Intermittent Heat on Several Radiators

JackVinner

I'm the owner of a 12 unit building (2 floors 6 units with 3 radiators per unit) that is heated by a 1 pipe counter flow steam system. Over the last few years, I've replaced the boiler, corrected some incorrect up and down pipes and replaced some buried, but leaky, steam pipes. The system is much better than it used to be but there are still several things that keep me scratching my head and wonder if the collective brains here can help me out. Steam is controlled by a thermostat in the hallway and a vaporstat (Honeywell) diff set to 2 oz and the main set to 11oz. There is also a (honeywell) pressuretrol set to 5PSI Main. There are two main vents (Hoffman 75).

Main Problem - For the last few months I have had a vacant apartment on the first floor close to the boiler room that was heating nicely, i.e., all three radiators were heating. During the recent cold snap all three radiators suddenly went cold. All are sloped correctly and were giving off heat nicely prior. Also there doesn't appear to be a heating capacity issue with the building as the boiler is likely oversized. (I had to have the boiler down fired as it was short cycling a couple of years ago after the install.) No other units complained about heat. In my efforts to restore heat to the vacant unit, I took off the hoffman 40 vents and felt air moving out of the radiator like a person breathing lightly. I did notice some water in the hoffman 40 vent but that could have just been residue condensation. Thinking that this was a venting issue, I replaced the main Hoffman 75 vents with new Hoffman 75's. I actually have 2 big mouth vents and while I can fit it on one of the mains, a joist prohibits me from installing it on another and I hesitate to vent the 2 mains at substantially different rates since I really haven't had much of a balancing issue. While the vents were off the radiators I was able to get heat into the first 3 or 4 sections of the radiator in the living room but even with the vents off, I couldn't get heat in the bathroom or bedroom (radiators closest to the boiler returns) radiators. After an hour or so I replaced the vents on the radiators. Then a day latter the radiators were all filled with steam. The other issue I noted is when I replaced the first main vent, the vent heated very hot while the second main, close to the aforementioned apartment, wasn't as hot and didn't appear to be venting that well. Certainly there was no billowing steam coming out of either but the second seemed less than the first. Of course this is the vent that I can't get the big mouth on.


Other questions: 1) Can you replace Schedule 40 pipe with Schedule 80 pipe? 80 is thicker but I wonder if this somehow impacts the dynamics of a counter flow system. 2) Many of my tenants choose to close the service valves of their radiators. Would turning these on during a cold snap substantively impact the balance of the system. Is there too little pressure in this system? I've heard that less pressure is better but maybe I've over compensated. Thanks for your help.

nicholas bonham-carter

Your pressure is nice and low, but allowing the tenants to close the valves on the inlet is very unwise. First find out why they wish to do this, and Then take the handles off, and tighten up the packing nuts, so they will not easily be able to close the valves even with pliers.
This could be a control problem, where the thermostat is in a cold area, and by the time it has been satisfied, the other areas are sweltering. If you are using night setback, then this forces the system to play catch-up and costs you fuel, and exaggerates any imbalance in the steam delivery. You can use a lower constant temperature instead of high and low, for greater comfort and economy.—NBC

Fred

It sounds like there is water pooled in the run outs. Are they properly pitched? I'm also wondering if you have the boiler down fired while some of the tenants had radiators shut off and with the recent cold snap, they all opened their radiator valves and the down fired boiler couldn't produce enough steam to feed all of the radiators.

JackVinner

Thanks for the comments. Answering some of the questions 1) there is no setback on the thermostat. True the Thermostat sits in the hallway that will be colder than the units but that is locked in at 70 degrees. Even when I turned it up to 80, there was no heat in that one unit. But magically heated a day or two later with the thermostat set at the set 70 degrees. Understand that this very well would cause people to turn off the radiator service value. Good suggestion regarding essentially taking off the handles. But still curious about the root cause of the intermittent heat issue in this one unit?

Regarding the hypothesis of pooled water in the run outs, I haven't received complaints about water hammering. Also under this apartment I recently replaced a leaky pipe with Schedule 80 taking care to preserve the proper slope for counterflow and insulating since it was basically in soil. But again I would think it would either not work (pooled water) or work or at least give me a hammering noise. Shouldn't be intermittent. Should it?

Since it was so cold last week it is very possible that everyone opened their previously shut radiators and the down fired boiler couldn't produce enough steam. Guess I'll have to monitor this a bit more and ensure that all the service valves are open.

Thanks.

Jamie Hall

The breathing in and out which you mention strongly suggests pooled water somewhere. It won't necessarily hammer -- although I admit that usually it would. But a combination of really cold (with a possibly undersized boiler now) and that pipe which you describe as "basically in soil" makes me wonder a little if perhaps there simply wasn't enough steam to heat that pipe enough to get steam on through. We sometimes forget that the pipe doesn't just allow steam to go from one end to the other, like air or water, but that in order to get from one end to the other the steam has to heat the pipe enough -- and keep it that way -- to avoid condensing as it goes along.

And soil is a much better conductor of heat than free air would be!