How Does Insulation Affect the Loss of Heat?

Heat Transfer

• Regions of unequal heat will, lacking the intervention of other forces, attempt to equalize their temperatures. During cold winter days, this results in heat loss from your home, as the heat inside tries to match the outside temperature. The greater the inequality between the two, the more rapidly the heat escapes. Insulation's purpose is to slow this heat transfer and preserve the artificial temperatures inside the house.

Thermal Resistance

• Insulation's strength is measured as an R-value, which is the degree of thermal resistance it provides. The higher the number, the more effective the insulation is and the less heat escapes through it. If you divide 1 by a type of insulation's R-value, you obtain its U-value, or capacitance. This is the degree to which the insulation allows heat to escape -- the two numbers are always inverse.

Calculating Heat Loss

• You can find how much heat escapes through your insulation by multiplying its U-value by its area by the temperature difference between the inside and the outside of the building. A 20-foot by eight-foot section of wall with two-inch fiberglass insulation, for example, which has a U-value of 0.12, will lose 288 BTUs of heat per hour given an internal-to-external temperature difference of 15 degrees Fahrenheit.

Calculating Heat Preservation

• To see how much heat your insulation is preserving, you can simply subtract your actual losses from the amount of heat that would be lost given no insulation whatsoever, namely, a U-value of 1. Given an uncovered aperture of the above dimensions and using the example temperature difference, such a non-wall would lose 2,400 BTUs per hour -- the insulation is preventing 2,112 BTUs from escaping every hour.