What You Should Know About Combustion Appliances and Indoor Air Pollution

Consumer Product Safety Commission

What You Should Know About Combustion Appliances and Indoor Air Pollution

CPSC Document #452

Hazards may be associated with almost all types of appliances. The purpose of this booklet is to answer some common questions you may have about the potential for one specific type of hazard - indoor air pollution - associated with one class of appliances - combustion appliances.

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 of the appliances are space heaters, ranges, ovens, stoves, furnaces, fireplaces, water heaters, and clothes dryers. These appliances are usually safe. However, under certain conditions, these appliances can produce combustion pollutants that can damage your health, or even kill you.

POSSIBLE HEALTH EFFECTS range from headaches, dizziness, sleepiness, and watery eyes to breathing difficulties or even death. Similar effects may also occur because of common medical problems or other indoor air pollutants.

This booklet was written:

  1. to encourage the proper use, maintenance, and installation of combustion appliances;
  2. to discuss the pollutants produced by these appliances;
  3. to describe how these pollutants can affect your health; and,
  4. to tell you how you can reduce your exposure to them.

Should I be concerned about indoor air pollution?

YES. Studies have shown that the air in our homes can be even more polluted than the outdoor air in big cities. Because people spend a lot of time indoors, the quality of the air indoors can affect their health. Infants, young children and the elderly are a group shown to be more susceptible to pollutants. People with chronic respiratory or cardiovascular illness or immune system diseases are also more susceptible than others to pollutants.

Many factors determine whether pollutants in your home will affect your health. They include the presence, use, and condition of pollutant sources, the level of pollutants both indoors and out, the amount of ventilation in your home, and your overall health.

Most homes have more than one source of indoor air pollution. For example, pollutants come from tobacco smoke, building materials, decorating products, home furnishings, and activities such as cooking, heating, cooling, and cleaning. Living in areas with high outdoor levels of pollutants usually results in high indoor levels. Combustion pollutants are one category of indoor air pollutants.

What are combustion pollutants?

Combustion pollutants are gases or particles that come from burning materials. The combustion pollutants discussed in this booklet come from burning fuels in appliances. The common fuels burned in these appliances are natural or LP gas, fuel oil, kerosene, wood, or coal. The types and amounts of pollutants produced depend upon the type of appliance, how well the appliance is installed, maintained, and vented, and the kind of fuel it uses. Some of the common pollutants produced from burning these fuels are carbon monoxide, nitrogen dioxide, particles, and sulfur dioxide. Particles can have hazardous chemicals attached to them. Other pollutants that can be produced by some appliances are unburned hydrocarbons and aldehydes.

Combustion always produces water vapor. Water vapor is not usually considered a pollutant, but it can act as one. It can result in high humidity and wet surfaces. These conditions encourage the growth of biological pollutants such as house dust mites, molds, and bacteria.

Where do combustion pollutants come from?

Combustion pollutants found indoors include: outdoor air, tobacco smoke, exhaust from car and lawn mower internal combustion engines, and some hobby activities such as welding, woodburning, and soldering. Combustion pollutants can also come from vented or unvented combustion appliances. These appliances include space heaters, gas ranges and ovens, furnaces, gas water heaters, gas clothes dryers, wood or coal-burning stoves, and fireplaces. As a group these are called "combustion appliances."

What is a vented appliance?
What is an unvented appliance?

Vented appliances are appliances designed to be used with a duct, chimney, pipe, or other device that carry the combustion pollutants outside the home. These appliances can release large amounts of pollutants directly into your home, if a vent is not properly installed, or is blocked or leaking.

Unvented appliances do not vent to the outside, so they release combustion pollutants directly into the home.

Look at the box below for typical appliance problems that cause the release of pollutants in your home. Many of these problems are hard for a homeowner to identify. A professional is needed.


Appliances Fuel Typical Potential Problems
Central Furnaces
Room Heaters
Natural or
Petroleum Gas
Cracked heat exchanger;
Not enough air to burn fuel properly; Defective/blocked flue; Maladjusted burner
Central Furnaces Oil Cracked heat exchanger;
Not enough air to burn fuel properly;
Defective/blocked flue; Maladjusted burner
Central Heaters
Room Heaters
Wood Cracked heat exchanger; Not enough air to burn fuel properly; Defective/blocked flue; Green or treated wood
Central Furnaces
Coal Cracked heat exchanger; Not enough air to burn fuel properly; Defective grate
Room Heaters
Central Heaters
Kerosene Improper adjustment; Wrong fuel (not-K-1); Wrong wick or wick height; Not enough air to burn fuel properly
Water Heaters Natural or
Petroleum Gas
Not enough air to burn fuel properly; Defective/blocked flue; Maladjusted burner
Ranges; Ovens Natural or
Petroleum Gas
Not enough air to burn fuel properly; Maladjusted burner; Misuse as a room heater
Not enough air to burn fuel properly; Defective/blocked flue; Green or treated wood; Cracked heat exchanger or firebox

Can I use charcoal grills or charcoal hibachis indoors?

