Combustion Appliance Zone Testing

Combustion Appliance Zone testing, or CAZ testing, is an important piece of a complete Home Energy Audit. Denver Energy Audit specialists performing a complete Home Energy Audit will perform CAZ testing on your appliances. CAZ testing is important because the health and safety of your family depends on these appliances working properly. Carbon monoxide is a poisonous gas that can kill people and other animals. Infants and the elderly are most susceptible to CO poisoning however it can also affect a healthy individual. In the United States, there are over 400 deaths per year attributed to CO poisoning. Tests of appliances in the combustion zone check to see that there is no leakage of flammable fuel or gases into the living space. CAZ testing should be performed before and after weatherizing a home.

There can be many problems with appliances in existing homes, especially older homes. Older homes typically have older combustible appliances and ventilation systems that may not be up to the current standards for safety and performance. Appliances that most typically cause CO leaks are fuel-burning furnaces, boilers, and water heaters, space heaters, fireplaces and gas ranges and ovens. All of these appliances must be tested during CAZ testing.


There are some easily identifiable CAZ issues that are apparent to the naked eye. Flame roll-out, spillage, and disconnected flue pipes are some of the most common visually diagnosed problems. Signs of flame roll-out are evident because there is a burning of the appliance from the bottom upwards. Roll-out sometimes looks like rust, but if you see this on your appliance, it's time to call a professional. Spillage is also seen at the bottom of appliances. Spillage causes corrosion at the bottom of the appliance and the floor beneath. Flue pipes are important for venting out dangerous gases. If the flue pipes become disconnected or are too short to reach the chimney or vent pipe, gasses are leaked into the home. Other combustion appliance problems can't be easily seen. They are not diagnosed by a visual inspection and test must be performed to find them. Home Energy Auditors will use tools to test the appliances. One such tool is a smoke stick, or smoke tracer. By watching the path that the smoke takes, technicians can tell if appliances are venting dangerous gases properly.

CAZ testing before and after any weatherizing by Denver insulation companies or  HVAC work will keep you family safe. If fuels are not burning properly, CO is formed and Carbon monoxide can enter the house. If the combustion appliance zone is depressurized it can cause flame roll-out and gas leaks leading to catastrophic explosions.

A properly executed CAZ Test will answer these important questions:

1. Is there CO in the homes ambient air? Is there CO in the CAZ? If so, how much?
2. Are there any gas leaks in the lines, valves or joints?
3. Does the chimney or flue ventilate fumes quickly? Is there any backdraft? When the water heater, furnace, or boiler is turned on do flames come out of the unit?
4. When the CAZ is depressurized do the appliances still draft adequately?
5. Is the flue's pressure strong enough to ventilate the appliances in the CAZ?

Proper testing is essential. Tests can be a matter of life and death. Protect your family and your home by scheduling CAZ testing before and after any changes to you HVAC equipment or weatherizing.