head scratcher

mikemc · January 2016

new customer, has had 3 different contractors since being there3 yrs now.
10 yr old burnham boiler, residential, piped in properly. however, the 2nd flr was cut out and is being heated by forced air now. all pipes must have been capped/plugged, new flooring covers all signs now. 86 yr old house. 2-pipe steam, 1 main supply header (goes into rest of bsmt w/ finished ceilings) and 3 return mains. each return had a steam vent close to boiler. each line had a different brand though, and one was a vaccum breaker. tried replacing it and another I suspected wasn't working properly with standard main steam vent, I realized that one of them had to be going to 2nd flr and still never got steam back to boiler. after starting system from cold, it runs for 25-40 minutes and after pressuretroll hits 1.5 psi burners shut down. diff at .5 (was set at 6 psi when I arrived) but after this, (and radiators are getting hot) the boiler then starts short cycling. 1.5 min off and 2-3 min on. then sometimes shuts off for hours the customer says with no heat at all.... boiler is sized properly for the radiation on 1st floor but who know about piping with 2nd flr off now. no apparent signs of too much condensate coming back and has an auto feeder. gggrrrrrrr have I left enough info for you???

Abracadabra · January 2016

You sure the boiler isn't oversized now that the 2nd floor is not connected to boiler? Sounds like it from what you are saying.

Steamhead · January 2016

Sounds like a butchered Vapor system.

These are usually piped with one set of pipes feeding radiators on all floors. What you see in the boiler room is probably one or more "dry returns" which carry the air and condensate from radiators. If this is a typical Vapor system with traps on the radiators, these dry returns should never have steam in them at all.

Have you been able to find the return from the end of the steam main(s)?

mikemc · January 2016

your gonna have to excuse me if I don't sound as smart as most the guys on here... you mean the end of the supply? the farthest point from the boiler? if so, its in a nasty looking crawl space that I was planning on trying wed.
yes, dry returns, sorry forgot to mention that, after the long run time from cold boiler the returns get blazing hot after a while. just condensate wouldn't do that right?

Steamhead · January 2016

Right. This means you have bad radiator traps somewhere.

I bet you find either a main vent or a crossover trap in that crawlspace.

mikemc · January 2016

no, I measured the radiators and got sq ft from weil mclain book and says I need 114,000. boiler is 140,000 in @ 81%

mikemc · January 2016

and, I thought I would be getting erratic condensate levels if it was oversized too

Steamhead · January 2016

mikemc said:
no, I measured the radiators and got sq ft from weil mclain book and says I need 114,000. boiler is 140,000 in @ 81%

Something doesn't add up here. Are you saying the radiators are rated 114,000 BTUH (which equals 475 square feet) and the boiler's Input rating is 140,000 BTUH?

mikemc · January 2016

yes, I have radiators adding up to 475 sq ft at @ 240 btu's per sq ft. giving me 114,000 btu's needed. there is a 140,000 btu boiler in there.
I found no main vents in that crawlspace but found one in the dirt from some time ago. I assume someone cut it out (accidentally maybe) when they cut the piping to 2nd floor back when they put a forced air system up there. looks like that was in 08. I did have 2 thermostatic traps in crawl for 2 low profile baseboard radiators in living rm but no vents other than one in the dirt I assume came from the piping in the crawl at some point.

ChrisJ · January 2016

114,000 btu/h needed with zero loss for piping and that boiler's DOE output is what, 114,000 btu/h at best?

Even by my standards that's a small boiler for the connected load.

Jamie Hall · January 2016

Somewhere... back in there... there is, or was, at least one crossover trap. It's going to be a nuisance, because who knows what was cut out, but... you need to find the end of each steam main. There, or very close to there, you either need a crossover trap or, since it has been mangled, a several good big vents might be easier to manage.

Make sure your pressure is correct; it sounds as though it is, and the cycling you mention is characteristic of a slightly oversized system -- although if I read your numbers correctly, this one isn't --140,000 BTU input at 81% is 113,000 BTU out, which makes no allowance for pickup or other losses in the system.

Then you also need to find out where you have a problem which makes the returns hot. It probably is one or more bad traps, and the best way to find them is to run the system and see if you can find out where the returns get hot first, or keep dashing about and find out which radiator(s) are passing steam.

While you are at it, trace every single pipe. It is possible that someone did something really strange while they were taking the steam out of the third floor...

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