Design Temperature Difference (DTD)

Change the DTD to the one in your area. This represents the average coldest weather in your area, not the record coldest temperature. The numbers are compiled for ASHRAE and appear in their publications.

Accurately completed heat estimates are always higher than the actual heat lost from a home, as people using electricity are giving heat to the home. There will be less than a week in several years when the heat lost at night might match the estimate. A heat estimate is done assuming that it will be the average coldest night in the year when the building is unoccupied and electricity is not used for appliances and lights.