How to Find Heat Loss in an Attic Roof

The attic is one of the areas of greatest heat loss in a home. Heat loss is generally measured in BTUs per hour, the same system used to rate the power of furnaces and boilers. Calculating how much heat you lose hourly can be useful when purchasing a new heating system or determining whether it's necessary to improve your insulation.

Instructions

- 1
  Measure the width and length of each flat surface on the roof. Multiply each pair of numbers and add the results together.
- 2
  Find the U-value of the materials that make up the roof and ceiling of the attic. A material's U-value is its capacitance, the degree to which it allows heat to pass through it. The U-values of many common building materials can be found online (see Resource for link).
- 3
  Find the temperature in the attic and subtract the lowest annual outdoor temperature from it.
- 4
  Multiply the area, U-value and temperature difference. The result is the hourly heat lost through the attic roof, measured in BTUs.

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