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Ease of adding radiant floor loop to hot water system

MrZSpo Member Posts: 2
Hello all,

As I'm working through a kitchen renovation I'm thinking about removing a small radiator from the room and running pex with staple up aluminum heat transfer. 

The sq footage with the heated flooring would be around 125sq ft. I'm wondering if it is as easy as converting the current 1.5" copper pipes leading to and from that radiator into the 1/2 pex line and calling it a day, or if such a dramatic step down in size will cause issues.

I've read that because this location of floor heating has to go through about an inch and a half of flooring the higher temps of my system wouldn't be an issue, as I've read with radiant heating closer to the surface. 

Any insight would be appreciated.


  • Jamie Hall
    Jamie Hall Member Posts: 23,433
    How small is small? The first thing to do is to decide whether the floor -- at a comfortable floor temperature -- can provide the heat you need in the kitchen. A sort of generally accepted maximum output for radiant floors is around 30 BTUh per square foot, which would be around 3600 BTUh for your floor area. This is less than a 1500 watt electric space heater. Is it enough for the space?

    Then the next consideration is that radiant floors operate best with continuous circulation at relatively low temperatures. While they can operate with higher temperature water turning on and off, it's not the best solution. Ideally then, you would want to run the floor with its own little circulator and a mixing valve, taking some of the return water from the floor and mixing it with just enough hot water from your regular system to maintain the floor temperature. Not that your idea won't work, but it won't maintain the floor at anything like a constant temperature, and you will difficulty controlling it.

    And the last consideration I will mention is insulation. With that much floor above the plates, you will need considerable insulation below them to avoid losing your heat downwards -- which you don't want.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • MrZSpo
    MrZSpo Member Posts: 2
    @Jamie Hall it's about 2 ft tall maybe 2.5ft wide, the reason I'm thinking about this option is specifically because that radiator seemingly provides no heat (it gets hot but not nearly enough to matter in the room)

    If the heated floors without their own loop heats even as well as that little guy then it's worth it to me just to not have it taking up space. 

    I'm guessing running a separate loop with it's own pump and mix valve and all might increase the job past my diy level.