Floor Systems

Electric radiant heating is fairly common in bathroom floors, especially those with ceramic or marble tile. There are electric radiant products that can be installed below almost any floor, including hardwood and carpet. Wires can be laid in tracks that hold them in place until the concrete or mortar is poured. There are also premanufactured sheets, called matting, that can be laid on the floor before the mortar and tiles are laid.

Some systems put the wires in the actual underlayment to be installed beneath a floating floor system. Others systems place the individual wires or mat material on the sub-floor where a shallow coat of thin set or floor leveler is poured. Underlayment and floor planks are installed above it. Glue at the joints of the floor planks is recommended if the locking system alone cannot hold the floating floor in place. Nails can damage the wires and are not recommended.

Another system sold primarily for retrofit work, puts the heating wires under the subfloor with un-faced batt insulation or rigid insulation panels between the wires and the air space below. Heat trapped between the floor and insulation radiates through the floor to the room above.

Primary or Secondary Heating

Many floor systems are rated at 10-12 watts per square foot or 35 – 40 BTU/hr./sq. ft. (One watt is about 3.4 BTU/hr.) Floor temperatures for normal operation should be 80-90 degrees Fahrenheit. These systems are considered secondary heat. Systems that are capable of 20 watts/sq.ft. are considered primary heat.

Here’s a typical thermostat in a bathroom with in-floor electric radiant heating.

Electric heat is, for the most part, relatively straightforward to inspect. The big issues are electrical safety and adequacy of heat.

*Schematic courtesy of Carson Dunlop