No. Never use these appliances inside homes, trailers, truck-caps, or tents. Carbon monoxide from burning and smoldering charcoal can kill you if you use it indoors for cooking or heating. There are about 25 deaths each year from the use of charcoal grills and hibachis indoors.

NEVER burn charcoal inside homes, trailers, tents, or other enclosures. The carbon monoxide can kill you.

What are the health effects of combustion pollutants?

The health effects of combustion pollutants range from headaches and breathing difficulties to death. The health effects may show up immediately after exposure or occur after being exposed to the pollutants for a long time. The effects depend upon the type and amount of pollutants and the length of time of exposure to them. They also depend upon several factors related to the exposed person. These include the age and any existing health problems. There are still some questions about the level of pollutants or the period of exposure needed to produce specific health effects. Further studies to better define the release of pollutants from combustion appliances and their health effects are needed.

The sections below discuss health problems associated with some common combustion pollutants. These pollutants include carbon monoxide, nitrogen dioxide, particles, and sulfur dioxide. Even if you are healthy, high levels of carbon monoxide can kill you within a short time. The health effects of the other pollutants are generally more subtle and are more likely to affect susceptible people. It is always a good idea to reduce exposure to combustion pollutants by using and maintaining combustion appliances properly.

Carbon Monoxide:

Each year, according to CPSC, there are more than 200 carbon monoxide deaths related to the use of all types of combustion appliances in the home. Exposure to carbon monoxide reduces the blood's ability to carry oxygen. Often a person or an entire family may not recognize that carbon monoxide is poisoning them. The chemical is odorless and some of the symptoms are similar to common illnesses. This is particularly dangerous because carbon monoxide's deadly effects will not be recognized until it is too late to take action against them.

Carbon monoxide exposures especially affect unborn babies, infants, and people with anemia or a history of heart disease. Breathing low levels of the chemical can cause fatigue and increase chest pain in people with chronic heart disease. Breathing higher levels of carbon monoxide causes symptoms such as headaches, dizziness, and weakness in healthy people. Carbon monoxide also causes sleepiness, nausea, vomiting, confusion, and disorientation. At very high levels it causes loss of consciousness and death.

Nitrogen Dioxide:

Breathing high levels of nitrogen dioxide causes irritation of the respiratory tract and causes shortness of breath. Compared to healthy people, children, and individuals with respiratory illnesses such as asthma, may be more susceptible to the effects of nitrogen dioxide.

Some studies have shown that children may have more colds and flu when exposed to low levels of nitrogen dioxide. When people with asthma inhale low levels of nitrogen dioxide while exercising, their lung airways can narrow and react more to inhaled materials.


Particles suspended in the air can cause eye, nose, throat, and lung irritation. They can increase respiratory symptoms, especially in people with chronic lung disease or heart problems. Certain chemicals attached to particles may cause lung cancer, if they are inhaled. The risk of lung cancer increases with the amount and length of exposure. The health effects from inhaling particles depend upon many factors, including the size of the particle and its chemical make-up.

Sulfur Dioxide:

Sulfur dioxide at low levels of exposure can cause eye, nose, and respiratory tract irritation. At high exposure levels, it causes the lung airways to narrow. This causes wheezing, chest tightness, or breathing problems. People with asthma are particularly susceptible to the effects of sulfur dioxide. They may have symptoms at levels that are much lower than the rest of the population.

Other Pollutants:

Combustion may release other pollutants. They include unburned hydrocarbons and aldehydes. Little is known about the levels of these pollutants in indoor air and the resulting health effects.

What do I do if I suspect that combustion pollutants are affecting my health?

If you suspect you are being subjected to carbon monoxide poisoning get fresh air immediately. Open windows and doors for more ventilation, turn off any combustion appliances, and leave the house. You could lose consciousness and die from carbon monoxide poisoning if you do nothing. It is also important to contact a doctor IMMEDIATELY for a proper diagnosis. Remember to tell your doctor that you suspect carbon monoxide poisoning is causing your problems. Prompt medical attention is important.

Remember that some symptoms from combustion pollutants - headaches, dizziness, sleepiness, coughing, and watery eyes - may also occur because of common medical problems. These medical problems include colds, the flu, or allergies. Similar symptoms may also occur because of other indoor air pollutants. Contact your doctor for a proper diagnosis.

To help your doctor make the correct diagnosis, try to have answers to the following questions:

Your doctor may take a blood sample to measure the level of carbon monoxide in your blood if he or she suspects carbon monoxide poisoning. This sample will help determine whether carbon monoxide is affecting your health.

Contact qualified appliance service people to have your appliances inspected and adjusted if needed. You should be able to find a qualified person by asking your appliance distributor or your fuel supplier. In some areas, the local fuel company may be able to inspect and adjust the appliance.

How can I reduce my exposure to combustion pollutants?

