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Community and Q&A

Running PEX in-floor in addition to baseboard

George LaLonde | Posted in Mechanicals on

I’m building a new wood frame home with hot water baseboard heating in climate zone 6. The bathroom will have tile floors and I was thinking of using some electric resistance heat under the tile along with a baseboard hot water radiator in the bathroom. These electric systems are not inexpensive to install or operate so I am now considering simply running loops of Pex (the supply line to the bathroom radiator) between the joists to keep the tiles warm before the water in the line gets to the baseboard radiator.
The goal is to keep the chill out of the tile while still allowing the radiator to actually heat the room.
The PEX could be stapled directly to the subfloor or installed with typical aluminum reflectors as done w in-floor heating.
The bathroom is on a dedicated zone for that space only.
Any problems with this?

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  1. GBA Editor
    Martin Holladay | | #1

    Q. "Any problems with this?"

    A. Yes. Hydronic baseboards usually require higher water temperatures than the temperatures recommended for in-floor radiant heating systems. There are solutions to this problem, but it's important to make sure that you aren't using 180 degree water to heat your subfloor.

  2. George LaLonde | | #2

    That was my concern Martin. Can this be addressed by incorporating some sort of mixing valve or other means of cooling the water in only this one zone? Would the water be cooled enough if run thru the baseboard radiator 1st ?
    Given the need for so many systems (H/W heat, mini-split A/C, HRV etc) in these new, tight houses I would like to simplify whenever possible.

  3. GBA Editor
    Martin Holladay | | #3

    It sounds like you may need to hire a qualified mechanical engineer or experienced HVAC contractor to design your hydronic system.

    1. You need to have performed an accurate room-by-room heating load calculation.

    2. You need to know the water temperature that you intend to run through your hydronic baseboard. If you are designing your system for 120 degree water, you will need more linear feet of baseboard than if you are designing your system for 180 degree water.

    3. You don't necessarily need both infloor hydronic tubing and hydronic baseboard in your bathroom -- just one of these methods of heat distribution may be all you need. But there is no way of knowing until you perform a heat loss calculation and begin designing your system.

    4. If you decide to deliver different water temperatures to different hydronic loads, you may need to install a thermostatic mixing valve -- for example, one like this:

    But there are lots of ways to control a hydronic system -- so if all of this is new to you, it's time to talk to a qualified mechanical engineer.

  4. George LaLonde | | #4

    Thanks again Martin. I find myself in the un-enviable position of building in a small resort community at a time when this area is in the midst of a building boom and all the trades and suppliers are basically too busy to give adequate thought to small, out of the norm, projects. I expect this problem is ramping up across the entire country as we come out of the recession having lost so many skilled tradesmen.

  5. Aj Builder, Upstate NY Zone 6a | | #5

    Richard McGrath will most likely help you out George. search his name, he has posted his phone number and email too on some threads.

    Stick with above floor installs as I have done the underfloor plates... I would not do just a bathroom with underfloor plates. I have installs of electric matt and if only used for the morning get out of bed time, they are the best and they use very little energy since they are on for a short time.

    Schluter now makes a floor matt just for floor heat, Home Depot carries it even in my store. Take a look at it,

    The idea for many is to have the floor heat on when barefoot, and getting up... used just for that period, go electric, you'll love it. You'll have better control, much better control.

  6. Richard McGrath | | #6

    George ,

    Feel free to contact me at 732-581-3833 or by e mail at [email protected] .

    This is quite painless and easily done . All I require from you is some basic information and how much baseboard is in the room at present along with performing a single room heat loss calc . we'll get you set right up .

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