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Replacing Toe Kick heater with radiant loop - how to size

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MarkBK
MarkBK Member Posts: 6
in Radiant Heating
I want to replace a toe kick heater with a radiant loop in the ceiling or wall and want to know how many feet of tubing this will require. The toe kick heater is the sole source of heat in an ADU (Auxilary Dwelling Unit) in Seattle Washington. The toe kick heater is a failure--I assume that is because the rest of the radiant system is using pex loops and so the glycol temp is only 90-100 degrees. The toe kick must require a higher temp to be useful. I believe the previous owner was planning to put loops onto the slab, but I don't want to do that. I'll put down cork flooring on the uninsulated former garage slab. There is a manifold in the ADU with places to have three loops (one is feeding the toe kick).

Do I need a full heat loss calc or can I just use some rule of thumb to put in sufficient footage of PEX?

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  • Jamie Hall
    Jamie Hall Member Posts: 23,336
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    No good rules of thumb. However, find the Slant/Fin heat loss calculator -- it's simple to use and quick -- and start with that.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Gordy
    Gordy Member Posts: 9,546
    edited January 2019
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    Do a heat load calc for the room to see the load. Then you can decide how many SF of radiant panel will be needed at the water temp you are running now. Then you can see how many SF of available ceiling, and or wall space will be needed.

    What is the heat source for the system?

    Another option provided the kick space heater was sized properly to the load for it’s rated water temp is use a mixing valve for the radiant to maintain the present supply temp, and send the rated supply water temp for the kick space heater. This would save doing demo, and install of a radiant ceiling, or wall. Unless the demo is part of a remodel anyway.
  • MarkBK
    MarkBK Member Posts: 6
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    The heat source is a Purefire gas boiler. I don't have any reason to think the kick space heater was sized properly since no provision was made to sent it water warm enough to make it work. I am just a handyman/homeowner and don't want to fool with or alter the house radiant system if possible. I just want to add enough tubing or other type of emitter to the ADU so that it is warm. Basically I have a 1 inch pex circuit out there on its own Grundfos pump controlled by a thermostat to work with. There is a three tube manifold out there to step down to 1/2 inch PEX. So I can add a couple of loops--just need to calc how many feet.

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