what is the purpose of a threshold
Comstock/Comstock/Getty Images. The threshold is the strip or wood or metal that runs across the bottom of an entry door frame. A threshold is an important factor in the energy efficiency of a home or building.It also has several additional purposes in the doorway. A threshold can be replaced, or improved, if it does not adequately perform its job.here are additional methods to help block the large amount of air that can slip underneath a door, even with a threshold in position. A popular method to stop the draft is to install a metal door sweep along the bottom of the entry door.