Soot and oil burner combustion product leak (C) Daniel Friedman Combustion Products from Heating Appliances: Indoor Air Quality Hazards

  • COMBUSTION PRODUCTS & IAQ - Hazardous Gases & Combustion Products of Burning Heating Oil, LP Gas, Natural Gas
    • Flue gas hazards from heating equipment
    • Combustion product gas hazards: carbon monoxide, nitrogen dioxide, sulphur dioxide (sulfur dioxide), soot and combustion particle
  • FURNACES & IAQ - separate article
  • POST a QUESTION or READ FAQs 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

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Hazardous products of oil or gas heating appliance fuel combustion: 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?

Debris in a stack pipe (C) Daniel FriedmanThis article includes excerpts or adaptations from Best Practices Guide to Residential Construction, by Steven Bliss, courtesy of Wiley & Sons.

Our photo left shows a heavy collection of soot and debris in an oil burner flue. What is in oil or gas burner exhaust or combustion products?

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:

Leaky flue (C) Daniel Friedman
  • 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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