Off Grid Home Forums Technical Discussion Radiant floor heat from fireplace

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    OK so the idea I have is placing a type of radiator behind my wood fired cookstove connected to PEX tubing radiant floor tubing. This would be a closed system that when the stove is in use it will heat the rad & circulate the glycol mix in the radiant floor tubing. I have considered a solar heater but our farm is in BC & so it would not work through the winter. Anyone seen something like this? Tips ideas?




    Water temp will be your biggest concern.

    Check the limits of the PEX you want to use then check the temp at the back of your stove. Will the glycol overheat the PEX?

    Do you have excess heat to transfer into the glycol?

    Think about how you will deal with all the various situations; most notably, stove working but no need for heating water. What would happen to the heat transfered into the glycol?

    Would you be better off with a fan?


    Hey thanks for replies (not sure what happened to the other one) I am still looking into this retrofit back boiler. I think it will work great. The PEX is ok until 200F & on a 1300 square ft house it should take quite a lot to overheat…. plus I am planning to have a temp sensitive check valve & quick disconnects to just “unplug” it when not needed. ANY tips etc. would be great!!!

    Thanks & I will keep you posted…..



    You might want to consider installing a heat exchanger. Circulate ethyl-glycol through the radiator in the fireplace, routed into an insulated hot water storage tank, from which you would pump a heated water/antifreeze mixture into your radiant floor’s PEX tubing as needed. A second thermostatically controlled cold-water valve/cooling-coil could be added to the storage tank to prevent overheating.


    I’m thinking of doing the same thing. Please keep us posted on your progress.


    Sucello where in BC is your farm located? I’m in the Prince George area


    In principle this is very similar to the outdoor wood fired boiler system for heating. If you leave the system open at the top you eliminate the risk of excessive heat causing the water to boil and creating steam pressure.This is when it enters the risk aspect. Depending on how effective your heat exchanger is and how much heat it can collect this scheme would work. In our wood boiler systems hot water PEX is used throughout for connecting

    Wood fired boilers are placed outdoors because it eliminates th emess of handling wood indoors and the insurance companies much prefer this. People with mortgages must provide insurance naming the mortgage holder as co beneficiary hence the desirability of the outdoor boilers. If insurance is not an issue go for it. Common sense should keep you out of trouble and guide you in assembling a safe durabel system. Eliminate pressuer build up install over heat warning near wood stove and do the layout to avoid air bubbles. If the stove is above the floor but you install the radiant heat radiators it might be a good thing to consider a circulation pump. thermo siphons only work on closed system but this introduces the risk of steam pressure build-up and you still have to contend with vapor locks and air bubbles.

    One caution.

    Unless you are only dealing with a very small home the indoor wood stove is not likely to deliver enough heat in BTU to properly drive the whole system. This is another reason why most systems use an outdoor boiler. The capacity of these are much higher and you do not have to worry about sustained burns with a forced draft. A normal indoor wood stove is designed to heat by radiant heat direct from the shell and letting air circulation carry heat to adjacent rooms. When you switch to hydronic heat you change the design parameters. Be sure your stove has adequate fire brick lining and solid welded shell construction and mind the flue for creosote buildup.

    Nick Rosen

    Just wondering how did the project go? Was it postponed or completed?

    I would always suggest to use a local expert, who knows best what works well in your state. It is especially important to know local codes. As well as, where to get the parts for the projects. Nowadays, internet prices are more competitive than at local supplies.

    For example, if you decide to get 1/2″ – 500 ft Pex Tubing with oxygen barrier online it can cost you around $140 –

    if you go to local supply it is around $220-260 for the same pex tubing with oxygen barrier.

    At the same time, even if you shop online prices may vary on brands. For example, 5″x12″ 50-plate heat exchanger for radiant floor heating you can get for around $1,200 for FlatPlate brand; or you can get Brazetek brand for $400×12-inch.-1-1/4-inch-mnpt-stainless-steel-copper-brazed-plate-heat-exchangers

    So, again I would recommend getting a local experienced contractor. Fixing mistakes is usually more costly than doing right way the first time.


    Sucello; the advice given by Peter is sound. Where in BC are you located. There are several outdoor boiler contractors in BC but not all are equally good. Several fly by night outfits have left customers out in the cold as opposed to high and dry. The restaurant here in Hixon is one such example. the quesnel dealer installed a system (cheap) but failed to correct several deficiencies. Eventually we got asked to fix it. but due to poor initial install it became a band aid fix not a great installation.

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