Glossary · Testing & air leaks
Combustion appliance zone (CAZ)
The room or area holding a fuel-burning appliance such as a furnace, boiler or water heater; it's the focus of combustion safety testing.
What it means
The CAZ is usually a basement, utility room, closet or garage. Auditors measure the air pressure there compared with outdoors, check carbon monoxide levels and test each appliance's draft, because the pressure in this space decides whether exhaust goes up the chimney or back into the house.
Why it matters in an audit
Air sealing, a new exhaust fan or simply closing the furnace-room door can change CAZ pressure enough to cause backdrafting, so it's tested before and after work.