steam boiler help

kevin_t

i had a contractor installed new steam boiler (one-pipe system), Weil-McLain EG/PEG Series 5, the old boiler was 150k btu, the new one was down to 140k btu, during cold weather, the boiler short-cycles, i have pressuretrol set to cut-in at 0.5psi, diff 2psi, the cycle looks like this:
1. fire for about 3-5 min
2. shuts off due to psi reach in the pressuretrol (builds pretty fast)
3. psi drops to cut-in in about 2-3 min
4. repeat

wondering what is wrong or is this normal during cold weather, i've replaced all radiator's vent valve, all radiators seems to be heated except the largest one in the living room, the large one seems to be half heated. the short-cycling is of concern

any help or tips would be appreciated, i have absolutely no experience with these type of stuff

bburd

That is normal operation for a boiler that is larger than needed for the radiation in your house. A replacement steam boiler is supposed to be sized according to the connected radiation load, plus a piping and pickup factor. 

Did your contractor measure all the radiators before sizing the new boiler?

There are other possible causes of short cycling on pressure. Do you have adequate main vents (typically installed at the ends of the steam mains)?

JUGHNE

Did the old boiler short cycle?
And as said above, does the steam main have air vents in the basement?

kevin_t

@JUGHNE @bburd

i don't see any steam main vent in the basement, but if the vents are suppose to let air out, then wouldn't the air vents on radiators do it?

i don't think the contractor measure anything, when the contractor came saw the old boiler and just said its too large, i guess he just estimated base on experience, from 150k to 140k

ethicalpaul

The radiator vents can do it, but you don't want them to. It is probably the biggest waste of fuel and cause of imbalanced heating that exists in the world of steam heat. Definitely get the main venting in order and much of your problem may improve.

If it it cycling on pressure, then your installer did you a disservice.

JUGHNE

The air vents on the radiators are there to only vent the air out of the radiators. They will vent all the air, but they are very small compared to steam main air vents which are to get the majority of the air out of the main piping.
The quicker the main is vented, the quicker the system heats.
More fuel is required to push air out of the system if the venting system is lacking.

Vent mains fast and rads slow is the rule.
Lack of main vents can contribute to short cycling.

If you can hear the water that implies you probably have slow condensate returns.

New boiler piping install may have changed things to give you new problems.

Could you post pictures of the boiler to include piping floor to ceiling, from each side if possible?

kevin_t

could the main vent be inside in the wall?

Jamie Hall

That type of behaviour -- which can occur whether the boiler is oversized or not, but is going to be worse if it's oversized -- is almost always indicative of either no main vents or badly undersized main vents.

On a one pipe steam system, you really need one main vent -- depending on the size of the system, either a Gorton #1 or #2 -- at or very near the end of each steam main, after the last radiator takeoff.

JUGHNE

The reducing Tee in the horizontal pipe just above the boiler (header) is preventing the header from draining down the pipe to the bottom of the boiler (equalizer pipe).
The header is meant to drain any water down the equalizer back into the boiler. Is the header sloped to drain towards the tee?
The header should remain full size horizontally and then may be decreased only after turning down.

Find the install book for your new boiler and look at piping diagrams. That is the minimum piping/sizing requirements.

We need more pictures of the floor/lower piping to determine more. What is the red circle indicating?

kevin_t

the red circle i'm not sure what that is, maybe is the vent?

JUGHNE

Just a added note on the equalizer connection. Any reduction of the pipe must be done in a vertical pipe.....

It looks like you have wet returns. One iron pipe is coming thru the wall and then there is a copper connection coming from the valve with the blue handle. Where does the copper into the blue valve come from?

Somewhere at the other end of the wet return(s) the pipes come up out of the floor and drain the steam main condensate water back to the boiler.
At that junction is where your steam main vents should be.
If the basement is finished, the vents if there, may be covered.

kevin_t

the blue handle is basement return pipe, basement is heated by water

but regardless, the boiler should not cycle off pressure correct? probably need to find another contractor to fix the issues

JUGHNE

Does the short cycling coincide with you using the basement heat? FWIW, you are pumping into your Hartford Loop.
That connection would usually be directly into the boiler.
The old and new boiler water lines may have been different.

Was this boiler ever skimmed? Just to the right of the sight glass is a plug that would be the skim port. It looks untouched.

clammy

Poorly piped and yes to finding another contractor aside from possible need for main vent it’s a poor example of how to-pipe a steam boiler . Take a look at the manual . Find someone who will pipe it using both tappings and set it up for future cleaning of the water side of the boiler . Peace and good luck clammy

kevin_t

when it short cycles, the basement pump was not on, basement usually a lot warmer, the thermostat in basement never really kicks in

i don't think the contractor skimmed the boiler

JUGHNE

As what Clammy said about piping at the boiler, if you look at the install book you would see if your size needs 2 risers and the pipe sizes needed.
The tee in the header is an obvious problem and if corrected the system, while not piped correctly, might behave.

