Short cycling vs higher pressure??

laldog30cs

Very cold here in Boston this weekend, so let me start by saying I won't be undertaking any major changes in the next few weeks.

I cleaned out the pigtail, added a Hoffman main vent and knocked down the high pressure so it now cuts out around 4psi.

Unfortunately, the boiler cuts out (at 4 psi) well before the thermostat stops calling for heat. The boiler will run for about 5 minutes before the pressure rises to 4 and cuts out.

Eventually the house will warm up enough to satisfy the thermostat, but in the interest of economy and efficiency ($$)
is it better for the boiler to short cycle or run at a higher pressure??

On a positive note, I did insulate the basement pipes and my water consumption has declined considerably.
The effectiveness of the Hoffman Main vent (the big one) is definitely being reduced by piping restriction, but like I said, when the temperature outside is -5 degrees, it's really no time for messing around.

Thanks in advance for your advice.

Jamie Hall

Your pressure is still too high. Like... way too high. Step 1: dial it down to 1.5 psi, which is as low as you can go with a pressurestat.

Now. Having done that... it would appear that your main venting is still woefully inadequate. In the weather we are having just now -- unless the boiler is really wildly oversize -- you shouldn't see a pressure rise, never mind a cutout, until the boiler has been running at least 15 to 20 minutes, and until all the radiation is hot basically all the way across.

Can you tell us more about your main venting setup -- where they are, how much pipe is trying to go through them? And -- is this one pipe or two pipe steam? Can make a major difference in how to set up the vents!

Fred

4PSI is way too high. The higher the pressure, the slower steam moves. (sounds wierd put true) Set the Pressuretrol at .5PSI Cut-in and a Cut-out of 1.5 PSI. A single Hoffman #75 vent is not going to be enough for any average size steam main. You won't minimize your short cycles until you get adequate venting on the mains and each main needs those vents. I would let the boiler short cycle before I kept the pressure as high as you have it. That is just compounding the problem with getting steam through the system as quickly as possible.
Do you know if the boiler is significantly over sized for the attached radiation? Have you ever calculated the total EDR of the radiators and compared that to the Sq. Ft of steam output of the boiler? That number is stamped on the spec plate on the boiler. Being over sized is typically an issue with short cycling but probably not as significant as the main venting in terms of getting the steam to the radiators.

laldog30cs

It's a one pipe steam system.

I'm sure my venting is inadequate, but I honestly see very little of evidence that there ever was much.

Coming off the boiler, I have steam lines going in 6 different directions, each directly feeding a radiator in different parts of the house.

There appears to be a vent on one of these lines, but it was very small, more or less the size of a vent on the radiators.

I replaced this with the Hoffman #1, but like I said the piping leading up to the vent is very thin, thus restricting the effectiveness of the vent.

Further complicating things (and I would guess another major factor in the short-cycle scenario) is the fact that 2 radiators at one side of the house were removed in a remodel and never replaced. The radiator on the 2nd floor bedroom on the same side of the house has also been shut-off, basically cutting off about 1/3 of the house. Could this, in effect, make my boiler over-sized?

I'll get into more details as I collect more info. Clearly I've got some work to do.

Thanks for your help.

aircooled81

If you were air, in the system, where could you get out? Wise man has asked that more than once.
Do the airvents on your radiators still work? Do you want some help testing them?
I think if the boiler was sized correctly, you certainly have it oversized if you removed a large fraction of the radiant load.
Maybe a heating contractor can help you derate the boiler, to allow it to warm up slower, and run a bit longer. Maybe they can also aid in piping in adequate air vents.
Jmo

aircooled81

Ohh and to agree what the other wallies have said, you can not fix this issue with higher pressure. The short cycling is the lesser of two evils compared to the increase in pressure.

Jamie Hall

Taking those three radiators out has made your boiler at least half again oversized -- which isn't helping at all. It may be possible to down fire it, but that is a job for someone who really knows that sort of boiler.

With your piping -- which isn't all that unusual, by the way -- you really don't have mains as such. Thus you may have to really play with varying the vent sizes on the radiators to get the radiators even, but it can be done.

Fred

Maybe at least open the one radiator that is shut off. Is there any intent on putting the other two radiators back in? Are the supply lines still there? Do you still have the radiators stored somewhere?