CAZ Testing: Combustion Appliance Zone

All natural gas appliances, oil and pellet equipment should be tested for CO levels.

This is to assure that the proper ventilation is taking place and second it tells how efficient or non efficient the device is.

This includes, furnace's, hot water heaters, boilers, stoves, etc.

Backdrafting
Backdrafting is a condition in which air flows down a flue or chimney rather than up, and combustion fumes can’t flow out. The fumes spill into your living spaces.

Backdrafting occurs when the combustion gases can’t go up and out flues and chimneys because outdoor air is already flowing down them. This often occurs when you run a clothes dryer, powerful range fan or any combination of venting fans. All suck air out of your home. If your house can’t get enough makeup air leaking in around windows doors and through cracks and gaps in walls, the makeup air may come down the flues or chimney. Then your furnace, water heater or wood-burning fireplace may not vent properly, and combustion gases, including CO, will spill into your living space. (Studies have shown that backdrafting is common even in homes that are not energy efficient or airtight, so this test is worthwhile regardless of any energy-efficiency improvements you’ve made.)

A complete backdraft test only takes about 10 minutes. The service technician should close all doors and windows and turn on your ventilating fans, creating a worst-case situation. The technician will then turn on your water heater and test it for combustion gas spillage, and test the furnace as well.

If you have significant spillage, the technician should inspect your venting system and recommend solutions.

Preventing Backdrafting of Chimneys

Backdrafting (a.k.a. Combustion Gas Spillage) occurs when a naturally vented appliance loses the chimney effect, which normally carries dangerous combustion by-products (carbon dioxide, nitrogen dioxide and carbon monoxide) up the chimney. Backdrafting can occur with furnaces, fireplaces, woodstoves, and water heaters when air pressure in the house is lower than outside air pressure. Backdrafting is more likely to occur when the wind speed is too low to create suction by the Venturi effect at the top of the chimney.

Running a furnace, clothes dryer, bathroom exhaust fans, or a kitchen exhaust fan can cause the negative indoor air pressure that leads to backdrafting, as they move air out of the house, which must be replaced from the outside. If the doors and windows are all closed and very tight, the replacement air may come down a chimney and can cause backdrafting of combustion appliances.

How do we prevent backdrafting?

Try to start fireplaces and woodstoves when no other devices are removing air from the house. Once a draft is established, it is less likely to change into a backdraft, particularly in a properly vented and maintained device. If possible, have the water heater and furnace draw their intake air directly from the outside. If you see smoke coming back down a chimney, you have a problem that needs immediate attention.

Common Causes

An influx of combustion gases occurs whenever the exhaust system comes under a negative pressure, and thus negative pressure situations are the cause of combustion gas spillage. Negative pressure occurs when indoor air pressure is less than that of outdoor air pressure, drawing outside air into the home. Two different types of forces work on a home and affect air pressure: external forces and internal forces.

External Forces: those that occur naturally and usually are determined by weather conditions. The two major external forces at work on a home are:

[1] Wind, which can cause a positive pressure on the windward side of a house and negative pressure on the leeward side and sides parallel to the flow, affecting a home's pressure balance.

[2] Temperature, which changes pressure because of its effect on air density. If temperatures vary greatly between indoor and outdoor, this can create what is known as the "stack effect" in which cold air enters easily through lower level openings and, once heated, rises and exits through openings in the upper levels of the home. This creates a negative pressure at the lower levels and a positive pressure in the upper ones.

Internal Forces: those which occur within the home to create pressure differences. Any device which has an air exhaust can cause depressurization of a home, including bathroom fans, downdraft cook-top fans, clothes dryers, fireplaces and woodstoves, and fuel fired furnaces or water heaters.

Health Effects

Most commonly, heating appliances will produce by-products of mainly water and carbon dioxide. However, if the combustion from these processes does not have enough oxygen, carbon monoxide is formed, which can be an extreme health hazard even at low concentrations. When natural gas furnaces are used, the carbon monoxide concentration in the exhaust is lower, unless the gases become recycled back through the burner.

However, if heating oil is used instead of natural gas or propane, it will commonly produce high amounts of carbon monoxide. Wood-burning fireplaces and stoves always give off some amount of carbon monoxide, especially during 'ember fires.'

Even if exhaust gas is not a significant problem, spillage may still pose a health risk. When using gas and propane, a major problem is the presence of nitrogen dioxide, which can burn and scar lung tissue even in small quantities. Other problematic pollutants include sulphur dioxide, which creates health risks similar to nitrogen dioxide, and benzene, which is a harmful carcinogen produced in wood smoke.