On-Slab Radiant Floor Heating Feasiblity

KerryLDecember 17, 2012

Hello all!

I am renovating a room in my house and am considering installing hydronic radiant heat in the floor, but I have some questions and concerns to address before diving in. The room is on the first floor and is on a slab. It was built in 1960 and there is no insulation around the outside of the slab nor on either side of the block wall (and presumably nothing underneath, either).

My thought is that the best plan is to install a plywood subfloor (probably on top of 6 mil polyethylene) and run the tubing through grooves cut in the subfloor (there are some commercial products available, or I may cut the grooves myself). The finish flooring would be on top of the plywood (haven't decided on flooring yet, but we like the look and feel of hardwood).

Radiant heat installed IN the slab seems to be a popular approach, but since this is an existing slab, is radiant heat still a good option? Usually you have the benefit of the thermal mass of the slab - do I want to count on that, or add rigid insulation below the subfloor (this is less attractive, becuase this room already has a ~7' ceiling, so every inch counts)?

Also, we have a boiler (the rest of the house is hydronic baseboard heat), and I believe I would need a 4-way mixing valve to reduce the temperature of the water circuling in the floor and increase the temperature of the water heading back to the boiler. I think there is an efficiency hit here, since we'll still be heating the water to 180 deg, but I'm not sure that it's a deal breaker (interested to hear opionions on this, too).

My fallback is traditional baseboard radiators (which is the way this room has been heated for the last 50 years).

Any thoughts? Should I just use the baseboard radiators, or is this really a viable approach?



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What you're proposing is certainly feasible using your existing boiler and some sort of 3 or 4 way mixing valve or assembly.

Your floor would have to be isolated from the existing slab and you would not benefit from a thermal mass. However, you may have faster reaction times. Keep in mind that pipe spacing is related to water temperature so make sure of your design before starting and ordering materials.

Do consult with a radiant in-floor specialist that understands hydronic boilers as well - you don't want surprises!


    Bookmark   December 17, 2012 at 9:21PM
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just wondering why you are considering the much more expensive hydronic over electric radiant heat?? How big is the room you are heating?

    Bookmark   December 22, 2012 at 4:46PM
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