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Recirculating solar gain in slab

KTim | Posted in General Questions on

We will be building a small 1100 sq ft bungalow, slab on grade, high insulation and air sealing. The slab will be the finished floor and we face south. In designing for some passive solar gain I am wondering about distributing the gain in the slab by recirculating through a radiant system without an additional heat source. i.e. small pump to move water in warm slab to cooler areas. 

Would that be effective or make sense to do? I am concerned about requiring a backup to the minisplit, don’t want to overheat, are putting in the pex anyways as this is DIY and easy to do at this point. 

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  1. Tom May | | #1

    Not sure of your design, but if your design includes a sun room, you can duct hot air using pvc pipe and small dc fans run off a small pv panel. Sounds like you want to install radiant in the hottest spot and distribute it. Another option is, if you can get your hands on some old cast iron radiators, use them....regular hot water baseboard will work also. There are other ways to collect hot water also.....

  2. Walter Ahlgrim | | #2

    It has been my experience that if you want to move much heat you need at least 15° of differential at each move. If the cool spot in your home are 30° cooler than the floor in your sun room you need to work on your insulation.

    I will admit the passive solar has an appeal but reality has not proven it to be the winning strategy. Once you start talking about pumps you are into active solar a real dead idea.

    The smart move is to build good wall and not big windows.


  3. Paul Wiedefeld | | #3

    A tiny electric baseboard/panel heater would provide backup much more effectively. I’d skip the in floor radiant entirely for a well insulated house of this size.

  4. Trevor Lambert | | #4

    If you're talking about moving heat within the same slab, what you're suggesting is going to have minimal effect. The two areas are already connected via a fairly heat conductive material 24/7, i.e. concrete. Water may conduct it a bit better, but when you factor in the small surface area, the small temperature difference and the fact it has to conduct through the PEX, I can't see it making a noticeable difference.

  5. KTim | | #5

    Thanks for the replies. It’s helpful!

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