What is a blower door?
A blower door is a calibrated testing instrument used to either pressurize or depressurize a building and measure the amount of airflow at a given pressure (usually in pascals), commonly referred to as "ACH." The structure is tested at 50 pascals and referred to as ACH50.
What is "ACH?"
ACH is "air changes per hour." ACH is a universal measurement and requirement for a building to meet state or local requirements. For example, did you know Montana follows the 2018 Internation Energy Conservation Code, which requires less than 4 ACH50? That's four air changes per hour at 50 pascals, which is equivalent to a roughly 20 mile per hour wind blowing at the side of a structure.
AHHH! You're building the house too tight! Houses need to breathe!
These are typical comments, and the science that accompanies this technology has been around for a long time. The first thing to understand is that we're not trying to stop all air movement. The goal is to manage the air. HRV and ERV systems are employed to exchange air from inside and outside through air filters and a heat exchanger. Homes don't need to breathe, but the people inside do! These units supply fresh, clean filtered air, as well as tempering the air that enters the house.