High efficiency furnaces frequently include variable speed fan control to save energy and improve comfort. Variable speed fan motors* save energy by starting up slowly and operating for much longer “on” cycles at much slower speeds. In addition to energy savings, comfort is enhanced by maintaining temperature much closer to set point by eliminating the big temperature swings associated with simple on / off fan control.
Improved Indoor Air Quality is an additional benefit made possible by increased air circulation. The much longer fan run times better utilize a furnace’s air filtration system. (Critical Note: Be sure to change filters regularly).
If improved comfort and air quality are not enough, variable speed furnaces are also much quieter because they operate at slower speeds. While most homeowners like the silent comfort, some people actually complain that they can’t “tell if my furnace is even on”.
* These motors are referred to as “ECM” – Electronically Commutated Motors.