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What is combustion spillage?

Combustion spillage is the term used to describe the unwanted flow of combustion gases (from combustion appliances) into your home. Having these gases in one’s home can lead to problems ranging from nuisance headaches to serious illness, carbon monoxide poisoning and even death. The specific Combustion Spillage test City Green conducts is called an Exhaust Devices Depressurization Test.

When should you have a Combustion Spillage Test?

A Combustion Spillage Test (CST) should be considered when:

• Mid-efficiency, non-sealed, or non-directed-vented space or water heating appliances are present.
• Carbon monoxide alarms are sounding.
• Older combustion appliances are present that may have cracks in ducting or heat exchangers.
• Requested by a Building Inspector.
• Occupants have repeated flu-like symptoms (could be potential sign of CO exposure).
• House feels “stuffy” when coming in from outdoors.
• Indoor relative humidity is consistently over 50% during heating season.
• Condensation builds up on windows.
• Occupants notice drafts when exhaust fans are operating.
• Pilot lights blow out for no apparent reason.
• Soot build-up is noticed on or around heating system or water heater.
• Recent significant air sealing work on the home.
• Recent significant changes or additions to ventilation devices (new range hood, bathroom ventilation fans, etc.).

Why does combustion spillage occur?

When air is removed through exhaust devices such as ventilation fans, kitchen range hoods or even internal vacuum systems, the overall pressure of your home is lowered and air from the outside moves in to replace it. Ideally, this air enters the home through properly sized return air vents, though it will also seep in through unsealed cracks. Some houses may be sufficiently “tight” (have reduced outside air infiltration) to the point where there is insufficient make-up air to replace exhausted air. If an exhaust device (kitchen or bathroom exhaust fan, clothes dryer) is turned on under these conditions, it could depressurize the house and cause the chimney of any combustion device to act as an air intake. This is called back-drafting and means that outside air will come down the chimney. If a combustion device turns on when the chimney is back-drafting, the airflow may not reverse back up the chimney and the combustion device will spill its combustion products into the house.

Why is combustion spillage a concern?

Combustion gases can contain toxic compounds including carbon monoxide (CO). Carbon monoxide can result from incomplete combustion of fuels or other carbon-containing materials. Having these gases in one’s home can lead to problems ranging from nuisance headaches to serious illness, carbon monoxide poisoning and even death.

The symptoms of long-term, mild CO poisoning are similar to those of the common flu; often victims do not recognize the true cause. There is only a small difference between a harmless concentration of CO and concentrations that can result in unconsciousness or death. All homes should have a CO sensor/alarm installed, ideally with a digital readout showing concentration levels.

What is a Combustion Spillage Test?

Just like there are several causes of combustion spillage, there are also several different tests that can be performed. The specific Combustion Spillage test City Green conducts is called an Exhaust Devices Depressurization Test. This test is completely safe and involves utilizing a pressure-sensitive measuring device to compare the internal pressure of the house before and after activating all ventilation fans in the home (bathroom fan, range hood, etc.). The resulting pressure measurement indicates if your home is safe, or at risk from combustion spillage due to inadequate ventilation make-up (fresh) air.

The results of the test are noted in a signed, customized report that indicates whether your home has passed or failed the combustion spillage test and provides specific recommendations on how to address combustion spillage issues. The test takes approximately 20-30 minutes to complete and the report will be completed on-site at the time of the visit.

A combustion splillage test costs $150*. When combined with a home energy assessment that allows you to access LiveSmart BC grants for energy efficient upgrades, you recieve a combustion spillage test and report and a customized retrofit plan report for $225*.  

*tax not included. Mileage and other fees may apply.

Combustion Spillage Tests are not needed if:

CSTs do NOT need to be performed if the home has no gas, oil or wood burning heating appliances (all electric).

CST is generally NOT required if the home has new sealed-combustion heating equipment. Sealed-combustion heating equipment uses a double-flue setup to receive combustion air from and vent exhaust gases to, the outdoors. Two concentric pipes – one for air intake and one for exhaust - lead from the appliance to the outdoors. As a result, unless the system has been damaged, there is almost no danger of back-drafting and heated air in the home is not lost.