Electric radiant floor heating market today offers consumers a variety of products with different sizes, features and specifications. One of the distinctive differences between products offered is the amount of heat in Watts per square foot generated by the system.
Since BTU (British Thermal Unit) is a more commonly accepted measure, Watts per sq.ft can be converted to BTU using the following formula:
1 Watts/sq.ft = 3.41 BTU/(hour*sq.ft) or
1 BTU/sq.ft = 0.29 (Watts*hour)/sq.ft
12W per sq.ft systems are most common and both floor heating mats and cable sold at HeatTechProducts.com output this amount of energy. If represented in BTU’s, 12W/sq.ft equals approximately to 41 BTU/(h*sq.ft).
There are also 15W/sq.ft systems available and their main difference with 12W systems is the extra 3 Watts (10.2 BTU/(h*sq.ft)) produced by the electric heating cable.
The question, of course, is which system is better for a particular application. The most significant determining factor in this case is the heat loss associated with the room where radiant heated floor will be installed. Heat loss calculations are best done by a professional, but there’s also plenty of DIY tools and software available.
For a prevailing majority of projects in the United States, 12W/sq.ft electric floor heating system is sufficient to serve as a single, primary source of heat. However, if the climate is too cold or building is old, has poor insulation or has a significant number of glass doors or windows, this heat output may not be sufficient. (Read more - "4 common issues with electric RFH systems and how to avoid them")
There are (2) basic solutions to this problem. One is to get 15W/sq.ft system if the additional heat output of 10 BTU’s/sq.ft meets the demand for heat. The other is to space the HeatTech electric heating cable closer than the standard 3”. Reducing the cable spacing from 3” to 2”, for example, will increase the heat output by an impressive 33%, resulting in about 55 BTU’s/sq.ft heat output.