Oversized or overfired w/ a lousy pressuretrol?

Mitch Henderson

Summary: I have a new Wiel Mcclean SGO5 boiler feeding a single pipe radiator system on a 2500 sq. ft side of a side by side here in Providence (built in 1902 to 2.0 psi specs!). After running for 36-38 minutes, the steam pressure starts rising and I get 7 short cycles of 4+ minutes each (3 minutes burner on, 1 minute off). Between time 30 and time 60, the temperature in the house rises 1 degree F every seven minutes whether the temperature outside was 25, 40, or 43 degrees while this cycling is going on..

The Honeywell 404A pressurtrol is NOW set to about 1.9 and .9 lbs plus or minus who knows how much (have tried two pressure gages so far that don’t seem to agree exactly). That’s about as low as I can get the pressure set before the screw comes out of the presuretrol. I set the white differential wheel DOWN to 1 lb. which is as low as it will go. (White Fuel likes a setting of 2psi on the wheel)

I have all new vents with the first floor ones open fully and the second/ third floor at about ½ since heat rises. The vents seem to be working fine…especially after installing a low pressure quick start vent in the living room BIG long radiator where the termostat is. Burner firing rate is 1.35 gal/min.

Questions:

1. Based on your literature, I conclude the boiler is oversized or properly sized but overfired. (I know Bruce Willard of White Fuel was conservative in sizing the boiler) (Thermostat is ok – pressuresol is controling burner for sure.. Wet steam doesn’t seem to be a problem tho when the pressure was up at 5 psi once, several vents sputurred a lot and the vents slammed shut. At 2 psi, there’s no problem.). Bruce Willard at White Fuel who sold me the boiler isn’t sure if lowering the firing rate is going to solve the problem given that I’ve lowered the pressuretrol settings from 3psi/1psi . Given the cycle times and the fact that it only takes 3 minutes for the steam to go up to 2-2.5 psi during a cycle, I’m not sure that lowering the firing rate to say 1.25 or 1.2 will “be enough” – the cycles may just be a little longer and I’ll get say 5 instead of 7 cycles? What do you think?

2. I want to install a L408B Honeywell Vaporstat but White Fuel and Wiel Mcclain whom Bruce talked to aren’t sure if one makes sense per your book and whether the warranty becomes void if a pressuresol isn’t used. Seems to me if I installed one I will get more accurate settings iand could home in on your 1.5 and .5 psi cutout/in but that might make for even more cycling. What do you think? (I've even thought maybe we ought to put a time delay on the burner so it doesn't come on for 5-10 minutes after being shutdown by pressure controls).

As you can probably tell, I’m an engineer – exNavy nuclear submariner – who knows just enough to be dangerous. ( Like where's the throttle on this baby????)I’m driving White Fuel nuts with questions but we need a minute of some real experts to set us straight. We would really appreciate answer(s) to this problem set if you have time.

Steamhead

Might be oversized

You need to add up all the radiation on the system. For radiator sizing info, get a copy of Dan's "E.D.R." which is a fascinating compilation of old radiator catalogs. You can order it on the Books and More page of this site.

Once we know how many square feet of radiation you have, we can compare it to the boiler's rating. We may end up down-firing the boiler to match the radiation.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Mitch Henderson

Radiator calculations

Took measurements with Bruce the contractor; will send to you when I get them from him. Thanks

Mitch Henderson

Radiator calculations

Contractor assures me unit isn't oversized. Even if it is a little, it's installed.
The question is: is it normal to run for 30 minutes and then have pressure cycle by pressuretrol 6-7 times on 4 minute cycles? Can cutting back on firing rate help? Should I purchase a vaporstat?

oil-2-4-6-gas

.

you can drop a section then fire it at the correct rate for the 4 section