New boiler, short cycling

lewislin · November 2019

Hi,
Been reading to the site and found the steam system is fascinating. We just replaced an old, leaking boiler with almost identical model Lennox GSB8-E 150K BTU. It's inside a 1500 sq ft house with 5 radiators. (There are signs that previously owner took out couple radiators.) The old model was working fine before the leak so the contractor put in exact the same model. However, with the new one, I noticed that the boiler would reach the cut out pressure (0.5 cut in, 1 diff) in 1 minute. Every radiators in the house are hot. I suspect maybe somehow the new boiler is running more efficiently and might be oversized for my system. Does this analysis make sense? Actually hoping that I am wrong and there is some way to fix this.
Thanks,
Lewis

acwagner · November 2019

You can calculate whether your boiler is oversized or not. It's a straightforward calculation.

The size of the boiler required is dependent on the capacity of the radiators. This link has a rough worksheet to calculate the output (in square feet EDR) of your radiators.

http://www.smithfieldsupply.com/company_info/forms/radiatorest.pdf

Use the sheet to sum up your all the EDR of your radiators. 1 square foot of EDR = 240 BTU/HR.

Your boiler should have a plate on it that states the rating for steam. If not, find the manual for your boiler and it should have a table listing the output rating.

If you're having trouble working it out, post some photos of your radiators and your boiler rating and someone here can help you out.

From your general description, it sounds like you are oversized. But, the calculations will say for sure.

KC_Jones · November 2019

First, a replacement boiler should never be sized from the old one and in my opinion, on steam, it's not hard to calculate the proper size so there's no excuse to skip this step.

With 5 radiators and that size boiler, unless the radiators are absolute monsters you are most likely over sized. If you want to figure this out we can help you calculate the appropriate size with some info, can circle back to that if you are interested.

Next thing, was the new boiler skimmed by the installer? If not that could be the source of the fast pressure cut out. Surging due to excess oils in the water can cause sudden and dramatic pressure increases causing the boiler to cut out.

The venting on the system could also be contributing to this, even if the old boiler was functioning reasonably well. Do you know what the main venting is like in the basement?

Could you post pictures of the install? Sometimes poor piping can exasperate the problem and it would be good to see what's going on.

Fred · November 2019

The boiler is probably well over sized but you don't need to guess. Measure the EDR of each of the five radiators, add them together and then compare that number to the Sq. Ft. Steam number stamped on the boiler plate. You can find EDR tables to measure the radiators anywhere or post a picture with the height, width, number of sections and if it is column or tube style and we can help you.
BTW, It's never a good idea to match the size of an old boiler.

Jolly Bodger · November 2019

old boiler could have been derated.

lewislin · November 2019

Thanks guys! I had previously no knowledge of the steam system. I only start learning all these after the new boiler was put in last week. And the more I read, the worse I feel. I will measure the EDR and report back later when I get home.
The boiler was skimmed by the installer. He even used some TSP powder to clean the system which was really dirty.
I believe there is no main vent in the basement. Will post picture later as well.

EdTheHeaterMan · November 2019

A leaking boiler will have longer run cycle. if the steam is leaking out a small opening somewhere, the pressure will take longer to reach the cut off point. With the new boiler (no-leaks) the pressure will build up fast.
You may need to follow @Jolly Bodger advise and derate the new boiler to match your load.

I hope it is not Too much oversized

ethicalpaul · November 2019

If there’s really no main vent that could be a silver lining for you since adding one is very doable and may help your cycling significantly.

You may also be able to add back some radiation improving comfort and sizing

lewislin · November 2019

Hi Thanks for all your help. This is such a WARM place!

I hope I understand correctly. The EDR comes out as 153.75 which is 36900 BTU. My boiler as 150K is about 4X oversized?

Boiler room:

KC_Jones · November 2019

That boiler piping is absolutely the wrong size and is definitely part of the problem. Choking the outlet down like that, especially on that style boiler is killing the performance.

It’s too bad you paid for this already. It’s really sad “professionals” are doing this.

Your contractor IMHO needs to do 1 of 2 things, either learn how to do it properly, or never touch steam ever again.

Also steam shouldn’t be piped in copper.

Step one, get the boiler piped correctly, properly sized would be good too, but I’m sure the contractor won’t fix that. I’d speculate the piping will be a stretch as well, if they are even willing to do anything.

