Glossary · Testing & air leaks

Combustion safety test

Also called: combustion safety testing · combustion safety check · CAZ test · CAZ testing · combustion appliance test

A check that furnaces, boilers, water heaters and stoves burn cleanly and vent their exhaust outside, even with fans running.

What it means

The auditor measures carbon monoxide (CO) in the flue and in the room, checks the draft in the chimney or vent and looks for spillage or backdrafting. The toughest version, a worst-case depressurization test, turns on exhaust fans and closes doors to see if venting still works. It's done before and after air sealing because a tighter house leaves less air for fuel-burning appliances.

Why it matters in an audit

It protects your household from carbon monoxide, and a failed test becomes a must-fix item ahead of any energy upgrade.

Typical numbers

Reference values with their sources. Your auditor’s report gives the figure for your own house.

What	Value	Source
US EPA outdoor CO standard (NAAQS)	9 ppm (8-hour average); 35 ppm (1-hour average)	epa.gov ↗
Typical CO in US homes without gas stoves (EPA)	0.5–5 ppm	epa.gov ↗

In the United States

Many US auditors follow test procedures and pass/fail limits in BPI's ANSI/BPI-1200 standard.

Sources

Learn more here

Related terms

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.
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.
Carbon monoxide (CO) A colorless, odorless gas from incomplete burning of fuel; it reduces the blood's ability to carry oxygen and can kill at high levels.
Draft (chimney draft) The upward pull in a chimney or vent that carries exhaust out of the house; weak or reversed draft lets combustion gases spill indoors.
Depressurization When more air is being pushed out of a house than is coming in, so the inside sits at slightly lower pressure than outdoors.
Air sealing Blocking the hidden gaps where air leaks in and out of a house, which cuts drafts, heating and cooling costs, and moisture problems.
Natural-draft (atmospherically vented) appliance A furnace, boiler or water heater that takes combustion air from the room and relies on hot exhaust rising up a chimney, so house pressure can reverse it.
Sealed-combustion (direct-vent) appliance A furnace, boiler, water heater or fireplace that brings in combustion air from outdoors through its own pipe and vents exhaust straight outside.

← Every term, A to Z