Most of the heat lost in a home occurs through the walls and ceiling due to insufficient loft and cavity wall insulation. Ten percent of a home’s heat is lost through its windows. Monitoring home heat loss involves performing an energy audit. Your utility provider can perform one or you can perform one to determine where air is entering or escaping your home. In addition to an energy audit, check the condition or existence of insulation in your attic, walls and the floors over an unheated basement.

How Much Heat is Being Lost?

Every building loses heat. Thermal heat loss occurs mainly via Conduction and Air infiltration. The percentage of thermal heat loss from a building is also dependent on the ‘form’ (the shape) of the building. The more aspects the more thermal heat loss.

Heat Loss

If you are thinking about building a new house then it is important to know that simplicity in ‘form’ will save you heaps of cash in energy running cost.


  1. Perform a building pressurization test if leaks aren’t visually detectable. Close all exterior doors, windows and fireplace flues. Turn off all combustion appliances like gas-burning furnaces. Turn on all exhaust fans in the kitchen and bathroom or turn on a large window fan to suck air out of the rooms and make air leaks easier to detect. Light a stick or incense or wet your hand and pass either one over walls, around windows, doors, near the ceilings and anywhere air might escape. Leaks will make your hand feel cool and blow away the incense smoke.
  2. Check for open fireplace dampers, which suck a large amount of heat out of the house.
  3. Look for thermal tracking. Thermal tracking appears as dark marks or tracks on interior walls. Warm, moisture-laden air contacts cool walls or a ceiling and gives up some of its moisture as condensation. Some surface areas, particularly those where there are air leaks, become damper than others and airborne debris is trapped on those areas as warm air moves up the walls and over ceilings. Thermal tracking is sometimes misidentified as mold.
  4. Understand U-factor. Windows are measured in U-factor, which is a measure of heat transfer (loss). U-factor takes into account airflow around the window and the emissivity of glass. Single-pane glass has a high emissivity (it radiates energy through itself at a high rate) and will transfer 84 percent of the infrared energy from a warm room outside to the cold air.
  5. Look for a vapor barrier underneath attic insulation in the form of tarpaper, Kraft paper attached to fiberglass batts or a plastic sheet. Vapor barriers prevent large amounts of moisture from passing through the ceiling and increase the effectiveness of the insulation. If there is no vapor barrier, consider painting the ceilings with vapor barrier paint.
  6. Have a thermographic inspection performed to determine where insulation is lacking or needs replacement. This will require hiring an energy auditor, but it is the only real way to determine if whole walls are insulated or if insulation has settled and where insulation improvements need to be made.
  7. Determine whether there is insulation beneath living area flooring over an unheated basement. The U.S. Department of Energy recommends insulation with an R-value of 19 or greater for insulation at the top of the foundation wall and first floor perimeter. Heat losses also occur from warm air passing through ducts in an unheated basement, so insulate heating duct equipment as well.