thermostatic bypass or primary/secondary), but essentially impossible with a mod-con.
  • Reverse the returns

    and then pipe it right through. I have installed hundreds of cast iron boilers and have yet to see one go bad from flue gas condensation. The original gravity boiler didnt have to come up to temp. Im talking gas here I have limited experience with oil except how to rip them out. One thing I always do is reverse the returns. The only flue gas failures I have seen are from the oversized pilots on the old bryants they condense on the casting all summer long and finally after 30 years eat a hole.
    If you feel you must , pipe in a boiler bypass but dont lock all that heat up in the boiler with a thermostatic device. I just cant see bringing a 500 lb mass up to temp before releasing heat into the system.
  • Paul_87
    Paul_87 Member Posts: 37

    where can I find a piping to diagram?
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    1 pump or 2....

    Paul, The German way is to use 1 pump for both the system and the boiler. THe American way is to have one for the distribution loop and one for the boiler loop. Which method do you prefer, and why??

    Thanks, and Happy Holidays!

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • A good diagram

    is in Dans book PUMPING AWAY. Gravity systems were piped in 2 pipe direct return. To have any kind of balance in the system you need to make it a 2 pipe reverse return. Obviously if your customer didnt want to pay for the modcon he isnt going to pay for 4 way valves or TRV'S.
    I have found by going to the end of the return and snapping the 90 off and replacing with a T, then running it back to the boiler, dont forget to drop your pipe size, 1/2 the size and drop one pipe size...2-1/2" =1". plug the T to the first radiator on the old return and your done. If you dont reverse them you have a good chance of the rear rads not getting hot.
  • Paul Pollets
    Paul Pollets Member Posts: 3,656

    On Viessmann cast iron boilers, I use one pump and the 4 way valve. The Vitotronic control does it all. I install system bypass (with globe valve) in addition to the 4 way valve, if the water content is 3x more than the boiler water content (per Viessmann instructions)

    On American boilers, I use the Tekmar control and 4 way, with a return sensor. The control holds the mixing valve closed until the return temp sensor is over 140. Most newer boilers (including Buderus) want the 2nd pump for the primary loop. Thermal shock needs to be addressed, or the boiler will have a much shorter life expectancy.

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  • Paul_87
    Paul_87 Member Posts: 37

    So then it is true what he said that primary secondary does not protect the boiler from cool return temps? Or is it only in gravity systems because of the large water quantity and over sized radiation?
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    It will IF...

    If you shut down the distribution pump and allow the boiler pump to continue running, it will protect the boiler. If not, it won't.

    I prefer the use of the non electric TRV. I have NEVER seen signs of condensation on conventional boilers operated with the ESBE valve on the return. Don't forget to put a bypass around the TRV for fill and purge.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    Thermostatic devices don't \"lock up\" the heat in the boiler....

    They release it proportionally as it becomes available and protect the boiler from condensing. Telling someone to reverse the flow through the boiler without moving the controls to the outlet will cause the manufacturer to void your warranty, and will cause a boiler inspector to shut your boiler down and not allow it to restart until the piping is changed, or the controls moved so that they can monitor and control the outlet temperature of the boiler. Simply turning the controls down by 20 degrees F don't cut it either. Been there, seen that , tried it, and it STILL flashed to steam, especially with low flow conditions.

    Also, counter flowing a boiler does not stop it from condensing, it just moves it to where you can't see it (top of the flue section instead of the bottom). The boiler is still going to condense.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Mark

    I was telling him to reverse the returns, not the flow through the boiler. I dont know about you but I live in Reading Pa. We are about 50 percent hydronic, all mostly old gravity systems. I have seen them piped in all types of configuration and have never , never seen one destroyed by flue gas condensation. Even when the people want gravity back in we would use a Weil Eg series..no thermostic or four way valve. They only last 30 years or more. And a thermostatic trap does lock heat in the boilerespecially on a mild pring day when the heat needs to come on for a few minutes at night. At least the gravity system lets the hot water rise to where it can be used. There is so much bull flyin around out there because the maufacturers want to sell extras like termostatic valves on gas water heaters because we need to keep the water heater at 140.. ohh please. next one I take out ill split it open and post pics and then you can explain to me why god chose to spare this boiler from the flue gas devil. Been doin this to long Mark. And please dont show me a 40 year old boiler that died of flue gas, its like when your 75 and you drop dead noone really cares what did it.Yes there is all kinds of fancy stuff out there for people that have money but there are alot of people that dont have much money and still need heat. A Cast iron boiler with the returns reversed piped in a pumping away configuration is still a good buy. We all dont live where the money flows like water and the air is so thin people forget how to think.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853

    That hurt, but I'm a big guy.

