When installing a heated floor under carpet, it is important to consider the thermal resistance of the materials used. The overall thickness of any materials above the heater, including underlays and overlays, should be taken into account. The carpet should be at least 1/4" thick but no more than 1" thick. The underlay should have low thermal resistance, and the carpet should be hessian backed for efficient operation of the system. Felt underlay should be avoided as it may hinder the performance of the system. Any type of carpet padding can be used as long as it has a density of 6 pounds per cubic foot or more. Most good quality rebounded polyurethane and prime polyurethane have a density of 8 pounds per cubic foot or more. The R-value of the carpet over the foil heater should not be greater than 1. Underfloor heating can be used with carpet flooring, but certain considerations need to be taken into account. The type of carpet, tog ratings, and carpet underlay can impact the efficiency of the heating system. However, using carpet with underfloor heating has benefits such as making a room feel cozy and reducing the circulation of dust compared to radiators. Certain types of carpet, such as those with hessian backing instead of rubber, are recommended for use with underfloor heating. Thick carpets may not allow the heat to travel effectively. The article discusses the importance of choosing the correct carpet for a heated floor system. It mentions that the insulation provided by the carpet can reduce the efficiency of the heating system. To determine if a carpet is suitable for underfloor heating, the article advises checking its tog rating, which is a measure of thermal resistance. The combined value of the carpet and underlay should not exceed 2.5 tog, and preferably less than 1.5 tog for systems with a heat pump. The article provides an example of a carpet with a tog value of 1.23. It also suggests seeking advice from both Nu-Heat design engineers and carpet suppliers when using thick wool and nylon carpets. The article concludes that if the overall tog rating, including the carpet underlay, exceeds 2.5 tog, the underfloor heating system may not perform effectively.