When it comes to installing radiant heat, the R-value of the subfloor is a key factor to consider. The R-value measures the ability of a two-dimensional barrier, such as a subfloor, to resist heat flow by conduction. You need a subfloor with an R-value high enough to ensure that your radiant heating system does not lose the heat that is released to the subfloor. The type of floor you choose to install on top of the radiant heat also matters. Generally, all floors can be used with radiant heat, although manufacturer recommendations should be consulted before installation.
Materials such as tile, stone and concrete are thermally conductive and work well with underfloor heating. Other materials, such as carpet, are less effective and can reduce heat flow. Installing a subfloor (or acoustic membrane) blocks the cold of the concrete slab, reflects heat directly to the ground and reduces vibration. If you are concerned about impact noise between people living in downstairs units, soundproofing the underfloor heating system with an acoustic membrane or a floor subfloor specially designed for this purpose can provide peace of mind.