Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

Hot tub radiant heat

<span style="font-size:12pt">Looking for opinions on circulating water from my hot tub through base board radiant heaters.</span>

<span style="font-size:12pt">The water in the hot tub is not chlorine or bromine; it is a hydrogen peroxide base so I don’t worry about corrosion in the system.</span>

<span style="font-size:12pt">I would like to inset a tee in line on the hot tub with a recirc pump and stat. send it through the house base boards and return it into the hot tub. The line would feed 4 base boards and defiantly less than 300 feet.</span>

<span style="font-size:12pt">Any suggestions or ideas would be grateful.</span>

<span style="font-size:12pt"> </span>

<span style="font-size:12pt">My questions are;</span>

<span style="font-size:12pt"> </span>

<span style="font-size:12pt">Will the water be hot enough at 102 deg?</span>

<span style="font-size:12pt">Would it be efficient enough for the work it will in tale?</span>


  • Zman
    Zman Member Posts: 7,115

    The water will eat the copper.

    The water will not be hot enough.

    You would be attempting to heat your house with electricity, not very efficient.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Bobo_momo
    Bobo_momo Member Posts: 3
    Hot Tub

    I understand the concern for the copper, but I don’t think that it would be an issue with the products used in the water.

    On the other hand what about running pex tubing under the floor instead of base boards?


    Is 102 deg warm enough to heat through a wood sub floor?


    Actual electricity is cheaper to heat with where I live, my house furnace is propane, it is $3.79 a gallon, and I need to get propane for $2.29 a gallon to equal the cost of electricity.

    This idea is to just supplement the furnace for one room in the house; it would not be primary heat. The hot tub is already hot and the heat is going to waste all day, so I would like to use it to my advantage.

  • SWEI
    SWEI Member Posts: 7,356
    edited October 2012
    oxygen and math

    We go to a lot of trouble to keep oxygen out of the water used in heating systems.  Peroxide can be thought of as supercharged oxygen.  Is there any ferrous material in your heating system?  If so, you can forget about directly using the hot tub water.  Peroxide will attack copper, brass, and solder more slowly, but it's still not a good idea.

    Using the residual heat might make sense - how many gallons does the tub hold?  The cheapest way to do this is to leave the tub inside and just let it cool down over time.  Hot bathtubs work nicely too.  If it's located outside, you'll need a heat exchanger designed for swimming pool use (typically made from titanium) plus two pumps and appropriate controls.

    102F would be your supply temp, so forget about baseboard -- you need as large a radiation surface as possible.  Return temp would need to be a max of 15F below that to avoid hotspots, so your average temp would be (at best) 94.5F which would work OK for a properly designed floor or ceiling system. Floor materials, building envelope, etc. will all need to be looked at carefully.

    Space heat using electric resistance occasionally pans out here in the US -- will help you make an informed decision.  Should you decide to do so, an electric boiler of similar capacity to your hot tub (which is probably undersized for the task) will probably cost far less than it would to integrate this properly.

    If you plan to derive the bulk of your heat from electricity, an air source heat pump is worth serious consideration.
  • Bobo_momo
    Bobo_momo Member Posts: 3

    Thank you for the wealth of information, and your time.
This discussion has been closed.