    I misread your post regarding reversing the return.

    You actually go to the trouble of re-piping the whole system just so it is reverse return? Why not apply non electric thermostatic radiator valves and not worry about it? It would HAVE to be cheaper than re-piping the system, and you get energy conservation and increased comfort as well.

    But it is your customers, and they consider you the expert.

    As for the lack of oxygen, I'm a native. I don't get light headed...

    And as for the cast iron condensing issue, I don't make this stuff up... THe BOILER manufacturers do. Am I wrong to listen to them? It is after all, THEIR warranty.

    You don't need to show me pictures of busted up boilers. I've seen my share, and you know, the older ones have MUCH thicker castings, hence less failures. I've also replaced newer condensed to death boilers. No bull.

    To each his own.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Tony

    Do you pipe any type of bypass into the boilers you replace ? Most manufacturers specify at least a hand valve between the supply and return for large volume water systems .

    I'm in agreement with you . The old gravity systems we see have boilers with NO bypass at all . Worked fine for decades . But Mark is right . These newer , more efficient ( and thinner material ) boilers should have some protection from low water temps . Chances are they'll work fine without it . But that's a chance ( and a risk of a voided warantee ) some won't take . A simple hand valve bypass is cheap insurance .
  • I understand I

    do not type very well and it can be difficult to get my point across. I missed typing class in high school.
    But honestly Mark most of the gravity systems here are what we call standard city homes, very common in this area Reading ,Allentown, Lancaster all built around the coal is king time. They have the old coal windows in the front where the coal bin was and the boilers sit in the middle of the basement using a shared chimney, though most have a divider wall in the chimney. Many of them are the old Weil Mclain coal stokers converted to oil or gas. The gravity systems themselves are works of art. The fitters knew how to lay out their T's..horizontal, vertical, 45, so the flow would be balanced in the sytem and then when they were finished they would have the apprentice paint the pipe black and gold leaf the fitting beads, sometimes silver. Most are piped 2-1/2 mains though in some of the wealthier section of the old city you see 3 and 4 inch mains and we have our share of steam. Anyway it really isnt difficult to go to the end of the supply main and snap the cast 90 off the last radiator on line put in a T and just run 1" copper back to the boiler. When you work on these type systems you get really fast at snapping cast fittings and wicking on new adapters, sure sometimes you run into the crawl space deal but not often.
    I sell my share of TRV'S AND I always offer it as an option but for 3 floors of radiators that havent been touched by a wrench in over 100 years, Take my word for it, its alot more money.
    As far as the thermostatic device, I got my first copy of THE COLOR OF WATER when I was in apprenticeship school. They lock heat in the boiler that is why they put post purges on the new modcons, nothing new, gravity systems were post purging 100 years ago. Whenever we remove a tankless coil and install a seperate gas fired water heater we remove the triple acting(some dont) and open the flow valve just for that reason.
    Many systems are going to landlords where the tenents pay the heat, believe me they arent buyin modcons or trvs.But they will pay to make those radiators in the back room get hot.
    And a large portion of work today is going to retiries over 70. Hard to sell them on payback time or saving the earth speech.
    As far as the manufacturers go, I have the attitude...They need me, I dont need them. How many times do you have a problem and they make you feel like your the only one with this problem only to find out a month later its a countrywide problem and they knew it. They lie lie lie, Just in the past 15 years look at the problems. Little weight kits for flow valves,plex vent, ultra vent, polybutylene, aluminum liners, zone valves. telestats, on and on and on. I believe the big ones are soon to come, aluminum hx, come on this is a disaster waiting to happen and alot of good customers are going to move on. They say the national average is 7 years for people to live in a home but I dont believe it is those people who buy high end stuff and I think alot of guys are going to lose good customers over these Aluminum hx. Time will tell.
    I will start posting pics of old boilers that have been installed with no bypass and "boiler protection" and have lasted half a century. We all should, then we can really learn and not just take the manufacturers word as God givin truth. The truth shall set you free. I see what happens here, just like our politicians, They take some of the really sharp guys and hire them for magazine articles, now the magazine gets money from the advertisers, as a matter of fact the advertisers are the magazine. All of a sudden things arent so black and white, they are grey. Human nature never changes. They all monitor this website. But lets be fair, anyone can have problems, its how they take care of them that defines them. If a company does good then they should also get the praise. OK Im done.
  • No I dont

