Inadequate venting/High pressure?

sibellc

Hi,

I help manage a small pre-war coop in NYC with one-pipe steam heat. Having just started up our boiler for the season, and having done a lot of reading on here, it seems that our system maybe poorly designed. At start-up, it took about 20-30 minutes for the pressure to start climbing. I could only see two small main vents.
One of the main vents hissed the entire time. The pressure appears to be set to 5psi. During this time, the automatic water-fill valve activated.

Last heating season, I've been around the boiler and it seems to fire about 3 minutes at a time before cutting off at 5 psi. When I've been in other people's units, I heard hissing from radiator valves for several minutes at a time.

Assuming no one in the building is experiencing comfort issues, is this operation particularly fuel inefficient? For the three coldest months, we consume 1,400 therms a month to heat about 12,000 square feet.

Thanks!

Steamhead

I'd say that system needs some professional attention. There are plenty of Steam Men in NYC- try the Find a Contractor page of this site.

gfrbrookline

what @Steamhead said.

Your NBC is a mess and the main vents are slightly upgraded radiator vent. Your operating pressure is way to high which means most of the radiator vents are toast. It should operate at 2 PSI max, most run at 1.5 or below. Radiator vents usually fail after 3PSI. If the main vent hisses through the heating cycle and doesn't close it has also failed likely due to the pressure setting as well.

Your entire system needs to be evaluated, as @Steamhead said try find a contractor on the site. @JohnNY comes to mind as an active member of this site who may be able to help.

ethicalpaul

> At start-up, it took about 20-30 minutes for the pressure to start climbing.

It sounds like you may be under the mistaken impression that building pressure is a desirable thing

mikeg2015

Boiler is probably oversized to load so if you drop the pressure it just short cycle unless a 2 stage control was added.

The gas bills seem a little high for multistory for that size building but not too far out of line. A few adjustments and a proper service of the boiler might pay for itself.

mikeg2015

I see 3 pressure controls. Wonder if it already has a hi-lo setup. Plus a backup limit since it’s commercial.

I notice the main gauge has a vacuum range. I wonder if it originally was a vacuum reset setup. Or the contractor just uses those on all installs.

sibellc

I’ve learned from here that building pressure is not a desirable thing - it was merely an observation as to the current state of operation.

If the current pressure settings are destroying the vents, and the boiler is sufficiently oversized that it has to be set that high (an interesting catch-22), can sections be removed from it to reduce its Btu output? It has an input of 910 mbtu, a gross output of 724mbtu and a net output of 543 mbtu.

As far as controls, in addition to the three on the front, there is a pressuretrol mounted on the back, and an ancient looking device called a “fuel watchman”

Thanks for your help.

ethicalpaul

> I’ve learned from here that building pressure is not a desirable thing - it was merely an observation as to the current state of operation.

OK cool, I always have to check

> If the current pressure settings are destroying the vents, and the boiler is sufficiently oversized that it has to be set that high (an interesting catch-22),

I hope no one said that the boiler is oversized therefore you have to set your pressure too high, because that wouldn't be correct I think.

What they might have said is that an oversized boiler is likely to be short-cycling a lot, which may be unavoidable, but can be minimized with good main vents. Cranking up the operating pressure is not a solution.

Some boilers can be modified to fewer BTUs but it's probably not a DIY project! Curious, what model do you have?

sibellc

It is a Weil-Mclain LGB-8 installed in 2006. No, I would never execute any work as a DIY - we do everything by the book. I may have misread one of the other poster's comments re: dropping pressure causing short-cycling.

tkos115

What I think they mean is that it may be an over sized boiler for the application. If it is, that would explain why the pressure was set so high. If it were to be set lower, it would cause it to short cycle.

ethicalpaul

sibellc said:

It is a Weil-Mclain LGB-8 installed in 2006. No, I would never execute any work as a DIY - we do everything by the book. I may have misread one of the other poster's comments re: dropping pressure causing short-cycling.

From my reading of that boiler's manual, it does not have a lower-capacity version with which it shares the number of sections but has a different number of burners (if it did, that would imply that you could install the smaller burner kit).

As it is, you could have a technician come over who was willing to consider blocking off a couple burners and/or trimming down the gas pressure and then testing the combustion to see what could be done while still keeping safe combustion numbers.

But get the main venting ship-shape first, because after that, the other problems might evaporate

Jamie Hall

An oversized boiler which doesn't modulate the firing rate will short cycle once the system is full of steam. It's the only way that the steam produced can be made to match the steam consumed. There's no magic about it.

Furthermore, it will do that regardless of the pressure settings. All higher pressure will accomplish is to burn more fuel raising the pressure.

There are, however, other ways to control the cycling. Several people on the Wall have had good success with controlling it with timers, although this can be a bit finicky to get right, rather than depending on the lowest set pressuretrol or vapourstat to be the controlling device. Though I prefer using a vapourstat as the controller, it's more of a philosophical preference; I expect that if I were dealing with a really seriously oversized boiler, I might at least put a time delay on the restart...

Fred

It must have a two stage gas valve on the boiler. The Pressuretrol on the back is a manual reset (red button). I'd trace the wiring to the three pressuretrols on the front and see where they all go.

neilc

those main vents look old, and tired,
and could be improved upon.
then the rads also.

I would also be checking all those pigtails,
and that tree they're mounted on to be sure it's all clear,
and that the trols are seeing boiler pressure.
maybe the gage is out a bit, but the #1 trol looks set around 1, and that's where you would hope your gage should top out.
what are the differential wheels inside the trols set to ?

like others said,
find a contractor, John, or a couple other locals that visit here.