Combustion Products from Heating Appliances: Indoor Air Quality Hazards
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Flue gas hazards from heating equipment
Combustion product gas hazards: carbon monoxide, nitrogen dioxide, sulphur dioxide (sulfur dioxide), soot and combustion particles
INDOOR AIR QUALITY IMPROVEMENT, KEY STEPS
Questions & answers about flue gases & combustion products produced by burning home heating oil, natural or LP gas, wood or wood pellets, or coal in home heating appliances

This article explains flue gases and particles produced by various heating appliances and their impact on safety and indoor air quality in homes.

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What are the Products of Burning Heating Oil, LP Gas, Natural Gas, What is in "Flue Gases" and What are the Hazards?

This article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.

See our summary table of INDOOR COMBUSTION PRODUCTS & IAQ and see ENVIRONMENTAL HAZARDS - INSPECT, TEST, REMEDY for our full list of environmental hazard identification and remedy related to buildings. See COMBUSTION AIR for additional details about the requirement for combustion air. COMBUSTION AIR for TIGHT buildings explains how to provide outside combustion air for tight buildings. See COMBUSTION GASES & PARTICLE HAZARDS for an explanation of the dangers of inadequate combustion air. See COMBUSTION PRODUCTS & IAQ for the relationship between fuel burning appliances and building indoor air quality. More about carbon monoxide - CO - is at CARBON MONOXIDE - CO and at CARBON MONOXIDE WARNING.

As stated in Best Practices Guide to Residential Construction:

A combustion appliance is any device that burns fuel for heating, cooking, or decorative purposes. This includes central-heating systems, space heaters, water heaters, ovens and cooktops, woodstoves, and fireplaces. The major pollutants associated with combustion are carbon monoxide, nitrogen dioxide, sulfur dioxide, and particles. See INDOOR COMBUSTION PRODUCTS & IAQ for a Table of Combustion Products & Indoor Air Quality Hazards that accompanies this article.

Unvented space heaters and gas stoves without range hoods dump combustion products directly into the living space and have no place in the modern home. Vented appliances, such as boilers, water heaters, and fireplaces, are designed to exhaust combustion products to the outdoors, but they are vulnerable to backdrafting in today’s tightly built houses. When appliances are malfunctioning or out of adjustment, they produce more pollutants, including carbon monoxide. The combination of backdrafting and the high production of carbon monoxide can be deadly.

Health Effects of Combustion Products. Possible health effects from combustion products include eye and respiratory irritation, persistent coughing, headaches, fatigue, and dizziness. In the case of carbon monoxide, symptoms can include nausea and confusion, and, at very high levels, loss of consciousness and death. Effects associated with specific pollutants are discussed below:

Carbon monoxide. CO is a colorless, odorless gas produced by incomplete combustion. Common sources include blocked chimneys or vents, cracked or rusted heat exchangers, poorly adjusted appliances, smoldering fireplaces, and auto exhaust from an attached garage.
CO interferes with the blood’s ability to deliver oxygen to the body. Low concentrations may increase chest pain in people with heart disease. Sustained concentrations above 70 ppm can cause fatigue, headache, weakness, and nausea, and may be confused with the flu or food poisoning.

Fetuses, infants, the elderly, and people with anemia or heart disease are especially vulnerable. At very high levels, CO causes confusion, loss of consciousness, and death. CO alarms are programmed to sound before levels reach 100 ppm for 90 minutes, 200 ppm over 35 minutes, or 400 ppm over 15 minutes.

see CARBON MONOXIDE - CO for details about carbon monoxide standards, exposure, testing, and remediation.
Nitrogen dioxide. NO2 is a colorless gas with an acrid odor at high levels.

T he primary source of NO2 in homes is unvented gas and kerosene space heaters, gas stoves without a range hood, and stoves with continuously burning pilot lights. Studies have shown that homes with unvented gas appliances have elevated NO2 levels, and there is some evidence linking this with impaired lung function and increased respiratory infections in children. At high levels, NO2 is an eye, nose, and respiratory irritant.

Children and people with asthma and other respiratory problem are more susceptible to exposure. Common Indoor Pollutants and Sources 293

see Nitrogen Oxides Gas for details.
Sulfur dioxide. SO2 is a colorless gas with a pungent odor and is primarily associated with oil- and coal- burning appliances. At low levels of exposure, SO2 can cause eye, nose, and respiratory tract irritation. At high exposures, it can cause the airways to narrow, leading to chest tightness and breathing problems. People with asthma are particularly susceptible to SO2 exposure. See Sulfur Dioxide Gas.
Particles. The health effects of breathing particles depend on several factors, including the size and chemical makeup of the particles.