After that you might be able to get passable performance from it by working on venting and balance.

You probably aren’t 4x, more like 2.5x. For that EDR you basically needed the smallest steam boiler made and it would still be on the big side.

JUGHNE · November 2019

At least it looks like the outlet tee is 2 1/2" then reduced to 2" copper. And a skim port is added.
This should probably use both outlets...the one on the other side is plugged. Now would be the time to try to get that plug out before steam welding sets in. If out, then just a 2 1/2"nipple and cap would be a good head start for the future.

But who knows what is above the ceiling....bullhead tee?

lewislin · November 2019

To be fair to my boiler guy, he did ask me if my original boiler was running okay before it leaked. I answered yes because it was indeed running smoothly. He also mentioned the piping was not ideal but since everything was working he did not intend to change it.
Sigh.. But after the new one, I started to hear the hammer noise and short cycling. That is what prompt me to do the research and found this site. Again it is still fascinating to learn all these knowledge. Wish I had know this earlier.
Saying that is there someway to remediate the situation? I read about down firing the boiler, is that something available for my boiler? @ethicalpaul mentioned main vent, would that be enough to handle this big difference? @KC_Jones do you mind elaborate what piping changes need to be done?

EBEBRATT-Ed · November 2019

You only needed a boiler with about 60,000 btu input.

BobC · November 2019

Does the water in the sight glass move up and down a lot? If it's more than + / - 1/2 inch it may need more skimming. If it quiets down after being skimmed that was the cause of the noise.

That looks like a atmospheric boiler and if it is the gas can be turned down some. It would still be oversized but less so.

Bob

ethicalpaul · November 2019

That is significantly oversized. Your installer really did you no favors, as explained by @KC_Jones. I'll just answer about the main vent as you are going to have a lot of info coming your way

I don't think the main vent will solve your oversize problem, it's just too much boiler for 5 little radiators. But you should still find out if you have one because at least it will help your system run as well as it can.

It's going to be a challenge if the whole basement is finished like I see here because the main vent (if any) might be above the ceiling.

You want to follow the pipes around your basement wherever you can, noting places where you can see "risers" coming off the main pipe going to your five radiators (and you may have some abandoned ones that are capped off).

After the last radiator coming off the main should be a place where the main turns to go to the floor. It may be that 45 degree copper pipe I see in the background of your photo. This is where the main becomes the "return". Somewhere between the last radiator branches off and where the return starts is where the main vent should be. But based on what I see in the photo it would not surprise me in the least if whoever installed all that copper never put one in. But look for it!

KC_Jones · November 2019

> @lewislin said:
> To be fair to my boiler guy, he did ask me if my original boiler was running okay before it leaked. I answered yes because it was indeed running smoothly. He also mentioned the piping was not ideal but since everything was working he did not intend to change it.
> Sigh.. But after the new one, I started to hear the hammer noise and short cycling. That is what prompt me to do the research and found this site. Again it is still fascinating to learn all these knowledge. Wish I had know this earlier.
> Saying that is there someway to remediate the situation? I read about down firing the boiler, is that something available for my boiler? @ethicalpaul mentioned main vent, would that be enough to handle this big difference? @KC_Jones do you mind elaborate what piping changes need to be done?

I’m going to be brutally honest, he really shouldn’t be asking questions of you like that. He should be explaining to you what is proper. You just calculated the size on your own, a step he apparently couldn’t be troubled to take. The manual for that boiler has a picture and pipe sizing listed as a minimum spec for the boiler, you do not have that.
I attached a picture from the manual that came with the boiler showing what is proper, your configuration appears to be ok, but it's the wrong size so it isn't per minimum spec. The manufacturer could void your warranty for that one reason, if a warranty ever comes up. Also ditch all the copper.

I doubt very seriously if you will get the contractor to change to the correct size boiler, and getting all the piping redone properly might be a stretch, unless you are willing to cough up more money, which IMHO you should not. Smaller boiler with correct piping should have probably been the same price you paid. We do not discuss pricing on this board so please don't quote any numbers.

Looking at Lennox boilers, and using your numbers, the smallest one would be about 28% over sized using current standards. The one you have is 150% over sized.

