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Combustion Safety Testing


The two major reasons for conducting combustion safety tests on your house are for your health (potential carbon monoxide exposure and poisoning) and your safety (fire prevention) for you and your family.  When fossil fuels don’t burn efficiently, carbon monoxide (CO) is formed.  High levels of carbon monoxide are a sign that your combustion appliances are not operating efficiently, and they are dangerous for you and your family.  According to the Centers for Disease Control and Prevention, carbon monoxide poisoning needlessly takes more than 500 lives  every year.


The low down on Carbon Monoxide

Combustion appliances that we are concerned with include improperly vented fuel-burning furnaces, boilers, water heaters, space heaters, fireplaces, gas ranges and ovens.  We are also concerned with CO emissions from vehicles and tobacco smoke.

Combustion safety tests are performed using specialized tools and equipment such as a digital manometer, combustion gas tester, gas leak detector, and smoke pencil or generator.  The tests are designed to answer the following questions:

  1. Is there CO in the ambient air within the home?  In the combustion appliance zone (CAZ)?  In the flue gases? In the gas oven? If so, how much? Is it too much?
  2. Are there any gas leaks in the gas lines, valves or joints?  Are there any hazardous or unsafe conditions?
  3. Do the fumes go out of the chimney or flue quickly?  Is there spillage or back drafting of these fumes when the natural-draft appliances such as water heater,  furnace or boiler are fired up?  Is there evidence of flame rollout?
  4. Under worst-case depressurization (explained below), do the appliances still draft adequately?

Air is exhausted outside the house when we use bathroom exhaust fans, vented kitchen range hoods, or vented clothes dryers.  To compensate for this air loss new replacement air has to be brought in to replace what is being exhausted out.   If all exterior doors and windows are closed and the building envelope is tightly sealed, that new replacement air is likely to enter the house through the chimney and flues.  At the same time if the water heater or furnace comes on when the outside air is coming down the flue, the flue gases can enter the house.  This pressure imbalance can also occur when ducts are leaky or sealed, and when interior doors are opened or closed.  The worst-case scenario of a particular house is reached when the measured pressure in the combustion appliance zone (CAZ) with reference to the outside has the largest negative number.  This is called the worst-case depressurization.

The Building Performance Institute (BPI) action levels specify the safe limits for CO permissible in the flue gases; the minimum acceptable draft pressure in flue pipes with respect to the CAZ; and the maximum negative pressure that is acceptable in the CAZ.  The BPI rules provide guidance on what to do if these levels are exceeded or not met (depending on the test).