oversized boiler

greengiant

I'm trying to find a way to compensate for my oversized boiler. Currently it cuts out for pressure then cycles back on numerous times during a call for heat. I have 270 square feet of radiation but the boiler can handle something like 450 square feet. I was thinking about replacing my vent-rite #1's on all radiators with something that has a larger orifice for faster venting. My reasoning is that if each radiator vents faster then perhaps the radiators will better able to keep up with steam production. My service person does not recommend down-firing the burner because of efficiency loss. Any advice would be greatly appreciated.

Abracadabra

more info?

model of boiler and burner?

Jason Quinn

Main vents

If you want to address the venting, start with your main vents. First make sure you have them- they are located at the end of the steam main and then verify that they are adequately sized. If you post pics and give measurements of the pipe diameter and length of the mains, I'm sure you'll get feedback here. Also, what pressure is your system running at? Most systems can operate with a cut in pressure of 1/2 psi and a cut out pressure of 2psi.

greengiant

make and model

Hi,

The boiler is a Weil McClain SGO, Model SGO-4. It is a four section boiler rated at 450 square feet of steam.

greengiant

main info and vents

I'll post pics soon if I still need to but my camera is out of batteries. In the mean time, two mains come from the boiler. One is 28 feet long, feeds 3 radiators that are relatively close to the main (the one furthest from it is on an 8 foot branch), and it ends back at the boiler with a Vent-Rite #31. The other main is not as simple. It also feeds 3 radiators however two of them are very far away down a branch off the main. The main extends 10 feet from the boiler. It then turns 180 degrees and goes straight back to the boiler, ending with another Vent-Rite #31. I believe that these vent are functional. If you hold a thread over the orifice you can see the air coming out. Branches from this main originate at the 180 degree turn. One branch travels 10 feet to a small radiator. The other branch travels about 25 feet to a T with 5 foot branches that feed 2 more radiators. There are no vents on any of the branch lines in the system. The only other vents are those on the radiators themselves, Vent-Rite #1's. I've got all the radiator vents open all the way. The cut in is set at 1/2 psi and the pressure guage on the boiler goes up to 2.5 before it cuts out. When the boiler cuts out, the pressure drops quickly and then the boiler refires. I hope this info is helpful. This system has 2" mains and 11/2 inch branch lines.

Jamie Hall

Bigger vents

might help a little, but honestly I doubt it.  Once the radiators are full of steam, they can condense it only just so fast -- and your boiler produces steam almost twice as fast as they can condense it -- so it has to cycle off and on.



Yes, downfiring does hurt efficiency, but most boiler and burner combinations can be downfired up to a point without too much of a hit; I'm not a burner man so I can't tell you how low you can go with that particular boiler.  Hopefully someone can come up with that information.

BobC

mains fast and radiators slow

In general you want to vent the mains fast and the radiators slowly. I don't know what the venting rates of those 31's is but it's probably somewhat slow. Venting radiators very fast usually causes more problems than it solves.



My boiler delivers way more steam than i have any use for and about all I could do was downfire it and vent the mains fast. the radiators are all vented slowly (#2 on the Hoffman 1A). How long does it take for the main vents to get hot from the time steam gets to the boiler riser (boiler should be cool when you start this test); then how long for the radiators to get hot after the vents are hot?



Can you turn that boiler pressure down so it stays below 1.5PSI?



Bob

Mark N

Oversized Boiler

How old is your boiler. Your boiler burns 1.2 gallons of oil an hour. A properly sized boiler like a Burnham MST288 burns .75 gallons an hour. Your burning an extra .45 gallons an hour every hour your boiler runs. That adds up to quite a bit of oil over the heating season, over the life of the boiler. I would look into down firing the boiler. So the efficiency drops a few points, burning an extra .45 gallons of oil an hour isn't efficient either. I assuming the boiler is somewhat new so replacing it isn't an option.

greengiant

New

Yes the boiler is new. I unfortunately made the mistake of sizing the new the same as the old boiler. Its a real shame

greengiant

pressure

Hi Bob,

I can turn the pressure down but then the boiler would cycle on and off even more rapidly. I was hoping I could keep the pressure lower in the system by rapidly venting radiators after their valves reopen to allow another shot of steam to enter them. It seems to me that quicker venting between condensing might keep the pressure down.

greengiant

timing

Hi,

I'll have to do the test and repost later about the timing.

greengiant

downfiring

Can I down fire the burner myself? Is that something that I can do? I have standard tools and am pretty handy but do not have any kind of electronics like my service guy uses.

jpf321

you really can't

unless you have a combustion analyzer .. if your service guy does have fancy electronics .. you are a few steps ahead of my guys .. use them but make sure they give you a printout of the readings straight from the machine. also make sure they do a smoke test with a proper smoke pull.



.. the key is that you have to maintain a certain minimum flue temp while downfiring and keeping your smoke and CO/O values in the right range. sure you can change the nozzle in just a few minutes, but you can't get the combustion readings that are necessary.