A blower door is a machine used to measure the airtightness of houses. It can also be used to measure airflow between building zones, to test ductwork airtightness and to help physically locate air leakage sites in the houses envelope.

Blower door tests are commonly done on new construction to ensure building standards are met and they are also commonly done as part of an energy assessment, ie. in Ontario we have the energuide rating. Homeowners will often book an assessment before starting a renovation so they can take advantage of any government incentives for improvements made to their home. The auditor will perform the blower door test and do a complete walkthrough to locate problem spots around the house. Often with a renovation their is the possibility for your home becoming to tight after insulation is increased or a new air barrier is installed, this can lead to condensation on your windows and the potential for mould growth. This is why it's equally important to get the test done after the renovation as it is before.