Radiant heat in an old house

gardiner

I live in a 1920's house with a nine year old boiler and steam radiators. When we redid our kitchen this year, our GC recommended that we should have radiant heat installed under the kitchen floor as an alternative to a regular radiator. After most of the installation had been accomplished, one of the technicians for the heating company told us we should repipe our boiler (for $2000+) or the radiant heat system might not work well. He said something about horizontal pipes and air accumulation. Well, this radiant heating system was quite expensive to begin with, so we made a fuss to our GC about thinking they should have seen this problem coming to begin with. NOW they're backpedaling and saying that the system should work o.k. without the repiping and that the technician had no business saying it wouldn't. Of course, it will be difficult for us to assess the efficiency of the new system because it is our first winter in this house. We need advice! Is it a mistake to install radiant heat for use with a boiler that might accumulate air? Is there an objective way to assess radiant heat efficiency? Any helpful comments on our situation?

gardiner

Please advise re. radiant heat in older home

I live in a 1920's house with a nine year old boiler and steam radiators. When we redid our kitchen this year, our GC recommended that we should have radiant heat installed under the kitchen floor as an alternative to a regular radiator. After most of the installation had been accomplished, one of the technicians for the heating company told us we should repipe our boiler (for $2000+) or the radiant heat system might not work well. He said something about horizontal pipes and air accumulation. Well, this radiant heating system was quite expensive to begin with, so we made a fuss to our GC because we felt that they should have seen this problem coming to begin with. NOW they're backpedaling and saying that the system should work o.k. without the repiping and that the technician had no business saying it wouldn't. Of course, it will be difficult for us to assess the efficiency of the new system because it is our first winter in this house. We need advice! Is it a mistake to install radiant heat for use with a boiler that might accumulate air? Is there an objective way to assess radiant heat efficiency? Any helpful comments on our situation?

Don Walsh

A few questions

Is your basic system steam or has the system been converted to hot water? You mentioned steam radiators being used and one of them being replaced by radiant. Have you any pictures of the boiler piping, and particularly the section of it that is being used for the radiant application?
A well designed system that is properly installed and controlled should be of no problem where air accumulation is concerned. If you could post a couple of pictures it would be of interest and if not, try to elaborate on how the system is currently piped near the boiler.

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gardiner

radiant heat

Thanks--the system is hot water with a gas boiler. When the new boiler was put in, they attached 1 1/2 " (OD) copper pipe to the boiler, and then adapted to the existing old piping (3" OD). The technician was concerned that where the adapters sat was especially problematic. The copper pipe goes upwards and the adapter is where the horizontal 3" pipe sits. He seemed to think that in the elbows, there would be air collection where the thread came in to the adapter. Here are two pictures though I couldnt quite capture the angle.

He first said he thought that without replacing those sections of horizontal pipe, the system might not work; then he said that we might have to be constantly going around the house and bleeding air from the key valves.

Steamhead

That's an old gravity hot-water system

You may just have a circulation problem here. The radiant zone has much more resistance in it than the old pipes and radiators did. These old systems had very low resistance so the water could be circulated without using a pump. So if the radiant is just hooked to the old gravity piping, water just won't go into it when the pump runs.

What I'd do is use a separate circulator pump for the radiant zone and maybe a mixing valve to limit the water temperature in that zone. This will make sure you get the proper circulation.

I'd also add an air separator to the supply line coming off the boiler if you don't already have one, then connect the expansion tank to the separator and install the circs next in line, pumping out toward the system instead of back toward the boiler. This will flush all the air back to the separator. This may have been what your tech was talking about. I can tell you it works for me!