Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.

If you've found help here, check back in to let us know how everything worked out.
It's a great way to thank those who helped you.
Need to contact us? Visit

Too much condensate in supply line ... and plumbing issue?

jefffjefff Member Posts: 4
I've got a historically under-heating radiator in a converted porch room. It is quite obvious to me that this radiator was added significantly after the house was built (1929).

The radiator in question is supplied off one of two main branches, which then exits the basement through the foundation wall into the garage and has about 25 feet of minimally insulated horizontal-ish pipe until it comes out into the converted porch space.

Additionally, the radiator is connected to the supply and return at the top and bottom of the same side with an inlet valve and no trap whatsoever. This seems to me like it would "short circuit" the majority of the radiator.

When I bought the house 1.5 years ago, the radiator had an air vent on the far end. After some research about vapor-vacuum systems, I replaced this with a pipe plug, but this doesn't seem to have changed anything.

While investigating this, I've run the system with the air vent off. Result: lots of gurgling and minimal steam until quite some time into the heating cycle.

I've also run it with the radiator disconnected to see what was happening with the supply line. Result was minimal steam bubbling up through quite a bit of condensate in the supply line. Video of this experimenting :

After 15 minutes of doing this, the supply eventually yielded a strong steady supply of steam (at which point I had the valve back on) but still didn't heat the radiator appreciably.

Quick summary of the rest of the system:
The rest of the radiators are very uniform in style, thin tube with graduated inlet regulating valves at the top, and hoffman thermostatic traps at the bottom of the opposite end. The boiler is a newer Weil Mclain. The steam mains drop into wet returns, and there is a parallel dry return dropping into the wet return at the same point. There is a crossover thermostatic trap at the end of the steam main into the dry return (similar to what is on each radiator). Near the boiler end, there is a hoffman differential loop between the steam main and dry return, with the appropriate overflow into the wet return and a Hoffman #15 vacuum vent at the highest end of the dry return.

What can I do to increase the heat output of this radiator?

My semi-informed guesswork:
1) replumb the return side to the opposite end of the radiator to force the entire radiator to fill.
2) correct the slope and/or insulate the horizontal run out to this radiator (which way?)
3) somehow add a trap or a drip to the supply side to remove the condensate and deliver steam faster

Thanks in advance!


  • Jamie HallJamie Hall Member Posts: 12,719
    The essential thing to do is to recognise that what is happening is normal -- steam going into that supply pipe has to heat the whole thing -- generating a lot of condensate -- before it even has a chance to get to the radiator. I feel sorry for it...

    That said, it is clear that two things need to happen: the amount of condensate in the line needs to be reduced, and the way to do that is insulation -- heavy insulation, if it is in a crawl space. Two inches will be none too much. Second, the pipe mus be pitched to drain, and bizarre as it may seem in this particular instance I would see if it was possible to pitch it to drain at the radiator end, and put a standard radiator trap at the low point to go into the return from the radiator -- before it got to the radiator. That trap must be plumbed to drain the condensate (a normal cross over trap would come off the top -- this must come off the side or, preferably, the bottom). If I couldn't arrange it that way, I would enlarge that pipe and pitch it as though it were a one pipe counterflow radiator system.

    I doubt very much that the vent on the radiator is helping any.

    The presence of a differential loop tells me that this is a Hoffman Equipped system. There is one really important thing about them: they must not run at any pressure above 12 ounces. If you do not have a vapourstat to limit that, you need one. The Differential Loop will trip at any pressure above that (some trip at slightly less), and pressurize the dry returns -- at which point heating will stop until the boiler shuts off and the pressure has a chance to drop again. This is a waste of fuel (and money...). That's the way it's supposed to work; don't defeat it!
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • AbracadabraAbracadabra Member Posts: 1,948
    The radiator setup is seriously knuckleheaded. Got pictures of other radiators in the house?
  • jefffjefff Member Posts: 4
    Jamie - thanks a ton for the insight. I will uncover the horizontal run and see which way I might be able to pitch the pipe. Its in a garage wall covered by 1/2" wood siding, so semi-easy access.

    The vaporstat should just swap in for the pressuretrol, correct? No other modifications needed?

    Abracadabra - The other radiators in the house are fairly standard, see the couple pictures below. Any suggestions on replumbing that radiator? My thoughts are to bring the return under the radiator to the far side and add a steam trap at that point.

  • AbracadabraAbracadabra Member Posts: 1,948
    jefff said:

    Abracadabra - The other radiators in the house are fairly standard, see the couple pictures below. Any suggestions on replumbing that radiator? My thoughts are to bring the return under the radiator to the far side and add a steam trap at that point.

    That's what I'd do. Assuming the return pipe on the knuckleheaded radiator connects properly to a return.

Sign In or Register to comment.


It looks like you're new here. If you want to get involved, click one of these buttons!