insulation for radiant floor

Tyler Kingery

I have a very basic question on when to use insulation on a radiant floor system. Should you always insulate a radiant floor or are there exceptions?

Mike T., Swampeast MO

If you're talking about embedded tube in slab-on-grade you MUST insulate the EDGES of the slab. It has become "customary" to insulate the underside as well. If you don't insulate the edges you provide a CONDUCTION route to the great outdoors where your heat is robbed by CONVECTION. Under the slab gets really strange as insulation only SLOWS heat transfer and there is no convection under the ground yet the ground is both a very good source for and a very good reservoir for heat....

If you're talking about bare tube systems installed under a floor, yes you MUST insulate--as perfectly as you can accomplish. "Insulation" here HEAVILY involves "air sealing" so that you keep the convection where you WANT the convection...

If you're talking about tube-in-plates-attached-to-the-floor YES you want to insulate DIRECTLY against the plates. An exception to this "rule" is if this is a space with extremely low exposure and, by design, you want to "loose" a bit of heat via RADIATION.

If you're talking about a system that places the tube in a heavily CONDUCTIVE surface (like Warmboard or the structural Ruheau (sp) floor surfaces) you MUST ENSURE that the insulation value BELOW such is significantly HIGHER than that above.