    When I replace cast iron boilers on gravity sytems I use either Weil mclain or Burnam I prefer Burnam because they are side outlet and they seem to lend themselves better for multible zones and the burnam uses a step valve on smaller units but both units have served me well. I have units that I put in with my father 30 years ago, that I maintain. I know that they could save money on a newer modcon but they arent going to replace it untill it leaks. And they aint leaking! as a matter of fact I open them up look down the sections, vacuum the burners, wax the jacket,check the chimney base and Im gone. Ive gone to schools and seen the pictures of horrors of flue gas and I have seen the flue gas eat steel flue pipe(remeber the first Weilmclain HE,s the instructions let you sidewall vent with galvanized pipe if you sealed the seam with silicon HAHA) I dont think the efficientcy has gone up except for the advent of the vent damper and they feel just as heavy (maybe thats just me) it would be interesting to see what changes cast iron manufacturers have changed in the last 30 years. Shipping weight and efficientcy would tell alot. Ive seen alot of systems that boilers were put in with a system bypass. Not a boiler bypass. Now they cut down the flow through the sytem and compounded the problem of not reversing the returns so ultimately they closed the vavle on the bypass. They are still in!Im not imagining this. I will get pics of all the boilers from 1 to 30 and older that i didnt put in. Maybe someone like Perry could explain why it doesnt effect them, something like excess air and co2 on cool cast iron surfaces, I dont know why but I know they dont need it.
    Its fun to watch those gravity system, even when it starts to get a little colder they rarely get up above 120, way below condensing point.
  • Dave Stroman
    Dave Stroman Member Posts: 763

    Here is an interesting way to pipe a gravity system. Let me first say that I need to credit this idea to Peter Caruso who works for Mestek and who reps the rAy boiler in the photos.

    Look at the photo of the piping and the crude drawing. It shows the 1 1/4" supply piping from the boiler being reduced to 3/4" and squirting, or injecting into the larger 2" piping. I causes a venturi effect that pulls a portion of the cold return water along with it. It sort of get the gravity flow going and once things warm up, it will almost flow by itself. On cold start up, you can tell that some of the water from the boiler simply bypasses the system and goes right back to the boiler. But as things warm up, gravity takes over and we get a good flow to the system. Although this does not protect the boiler from cold return water, it has other benefits. When the pump shuts off, the flywheel effect of the gravity does not stop and the system continues to flow. I think just a few degrees difference can keep things flowing. Many times I am trying to figure out how to stop gravity flow, especially when the indirect water heater is calling. But in this case, the check valve in the pump keeps the hot water in the boiler, and lets the system do whatever it wants. And since gravity it still paying a large part in the flow through the system, no real piping changes need to be done to the direct return configuration. Not that most of us ever changed that anyway.

    Just another interesting way to do things.

    Dave Stroman
    Dave Stroman
  • Timco
    Timco Member Posts: 3,040

    It is my understanding that a simple system bypass will provide enough mixing to protect multi-zone CI boiler converted gravity installs from cold return temps, and the ESBE type P/S setups are more for copper-fin boiler protection so nothing below 140* gets back to the boiler. If piped in P/S with no ESBE, is it not just another way of mixing cold return water with hot supply water? If one big zone, a bypass just heats the boiler quicker, but there really are no cold return temps as the system heats up as a whole.

    Just a guy running some pipes.
  • Paul_87
    Paul_87 Member Posts: 37

    That was also my understanding which is why I posted the question. I thought that a primary loop was a bypass but better. I am still waiting for someone to explain it.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853

    Your typing skills are just fine. It's my reading and comprehension skills that need tightened up. I was reading the Boiler Counter Flow Piping thread right before I read this thread and confused the two of them. My apologies.

    I also understand that not everyone can afford my services, and do not profess to close every job I see. I'm just trying to do the right thing, and understand that the right thing is not in everyones budget. Nor is my view of the right thing the same as everyone else's.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • R Mannino
    R Mannino Member Posts: 440
    Here is a diagram

    Just make the 2 fitting changes, simple as can be.
  • R Mannino
    R Mannino Member Posts: 440

    When you install your boiler bypass what temperature rise are you looking for in how much time? Where do you draw the line between short cycling the burner and time till you reach 180. You know another thing that is odd is even though those gravity systems run low temperatures I really hadnt seen much flue gas problems with chimneys on the old gravity systems, I see alot more damage with the advent of the flue dampner also even when the boilers are just starting and are below 100 degrees I never see condensate running on the floor.
    I know that when you have a well with acidic water from co2 and you boil the water it becomes neutral and if it was acidic and hard it becomes alkaline, maybe this is why the acid condensate doesnt harm the sections because the co2 is vaporizing out before it can do damage. I dont know, but I do know I beat enough of those old boilers out with a sledge hammer and they were not any thinner than 50 years ago. Just my thoughts.
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