What is R-Value?
How Does it Apply to Floor Heating?
11/13/2024 - R-value is a measure of insulation against conducted heat. Normally in the United States, R-value is measured in square feet hours per Btu, ( ft ²· ° F · h / Btu ). In simple terms, as R-value goes up, less heat is conducted through the material. Homes are insulated to prevent heat from escaping by raising the R-values of the walls and roof. This applies to electric radiant floor heating because the R-value of the material above and below the heating wire affects the efficiency of the system.
Insulation under the floor heating wire prevents energy from being sucked out into the sub-floor. This ensures that more heat gets to where it will warm you. For this reason the insulation should have a higher R-value. Above the heating element, a lower R-value is needed, otherwise the flooring will prevent heat transfer to your room.
Easy Warm Floor recommends Insulayment underneath our floor heating wires. It is approved for use under both tile and hard wood floor. At only an 1/8 of an inch thick, the R-value of the mat is approximately 2.8. This adds significant insulation without adding significant floor height. While this is a fine R-value, higher R-values can offer additional benefits in colder climates.
Too much of a good thing is not recommended though. Our products are only approved for use with insulating layers with R-values below 19. This is a very high value and will most likely not factor into your floor heating project.
The maximum R-value of the top layer of flooring must not be more than 2.5 to allow effective heat transfer. Flooring with a lower R-value will transfer heat from the wires more freely and increase efficiency. Check with your flooring manufacturer to find out the R-value of your particular flooring.
R-value from outside the US
Outside of the US, R-value is often measured using a different unit, kelvin square meters per watt (K·m²/W). You may well find that some flooring products list the r-value measurements in this unit without labeling it as such. This can be confusing as that is may appear that the insulating effectiveness seems impracticably low. If this is the case you can do an approximate conversion 1 K·m²/W � 5.67446 ft²·°F·h/Btu. Inversely, 1 ft²·°F·h/Btu � 0.1761 K·m²/W.
In these terms the insulation layer must not have an R-value exceeding 3.35 K·m²/W. The layer above the floor heating must in turn not exceed 0.44 K·m²/W.
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