Proper selection, installation, inspection and maintenance of your appliances are extremely important in reducing your exposure to these pollutants. Providing good ventilation in your home and correctly using your appliance can also reduce your exposure to these pollutants.

Additionally, there are several different residential carbon monoxide detectors for sale. The CPSC is encouraging the development of detectors that will provide maximum protection. These detectors would warn consumers of harmful carbon monoxide levels in the home. They may soon be widely available to reduce deaths from carbon monoxide poisoning.


Proper Installation

You should have your appliances professionally installed. Professionals should follow the installation directions and applicable building codes. Improperly installed appliances can release dangerous pollutants in your home and may create a fire hazard. Be sure that the installer checks for backdrafting on all vented appliances. A qualified installer knows how to do this.


Correct Use

Inspection and Maintenance

What are the inspection and maintenance procedures?

The best advice is to follow the recommendations of the manufacturer. The same combustion appliance may have different inspection and maintenance requirements, depending upon where you live.

In general, check the flame in the furnace combustion chamber at the beginning of the heating season. Natural gas furnaces should have a blue flame with perhaps only a slight yellow tip. Call your appliance service representative to adjust the burner if there is a lot of yellow in the flame, or call your local utility company for this service. LP units should have a flame with a bright blue center that may have a light yellow tip. Pilot lights on gas water heaters and gas cooking appliances should also have a blue flame. Have a trained service representative adjust the pilot light if it is yellow or orange.

Before each heating season, have flues and chimneys inspected and cleaned before each heating season for leakage and for blockage by creosote or debris. Creosote buildup or leakage could cause black stains on the outside of the chimney or flue. These stains can mean that pollutants are leaking into the house.

The chart below shows how and when to take care of your appliance.

This booklet discussed the types of pollutants that may be produced by combustion appliances, described how they might affect your health, and suggested ways you could reduce your exposure to them. It also explained that proper appliance selection, installation, operation, inspection, and maintenance are very important in reducing exposure to combustion pollutants.


Appliance Inspection/Frequency Maintenance/Frequency
Gas Hot Air Heating System Air Filters - Clean/change filter - Monthly As needed;
Look at flues for rust and soot - Yearly
Qualified person check/clean chimney, clean/adjust burners, check heat exchanger and operation - Yearly (at start of heating season)
Gas/Oil Water/Steam Heating Systems and Water Heaters Look at flues for rust and soot - Yearly Qualified person check/clean chimney, clean combustion chamber, adjust burners, check operation - Yearly (at start of heating season)
Kerosene Space Heaters Look to see that mantle is properly seated - daily when in use;
Look to see that fuel tank is free of water and other contaminants -- daily or before refueling
Check and replace wick -- Yearly (at start of heating season);
Clean Combustion chamber -- Yearly (at start of heating season);
Drain fuel tank -- Yearly (at end of heating season)
Wood/Coal Stoves Look at flues for rust and soot - Yearly Qualified person check/clean chimney, check seams and gaskets,
check operation -- Yearly (at start of heating season)

For more information:

For a copy of CPSC's booklets What You Should Know About Space Heaters and What You Should Know About Kerosene Heaters, and for information on asbestos, biological pollutants, lead, methylene chloride, humidifiers, and formaldehyde in your home, write to:

U.S. Consumer Product Safety Commission
Washington, D.C. 20207 or send an e-mail to publications@cpsc.gov.

For a copy of The Inside Story: A Guide to Indoor Air Quality, and additional information on indoor air quality call:

EPA's IAQ INFO Clearinghouse
P.O. Box 37133, Washington, DC 20013-7133
1-800-438-4318, or (703) 356-4020
(fax) (703) 356-5386, or e-mail: iaqinfo@aol.com

Information on indoor air quality is also available from local American Lung Association (ALA)

For information on woodstoves write:

Wood Heater Program
U.S. Environmental Protection Agency
Manufacturing, Energy, and Transportation Division (2223A)
401 M Street, SW
Washington, DC 20460
(202) 564-2300/(202) 564-0050 (fax)

For information on kerosene heaters, write or call:

National Kerosene Heater Association
3100 West End Avenue, Suite 250
Nashville, TN 37203
(Telephone: 615-269-9015)

For information on gas heating appliances, write:

Gas Appliance Manufacturers Association, Inc.
1901 North Moore Street, Suite 1100
Arlington, VA 22209

American Gas Association
1515 Wilson Blvd.
Arlington, VA 22209

For a copy of Straight Answers to Burning Questions or other woodburning information, write:

Wood Heating Alliance
1101 Connecticut Ave NW, Suite 700
Washington, DC 20036

The CPSC and the EPA have not reviewed or approved all the information and documents on indoor air quality that may be provided by other groups or organizations.

Any reproduction should credit the American Lung Association, the U.S. Consumer Product Safety Commission, and the U.S. Environmental Protection Agency. The use of all or any part of this document in a deceptive manner or for purposes of advertising or endorsing a particular product may be subject to appropriate legal action.