One pipe radiator on a two pipe system

dvnyc

My home is heated by a two pipe steam, fed by a Weil Mclain steam boiler with the radiators that exit to a dry return through Hoffman 17c steam traps with one exception. There is one radiator that is setup with its own vent, and only a single pipe to the main. In the basement, I can see the capped original return pipe for that radiator. My guess is it was done when the kitchen was remodeled by the previous owner. Other than this one radiator hissing on startup, the heating system seems to work fine. How big of the deal is this? is it worth the effort reconfiguring this one pipe radiator back to a two pipe configuration?

Jamie Hall

As long as it's a conventional two pipe system -- main vents at the ends of the mains and on the dry returns -- there's no harm to it at all. Leave it be.

johnshanahan

Our building of nine condominiums in an old 1896 Denver square is heated by two pipe steam. It has an old Dunham Return System (originally vapor) that was converted from coal to gas. Every radiator is two pipe with steam traps save one. There is one unit where the developer that did the condo conversion installed a radiator just like above: one supply (and return) pipe on the bottom of the radiator, pitch toward the valve, with an air vent half-way up the opposite side. It works without water hammer. We had debated whether to repipe it and decided against it due to cost. I now feel good about the decision.

ethicalpaul

I can't think of a reason why a "mixed" system like this would have any trouble…if steam with a little pressure is available at the supply pipe going to this radiator, it's fine.

But my question is: why is the vent hissing? Do you have main vents operating? Is the boiler oversized? Are the pressure controls set too high?

jumper

I'm surprised this works. Condensate from one pipe goes into supply?

Jamie Hall

https://forum.heatinghelp.com/discussion/comment/1801452#Comment_1801452

Yes — just like condensate from the pipe itself. If it's just one radiator, unless it's huge, it's no big deal.

redxiii5665

https://forum.heatinghelp.com/discussion/comment/1801165#Comment_1801165

Due to the one pipe, it has to release air to fill with steam making a light breathy hiss and take in air to release condensate, the hiss should be stopping once the steam pressure rises enough in the radiator, if not then I would replace the vent valve if it has some age to it, internal seals might be worn

ethicalpaul

OK. Just for comparison, none of my vents can normally be heard (but the air escaping can be detected with a wet finger or careful close listening).

When people say "hissing" I think "hissing", not "light breathy hiss" so if you have the latter, all good.

There is nothing about venting in a 1 pipe radiator that allows the release of condensate. They are built so that the water will flow out regardless of pressure.

The air escape should stop not when steam pressure rises enough, but rather when steam gets to the vent and closes it. Or if your system is really properly sized and balanced, the call for heat will end before the radiator is completely full of steam.