I'm sorry, but it makes me sad that there are people out there willing to take money from people and do things so wrong.

ethicalpaul · November 2019

For comparison, here is a nice small boiler in an excellent installation posted recently by forum regular @EzzyT

Note the correct use of black iron threaded pipe and an appropriate size boiler that was determined by Ezzy using the same radiator calculation that you used. Don't despair too much, it is likely you can get things running pretty good.

https://us.v-cdn.net/5021738/uploads/editor/jv/mduj5k8oleni.jpeg

Fred · November 2019

@lewislin , Look at your boiler plate and tell us what it says for "SQ. FT." of Steam. The boiler also needs BTU's for another 33% of piping and Pick-up factor and people get confused on boiler size using just the BTU. The boiler is too large, the question is by how much and then we can make suggestions on how best to tame it. Main vents are fine, but they close when steam hits them and that's when pressure builds. Down firing may help, if it's possible on that boiler, may help. A two stage gas valve, running on low fire may work, again if it is possible on that boiler.
As @KC_Jones said, the best option is to get the contractor to come back and replace the boiler, with the properly sized one and re-pipe the near boiler piping. Having said that, he most likely did not charge you to do any re-piping and you and he may have agreed it wasn't, in your opinion necessary. Well Lesson learned.

wz25 · November 2019

I sympathize with your situation, because it sounds a lot like ours. Moved into an older house that converted from coal to gas some time ago, similar size to yours. Original boiler was never properly piped, and had a leak; started spewing steam from the back in the middle of winter, so our HVAC installer put in a new (same model and size) boiler, following the original (incorrect) piping, and converting the near-boiler-piping to copper, to boot.

We had about 150-160 sq.ft. compared to the boiler's 308 sq.ft. rating. Never experienced hammer, but had very wet steam. Radiator vents would pant, and I could hear gurgling in the runouts/radiators. I had to skim ad-nauseum just to keep things kind-of working, and it the cost of replacing vents that were constantly getting waterlogged was starting to add up (not to mention the inconvenience of waking up with a non-functioning radiator due to a dead vent).

Ended up having one of the pros on this site ( @Dave0176 ) re-do the near boiler piping, downfire (Peerless 63-03 --> 63-03L via manifold swap), adjust gas input, install a new runout to addition, add two big-mouth main vents, and a host of other tweaks.

There was no way around this, and while it was far from ideal to have to do extensive work less than a year after the new install, we figured it would have to be done eventually, and there was no point in living with a sub-optimal heating system any longer than necessary.

lewislin · November 2019

@Fred I found the boiler's sq ft rating is 383. like @KC_Jones was saying 150% oversized. Oops...

>It’s too bad you paid for this already. It’s really sad “professionals” are doing this.
@KC_Jones My feeling about the "professionals" generally in the decade of my house ownership. Within the week of my quest to understanding the steam system, I feel like I learn so much that I almost want to be an apprentice of this industry and get hands-on experience. Saying that, I guess this also apply to many other professional too - lawyers, accountants and etc. Once a while I will meet someone who is really enthusiastic to what they are doing and it feels really good talking to them. Those kind of person almost always eager to teach and share. That is also why despite my own misfortune, I am kind of happy that I found this community, where people seem to be really enthusiastic.

@wz25 it sounds exactly like my situation. Glad you were able to make things right in the end! It must feel so good when everything is running correctly according to the spec.

@BobC As far as I can tell, the water is clean and it is not moving up and down too much. I will need to observe more for sure.

@ethicalpaul Thanks for detail explanation of main vent and the picture of that black iron threaded pipes. They do look really sturdy and powerful!!

I like what Dan Holohan said in one of his speeches. We figure out the engineering problem. Now it is time to figure out the sociology part of it, ie, talking to my contractor... The heater is sort of working. My house is warm. I am not sure about calling him and saying to him that he gave me a wrong size of boiler will get me anywhere. I most likely need to pay some tuition on my own. If you guys have some suggestion on the sociology part, that is welcome as well.

KC_Jones · November 2019

The boiler needs re-piped, IMHO you have no hope of getting it to run correctly until that is done. After that you will have some hope of getting it to run correctly with proper venting and balance.

Also there is a slight possibility you will have to run the pressure slightly higher than we normally recommend to ensure you get enough run time to distribute the steam. That all depends on how much the venting will overcome on building pressure.

New boiler, short cycling

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