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Old copper radiant floor heating in concrete - try to use?

Couderay Member Posts: 314
Yes first and formost an air test is in order. When I installed my copper pipe in concrete put 100 psi in and capped it off. No you don't need that much pressure but a good 12 hour test@40 psi is a good place to start.


  • Tom Hopkins
    Tom Hopkins Member Posts: 554
    Worth saving old copper radiant heat in concrete?

    We had a new Buderus boiler and indirect DHW tank installed a few years ago. Very nice, highly recommend it. Anyway, at the time the installer talked us out of hooking up our copper radiant floor heating because he thought it would leak. He said portland cement is corrosive to copper and systems like this usually fail. If it didn't yet, it will soon and the fact that it hadn't been used for years makes it even more failure prone.

    I didn't want puddles of water in the basement and his explanation kinda made sense. But now we're getting back to figuring out how to heat the basement. I do like radiant floor heat and we'd probably be installing a system on top of this one. If there is a way to get the old one working again I think it would be a whole lot cheaper. Any thoughts?

    I think it's 1/2" type-L copper in the floor. At least, that's what comes out of the floor near the boiler. Would it be worthwhile to do a simple pressure test on the system? Hook up a gauge to one end and a hose to the other and see if it can hold, say, 40psi(???) for a week.

    What are some of the best practices if I put it back into service? I would have a pro do the hookup, but I'd like to be more informed this time around. I've heard some stuff about open/closed loop and people running stuff other than water through the pipes.

    Thanks in advance. This forum is great!
  • Joe is right

    Pressure test the radiant first . If it holds pressure I would connect it to the boiler like any other radiant zone with a mixing valve . But ...... if the boiler doesn't have one , install a low water cutoff and keep the boiler feed valve closed . That way you know when the radiant sprung a leak . And it will , eventually . How old is the radiant zone ? I work in Levittown and we still come across homes with the original 60 year old copper radiant still purrin' away .
  • Scott Larabee
    Scott Larabee Member Posts: 28


    I was going to ask about your thoughts on using a heat exchanger and making it its own closed system. Then I started to realize just how much that would cost! Probably not worth it, unless this home is to be unoccupied for long periods of time in the winter. My thought was that if it leaked, there would be only a small amount of water to leak out, and it wouldn't affect the system at all, but as I said, I think the cost would be prohibitive.

  • Actually , that depends....

    If you're frugal like me , you can just connect 2 pipes into an internal coil in the boiler and Viola ! Instant heat exchanger for a radiant ceiling in the bathroom .

    I guess the final say will depend on if he's going to finish the basement floor off . I'd go ahead and lay new radiant down if a new floor is gonna be the expensive variety . But if he decides to go with the old radiant , water damage from a leak might be minimal , if any at all . My own radiant leaked downward into the slab . Couldn't find the leak , couldn't fix it . Now I got a house wrapped in baseboard and I really miss the cozy floors .
  • Gordy
    Gordy Member Posts: 9,546

    Is the corrosive culprit to copper in a poured radiant slab.

    Mine is still functional and is 55 years old. Do a pressure test as been said. If it holds pressure hook it up. Concrete without radiant is a shame, especially if there is functioning tubing there that is not being used.

  • Scott Larabee
    Scott Larabee Member Posts: 28

    Thanks Ron,

    In his case, there is no coil in the boiler though, so he would neeed a heat exchanger. I guess the deciding factor would be what the damage potential is in determining what way to hook it up!

  • hot_rod
    hot_rod Member Posts: 22,147
    Yes it was the admix's

    in the concrete the COULD attack copper after time. If the area gets wet or damp, it would speed up the process.

    Both steel and copper would fail sooner if they ended up at the bottom of the pour in a potential wet area.

    Some of the backfill material used was found to attack copper also, like cinders or blast furnace slag, etc.

    Hard to predict if or when it may fail. Connect it as Ron mentioned and cross your fingers.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Jim R.
    Jim R. Member Posts: 58
    Thanks, lots of good info!

    I'll start with a pressure test. Should I do it with air or water or doesn't it matter? Air might be a little easier. Cap one end, hook the other to the air compressor at 40lbs and wait a week. Anything special or tips I should be aware of?

    If it's leaking, is there anything I can pump through to seal it? Kind of like a radiator stop-leak type of thing except for 1/2" pipe?

    I hate to abandon it or dig up portions of the floor to fix a few pinhole sized leaks (which my luck is probably the case).

    I'm not sure what we'll do with the floor. We have a guy who can pour an Ardex (thin layer of decorative concrete) floor for us, or we might use a mix of tile and carpet.

    With a potential leaky floor, maybe we'll do carpet squares or throw rugs. That's the wife's area though... :-)
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