Preventing Problems with Combustion Equipment

Sufficient amounts of Air:

For bathrooms, ASHRAE 62.99 recommends that you exhaust 25 cubic feet per minute (cfm) with a continuously operating fan, or 50 cfm with a fan that you turn on and off as needed.

Note that you might incorporate a bath fan into your overall ventilation strategy.

Read equipment's home owner manual and instructions. Make sure equipment receives regular professional inspection and maintenance.
Avoid installing unvented (or "vent-free") space or water heating appliances.
When replacing heating equipment, consider using only sealed-combustion, induced draft, or power-vented furnaces, boilers, and water heaters.
Use a properly sized range hood fan if you use a gas range.
After installation of combustion and/or ventilation equipment, combustion equipment should be tested to be sure that it functions properly.
Vent clothes dryers to the outside.
Consider installing a Carbon Monoxide alarm.

Combustion appliances are those which burn fuels for warmth, cooking, or decorative purposes. Typical fuels are gas, both natural and liquefied petroleum (LP); kerosene; oil; coal; and wood. Examples include space heaters, ranges, furnaces, fireplaces, water heaters, and clothes dryers. These appliances are usually safe. However, under certain conditions (see below), these appliances can release harmful or deadly combustion pollutants into the home (commonly called combustion spillage or backdrafting). In addition, unvented or improperly vented appliances can add large amounts of moisture to the air, potentially resulting in both biological growth, and damage to the house. Proper selection, installation, inspection, and maintenance of combustion appliances are extremely important. Providing good ventilation can also can reduce exposure to combustion pollutants.

Things to consider when remodeling your home are listed below. For a more complete discussion of combustion appliances, see the following publications:

EPA's What You Should Know About Combustion Appliances
The Department of Energy's Technology Fact Sheet "Combustion Equipment Safety" which provides a more detailed explanation along with installation recommendations.

Read equipment's home owner manual and instructions. Make sure equipment receives regular professional inspection and maintenance.

It is important that you understand how to properly operate combustion equipment in your homes, and that you follow the manufacturer's recommendations for maintaining the equipment. Have your combustion appliances--and your chimney--regularly inspected and maintained to reduce your exposure to pollutants. Appliances that are not working properly can release harmful and even fatal amounts of pollutants, especially carbon monoxide, into the living space.

Avoid installing unvented (or "vent-free") space or water heating appliances.

Unvented appliances leave all combustion products in the house. Even if incomplete combustion pollutants such as carbon monoxide (CO) are kept to a minimum, these appliances can generate large amounts of moisture which can create its own problems. Unvented heaters require special precautions.

Unvented Space Heaters

Take special precautions when operating unvented fuel-burning space heaters.

Consider the potential indoor air pollution effects if you use an unvented kerosene or gas space heater. Follow the manufacturer's directions, especially instructions on the proper fuel and keeping the heater properly adjusted. A persistent yellow-tipped flame is generally an indicator of improper adjustment and increased pollutant emissions. While a space heater is in use, open a door from the room where the heater is located to the rest of the house and open a window slightly.

Learn more about carbon monoxide (CO).

When replacing heating equipment, consider using only sealed-combustion, induced draft, or power-vented furnaces, boilers, and water heaters.

Traditionally, combustion equipment relied on natural draft, the tendency for the warm combustion air to rise up a chimney. Today's more efficient equipment does not waste as much energy or send as much heat up the chimney, weakening natural draft. Natural draft can at times be overcome by conditions that depressurize the house, leading to spillage, backdrafting, and the problems associated with combustion products in the house.

ENERGY STAR equipment usually features sealed combustion or power-venting. The risk of backdrafting is lower with these types of equipment than for those relying on natural draft.

Sealed combustion equipment draws its combustion air directly from outside the home. The combustion products are exhausted directly out of the home. The air intakes and exhaust are sealed off from the inside of the home, and this greatly reduces the change for any spillage of combustion products into the home.

While induced draft and power-vented appliances rely on air in the home for combustion, they use a fan to force pollutants out of the home. This reduces the chance of natural draft being overcome be other fans or pressures in the home.

Use a properly sized range hood fan if you use a gas range.

All kitchens should have exhaust ventilation to remove odors and excess moisture associated with cooking. While there are various ventilation strategies for kitchens, a range hood is the most common. When using a gas range, a range hood directly vented to the outside should be used to capture the combustion products. These range hoods should be sized correctly. For a typical kitchen range the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) and the Home Ventilation Institute (HVI) recommend 100 cfm. Larger fans may need to have makeup air provided to avoid excessively depressurizing the house, causing backdrafting or other problems.

After installation of combustion and/or ventilation equipment, combustion equipment should be tested to be sure that it functions properly.

It is important that your installer conducts a worst-case depressurization test. This combustion safety test determines if any non-sealed combustion appliances will backdraft or spill combustion products into the living space. Tell your installer this test should use an established procedure such as Appendix D of the International Fuel and Gas Code or ASTM E1998 "Guide for Assessing Backdrafting and Spillage from Vented Combustion Appliances"

Vent clothes dryers to the outside.

Always vent clothes dryers directly outside. In addition to combustion products produced by gas dryers, all dryers generate large amounts of moisture and particulates which should be vented out of the house before they have the opportunity to create problems.

Consider installing a Carbon Monoxide alarm.

Carbon monoxide (CO) is a colorless, odorless gas which at high levels can cause serious illness and death. CO alarms are widely available and should be considered a back-up to BUT NOT A REPLACEMENT for proper installation, use, and maintenance of fuel-burning appliances. CO alarms are designed to warn you of any unusual build-up of CO in your home. These higher levels of CO may occur from improperly maintained, installed or used fuel-burning appliances, backdrafting appliances or fireplaces, or idling cars in garages. If a CO alarm is to be installed:

Make sure the device is certified to the most current Underwriters Laboratory (UL) standard 2034 or the International Approval Services (IAS) 6-96 standard.
Install a CO alarm in the hallway near every separate sleeping area.
Be aware of all instructions and warnings associated with the CO alarm.

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