Although floor coverings can not change the efficiency of your heating system, they can greatly affect the ability of the floor to heat your home.
    Concrete, tile, brick, and vinyl are very good choices for floors with radiant heat, but most people will choose carpeting. Carpet and pad by their nature are thermal insulators.
    Carpet generally has less effect than the pad does on the ability of the floor to heat the room. Generally, the R-value of synthetic carpet can be determined by it's thickness. They range from R-1.0 for 1/4" carpet to R- 2.0 for 1" carpet. If you plan on using wool carpet you need to let your designer know first. 

    Although there are many types of carpet cushion, we only recommend the rubber types for a radiant floor. The rubber cushions come in two types, slab and ribbed or waffle. The quality of the rubber is important, the cheaper products use clay fillers and have an oily substance that can leach out over time, when heat is applied. The result is a pad that will disintegrate over time.

GOOD QUALITY CUSHIONS WILL HAVE A LIFETIME GUARANTEE

Many carpets and pads are approved by their manufacturer for radiant floor heat.