In general, suspended particles can cause eye, nose, and throat irritation, and increased respiratory symptoms for people with chronic lung or heart disease. In addition, a number of pollutants, including the carcinogens radon and benzo(a)pyrene, attach themselves to small particles and are then inhaled and carried deep into the lungs.

Guide to Reducing Exposure to Combustion Gases & Particles Indoors

The three main sources of combustion products in household air are unvented appliances, appliances or flues that are broken or poorly adjusted, and backdrafting. To minimize exposure, follow these general guidelines:

Unvented space heaters. Do not use unvented space heaters in living spaces. If required for temporary use, closely follow manufacturer’s directions, open a window, and open doors to adjoining rooms. A persistent yellow-tipped flame is generally an indicator of poor adjustment and increased pollutants.
Cooking. With gas ranges and cooktops, always use a range hood vented to the exterior. Choose appliances with electronic ignition rather than a continuously burning pilot light. Or replace with electric appliances.
Sealed combustion. In new construction, avoid the use of atmospherically vented boilers, furnaces, or water heaters. Instead, use power-vented appliances, preferably with sealed combustion.
Inspections and maintenance. Have central heating systems and water heaters inspected and adjusted annually. Inspect all flues and chimneys for blockages or damage and promptly repair any problems.

Blocked or leaking chimneys or flues can result in serious illness or death from carbon monoxide poisoning. See DRAFT HOODS - gas fired for gas fired heating equipment, and see DRAFT REGULATORS, DAMPERS, BOOSTERS for oil fired heating equipment. Also see GAS MEASUREMENT TOOLS for a discussion of gas leak testing instruments.
Woodstoves. Make sure doors in older woodstoves are tight fitting with intact gaskets. New stoves should meet EPA emissions standards. Burn only seasoned wood. Make sure there is adequate air for combustion and that the house is not depressurized by exhaust fans (see Backdrafting and also page 295 of Best Practices Guide to Residential Construction).
Fireplaces. Fireplaces should have inserts with tight- fitting doors and a dedicated outside air supply. Fireplaces should not be used if the house is depressurized by exhaust fans (see Backdrafting and also page 295 of Best Practices Guide to Residential Construction, by Steven Bliss, Wiley & Sons).

-- Adapted with permission from Best Practices Guide to Residential Construction.

See INDOOR COMBUSTION PRODUCTS & IAQ for a Table of Combustion Products & Indoor Air Quality Hazards. At CHIMNEY INSPECTION DIAGNOSIS REPAIR we discuss chimney inspection and diagnosis including unsafe venting and fire hazards.

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InspectAPedia.com^® - Daniel Friedman - Publisher & Editor.
Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education. Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com.
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CHIMNEY INSPECTION DIAGNOSIS REPAIR
COMBUSTION AIR
COMBUSTION AIR for TIGHT buildings
COMBUSTION GASES & PARTICLE HAZARDS
COMBUSTION PRODUCTS & IAQ
COMPLETE COMBUSTION, Stoichiometric

Carbon Monoxide Gas Toxicity, exposure limits, poisoning symptoms, and inspecting buildings for CO hazards
DUST CONTAMINATION FROM HVAC? An Investigation of Indoor Dust Debris Blamed on a Heating/Cooling System Reveals Carpet Dust
Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
"Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
"Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
Installation Guide for Residential Hydronic Heating Systems
Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)
Goodman Furnace High Temperature Plastic Vent HTPV safety recall US CPSC notice
Home Heating System Should Be Checked [for proper venting and for CO Carbon Monoxide Hazards - DJF]
Inspection Procedures for Oil-Fired Heating Systems Detailed step by step approaches for inspecting complex systems]
Lennox Pulse Furnace Safety Inspection/Warranty Program: Carbon Monoxide Warning
Plastic Heating Vent Pipe & Other Heating Safety Recall Notices
Weil McLain Model GV Gas Boiler/gas valve CPSC recall/repair

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Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
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What are the Products of Burning Heating Oil, LP Gas, Natural Gas, What is in "Flue Gases" and What are the Hazards?

Guide to Reducing Exposure to Combustion Gases & Particles Indoors

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