Not much, as it turns out. To illustrate this point, Ted Haskell, Oregon State University Extension Agent, put together the following calculation. It's not a rigorous engineering equation, but it will give you a good idea of the heating load associated with exhaust-only ventilation. The procedure appears on this page with an example filled in. Remember this is just an estimate.
Many factors can affect the outcome from the actual air leakage of the house to the climate.
Choices for several key factors, including building air leakage, heating degree days and heating system efficiency, appear in the box at the bottom of this page. Air Tightness One way to express the air tightness of a house is air changes per hour, which is the number of times the amount of air inside the house changes in one hour. The air leakage in a house is usually measured with a blower door. In many areas, you can find a specialist to conduct the test for you. Check with electric utilities, heating contractors, insulation contractors and home inspectors.