Warmboard vs Radiant in concrete

orange_cat

Have an odd situation where we have installed but have not yet connected radiant tubing - slab on grade foundation, with insulation over the base, then tubing, then 4 inches of cement. Solid hardwood (rift cut 4-inch boards) is intended to go on top. It is a new extension of the house.

We are now considering installing warmboard over that cement area and connecting tubing over warmboard instead of to tubing in cement (has to do with finished height and connection between rooms). Have warmboard elsewhere.

The area is small, so the cost of installing warmboard is not large. Assumption is that there will be less of a heat loss (this is a heating-dominating climate, zone 5) (and the main reason is the height discrepancy between extension and existing flooring).

DCContrarian

The heat loss is really going to be driven by how much insulation you put under the concrete. Concrete is highly conductive, there's not going to be much difference between putting the tubes at the top or the bottom unless you add more insulation between the warmboard and the concrete.

One of the selling points of Warmboard is that it's highly responsive, because it has a low heat capacity. That advantage is lost if it's in direct contact with the concrete though.