Combustion Safety Testing

A simple, low cost test can determine if there is a current or potential problem with the combusting appliances (gas water heater, gas furnace, gas fireplace, etc) accentuated periodically by vent fans and dryers running at the same time as the appliances.


Testing is the only way to ensure the air quality in the home or apartment is safe from carbon monoxide and other combustion gases.

The potential problems the technicians test for include:

The improper combustion of fuels produces Carbon Monoxide.

  • Carbon monoxide can enter the house if the chimney is blocked or the flue is disconnected, or because exhaust fans in the house are pulling air down the chimney.
  • A depressurized CST can cause flame rollout and back drafting of the flue.
  • A gas leak can cause an explosion.

The CST tests are designed to primarily answer the following:
Is there CO in the ambient air? In the CST? In the flues? In the gas oven? If so, how much? Is it too much?

  • Are there any gas leaks in the gas lines or valves or joints?
  • Do the fumes go out the chimney or the flue quickly? Do any fumes come back into the room? When the water heater or furnace or boiler fires up, do flames come out of the unit?
  • When the CST is depressurized the most by exhaust fans or clothes dryers in the house, do the appliances still draft adequately?
  • Is the pressure in the flue with reference to the CST strong enough to ensure that the appliance drafts?

Websites of Interest

For more information on Indoor Air Quality (IAQ)

CST testing ensures open combustion appliances are not causing unhealthy or hazardous conditions in a home or building.

The EPA (Environmental Protection Agency) describes the forces working to depressurize a home in the figure. They include bathroom exhaust fans, kitchen range hoods, and clothes dryers. Fireplaces, leaky return ducts near combustion equipment, leaky supply ducts outside the conditioned space, wind, and the stack effect (warm air rising in a building tends to depressurize lower areas)are other forces not shown in the diagram.

If these forces are great enough, they can work to suck air and combustion products back down the chimney or flue and into the house, as shown by the red arrows in the diagram.

​Osprey Building Performance technicians are certified by the Building Performance Institute (BPI) and Residential Energy Services Network (RESNET) in CST testing.  They verify proper ventilation and safe operation of combustion appliances by using pressure testing devices, gas leak detectors and CO testing equipment. This ensures that combustion appliances are not leaking Carbon Monoxide (CO) and/ or other combustion gases into the home, apartment or building.

Many apartment complex owners do not see the need for CST because they have not experienced any problems.  What they don’t know is that their tenants may be exposed to low levels of CO and think they have the flu a lot. Exposure to carbon monoxide, even in low parts per million is especially dangerous to pregnant women, children and elderly, but these individuals do not or cannot express or differentiate their health problems and potential causes.