Glossary · Testing & air leaks

Depressurization

Also called: negative pressure · house depressurization · depressurized · depressurisation

When more air is being pushed out of a house than is coming in, so the inside sits at slightly lower pressure than outdoors.

What it means

Exhaust fans, clothes dryers, range hoods, fireplaces and chimneys all remove air, and in a tight house the replacement air has to come from somewhere, sometimes down a chimney or flue. A blower door test depressurizes the house on purpose to measure leaks; in everyday life, depressurization is what can cause backdrafting of fuel-burning appliances.

Why it matters in an audit

Auditors check it during a combustion safety test because it can pull carbon monoxide into living space, and the same pressure difference can draw soil gases such as radon indoors.

Sources

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Related terms

Backdrafting and spillage When exhaust from a furnace, boiler, water heater or fireplace comes back into the house instead of going up the chimney or vent.
Worst-case depressurization test A combustion safety check run with exhaust fans on and doors set to create the lowest pressure the furnace room is likely to see.
Make-up air Outdoor air deliberately brought into a house to replace air removed by big exhaust fans, range hoods, dryers or fireplaces.
Combustion safety test A check that furnaces, boilers, water heaters and stoves burn cleanly and vent their exhaust outside, even with fans running.
Blower door test A test that uses a powerful, calibrated fan in an outside doorway to pull air out of the house and measure how leaky it is.
Radon A natural radioactive gas from uranium in soil and rock that can build up in homes; long-term exposure raises the risk of lung cancer.

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