Between and skimming things should improve.
Some homeowners who find this incorrect piping might confront the installer with the book and request corrections be made.
It is surprising he thought your old one was too big.

bburd

@op much of this discussion might seem a bit cryptic to you as a homeowner. You might want to pick up a copy of Dan Holohan‘s book “We Got Steam Heat!: A Homeowner's Guide to Peaceful Coexistence”.

Contractors who understand steam heat are hard to find these days. Where are you located? We may know someone in your area who’s well qualified. 

kevin_t

@bburd NYC

bburd

There are some good people there. @JohnNY is one of the best. Try the “find a contractor” feature of this site.

JohnNY

Thank you for recommending me but that's a mess and I'm not touching it.

bburd

@op as you can see, the folks who post here are very knowledgeable and passionate. They also tend to be perfectionists.

We see far worse near-boiler piping than you have on this board every day. If the short cycling is the only problem, the system heats evenly and quietly and the vents don’t spit water, the piping probably does not need to be changed unless the manufacturer requires two risers on that size boiler. “If it ain’t broke, don’t fix it.”

Regarding the short cycling, it’s an extremely common problem; many if not most home boilers are oversized. It reduces fuel efficiency a bit, and causes a little extra wear on the moving parts, but there is no need to lose sleep over it.

You should probably reduce your pressuretrol differential setting to 1 rather than 2 though, since these systems run best at 2 psig or less.

Do look into your steam main vents since they are crucial to fast heating, fuel efficiency and quiet operation. Good main venting will also minimize short cycling near the start of the heating cycle.

Your system certainly would benefit from insulation on the steam pipes (there is no need to insulate the returns); 1 inch fiberglass is recommended, and you probably won’t find it at the big box stores; you can get it from supplyhouse.com or other online suppliers. 

kevin_t

@bburd i have a finished basement, the main vent is probably covered, i can't seem to find it anywhere

what i've noticed these few days is that the short-cycling happens mostly on colder days.

on colder days:
during a cycle, i noticed the pressure reaches 2-3psi first and shuts off before all rads get heated, the largest rad stays cold though, without all pipes filled with steam or air, the pressure shouldn't build up is my understanding, not sure if that's correct, but the fact that the pressure builds up first is telling me the air inside the pipes aren't getting out

on normal cold days:
during a cycle, this is much normal, it would fire for about 10 min, all rads gets heated, thus satisfies thermostat, pressure stays at 0

any ideas?

bburd

It is normal for pressure to build eventually if the boiler is oversized, but only after all the radiators are heated. Unless you have more than one steam zone, or the boiler is *severely* oversized. 😱

It sounds like your main venting at least is inadequate. You want to vent the mains quickly, and the radiators slowly, for the system to operate well. (Slow radiator venting prevents condensate from developing fast enough to cause problems like uneven heat distribution, water hammer and spitting vents).

Main vents are normally installed at the ends of the steam mains, after the last radiator runout. Sometimes this is far from the boiler, and sometimes the mains circle back to the boiler room and the vents are installed near the boiler.

If there are homes similar to yours nearby with steam heat, built around the same time, that have unfinished basements, you might be able to see where the main vents are located.

There are formulas for determining the correct main vent capacity based on the length and size of the steam mains. A search of this board should find them.

Jamie Hall

As @bburd says, if your pressure is building before the radiators are hot -- you're main venting, if it's there at all, is woefully inadequate.

I might add that allowing it to build to 3 psi is too high, and may be making the situation worse.

motoguy128

When a steam system is heating three things are happening.

1) Heat is being produced by the boiler.
2) Heat is absorbed by the steel and iron. 0.11 BTU/lb-F. That’s 1650BTU per every 100lbs that are heated by 150F. 5000lbs would consume 82,500BTUs. This is part of the reason boilers have a pickup factor as part of the sizing.
3) Heat is emitted by the heated metal.

On cold days, the main and some radiators are likely fairly hot when the system comes on, while the radiators that never heat up are still cold. This means the warm radiators heat up even faster. But colder radiators are still limited by the vent rate and steam will tend to be limited by the size of the lateral and pitch of the pipe and radiator all else being equal.

I also suspect your boiler is oversized. But if main venting is fast, you can still balance a system. I previously had a boiler 30% larger than the total EDR. It ran <3oz. My current boiler is undersized by about 30% but I’m using TRVs. It was running around 0-1oz, but Lately it runs around 6-8oz. (probably needs skimming again)

Steamhead

@kevin_t , which model EG/PEG?

Where are you located?