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soft copper under wall-to-wall carpet

jcm55 Member Posts: 5
Bought a house this past June with in-floor radiant heat throughout. I suspect it was converted from baseboard at some point in the past. In any case, the system appears to send hi-temp water (170 F according to supply thermometer) through soft copper tubing under wall-to-wall carpeting which is everywhere in the house, except for the kitchen, which is linoleum.

#1 Radiant under carpet seems kind of strange to me. Is this common? Doesn't the carpet & padding insulate the piping from actually heating the room?

#2 Planning to do some remodeling, replacing flooring with hardwood. However, I'm thinking wood and hi-temp underfloor heating may not play well together. Any suggestions?


  • Robert_25
    Robert_25 Member Posts: 527
    Yes, the carpet and pad inhibit the heat transfer from the tubing - that is why your system is running at 170F. You will need to reduce the temperature if switching to hardwood flooring.

    What does the house have for a boiler? If it is a traditional cast iron boiler, some changes will likely be needed to the piping in order to run the reduced temperatures in the radiant system.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    edited November 2021
    They have carpet and padding that are lower r-values and radiant friendly. You may not even need 170° SWT. Maybe they have no way of mixing it down. Does that zone(s) run constantly on design day?
  • Ironman
    Ironman Member Posts: 7,373
    edited November 2021
    Are there heat transfer plates under the subfloor or is it some form of built up system on top of the sub floor?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • hot_rod
    hot_rod Member Posts: 22,118
    There could be a mixing device, linoleum does't do so well with that high of a temperature supply? About 140F it starts to squirm.
    How is the tube held to the floor? And the carpet over it?
    Send some pics if you can.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • jcm55
    jcm55 Member Posts: 5
    So first I should probably mention that the house was an estate sale, so I have zero info from the prior owner. He was a plumber who built the house in 1978 and passed away last year. A couple people in the trades have said things to me like "Oh, you bought Smith's [not real name] house? Good luck." Apparently he had a reputation for questionable work.

    I pulled up a corner of the carpet to see what was going on. Looks like the copper is embedded in thinset or something similar that's poured over the subfloor.

    Here are some photos the home inspector took when we bought the house back in June. System was not at full temp when these were taken. I think he turned the t-stats on just long enough to see a temp differential on the IR camera to confirm things were "working." The top of the 2nd photo is the same corner where I pulled the carpet back.

    Boiler is a Crown 195 Kbtu with a single circulator for the whole system:

    Pretty sure all the loops are home runs to the boiler room with no mixing. The horizontal supply and return that go behind the DHW tank run directly to the boiler.

    • The piping from the first two zone valves is capped off. Presumably these went to baseboards and were abandoned when the system was converted to radiant.
    • Third zone valve branches into five loops that cover the entire 1800 sqft second floor / main living area of the house.
    • Fourth zone valve is pegged open with no t-stat connected. It goes to a radiator in the master bath that is always on when any zone calls, and it gets insanely hot in there. There is a manual shutoff for this loop in the boiler room which I have closed now. Bathroom seems plenty warm without it, though we haven't gotten to coldest days yet.
    • Fifth zone valve branches into four loops that cover the 1200 sqft third floor. One of these loops doesn't seem to get any flow (based on feeling the supply / return). Don't know if it's airlocked, clogged or what. Third floor does not hold temp overnight, i.e. t-stat set for 68, and it's 65 up there by morning.
    • Sixth zone valve goes to a fan coil in the guest bed on the ground floor. Originally the blower was manually controlled by a switch on the unit, with the zone valve controlled by a separate wall thermostat. I added a 24v relay-in-a-box so the blower is now also controlled by the t-stat. The rest of the ground floor is garage, boiler room, and an unheated foyer.
    Supply and return temps: