Indoor Air Quality

The quality of indoor air is a concern to energy and environmental researchers as well as consumers. Since we spend up to 90% of our time indoors in winter, maintaining a clean indoor environment is important. Consumers should become aware of how the products they bring home, such as furniture and carpeting, can affect their indoor environment.

Homeowners want to use energy efficiently and reduce their fuel bills. Many have added insulation, vapor barriers, caulk and weatherstripping to their homes to effectively retain heated or cooled air and reduce air infiltration from outside. Therefore, air remains inside longer and so do pollutants within the air.

Air changes

Air infiltration rates for homes vary with the amount of weatherization, construction materials, workmanship, temperature, wind, and activities of the occupants. Infiltration rates are measured in air changes per hour (ACH), the number of times each hour that indoor air is replaced by outside air. Rates differ from house to house and from day to day. Generally, older homes have an average of one to two ACHn. Tight, new homes or older homes which are sealed may replace air only once every hour or more (or .5 ACHn.)

Be aware of these signals which may indicate poor indoor air quality:

  • "stuffiness"
  • frequent head or chest colds
  • mold or mildew
  • a musty smell or lingering odors
  • heavy condensation or frost on windows

Sources of Pollution and General Control Measures

  • Consumer product
    • Cleaning solutions, aerosol sprays, glues, paints and polishes contain a variety of pollutants such as formaldehyde, chlorine, etc. Be sure to follow manufacturer’s directions when using these products. If the directions state, "use in a well-ventilated area," try to use it outdoors. Or, open doors and windows during and after use to allow pollutants to escape.
  • Building material
    • Glues containing urea-formaldehyde are found in many building materials used in home and furniture construction. These materials slowly release formaldehyde which can cause eye or nose irritation and headaches. In new construction, use low-formaldehyde materials and cover with latex-based paint to prevent formaldehyde release.
    • Insulation made from urea-formaldehyde releases formaldehyde through leaks and cracks in walls and ceilings. Caulking leaks and cracks on the interior surface will prevent release into the living area.
    • In the past, asbestos was used as insulation in attics, walls and around furnace pipes. Today asbestos is no longer allowed because of evidence it can cause illness. If your home has asbestos-type insulation, it is best left undisturbed. However, soft, easily-crumbled asbestos-containing materials have a greater potential for asbestos release and should be professionally sealed. Whenever it is necessary to use or work with asbestos-containing materials, consult a professional.
  • Garage - Exhaust from a gasoline-fueled car contains such pollutants as carbon monoxide, lead and nitrogen dioxide. Never run or warm up a car in an attached or enclosed garage, even if the garage door is open; pollutants can enter the home, causing nausea and even death if allowed to build up.
  • Bathrooms are a source of moisture. When moisture is not allowed to escape, water damage, mold and mildew may develop. Install a bathroom exhaust fan for ventilation, or open a nearby window slightly when bathing or showering.
  • Fuel-burning appliances
    • When burned, fuels such as wood, coal, fuel oil, charcoal and kerosene produce water vapor, carbon dioxide, heat, smoke and other pollutants. When natural gas is completely burned, it produces water vapor, carbon dioxide and heat (the same products human beings exhale.) For any fuel to burn completely, an adequate supply of combustion air is necessary.
    • Your home normally exhausts air through flues, fans, cracks, etc. When air leaves the home, it must be replaced by outside air. Generally, outside air is provided through cracks and leaks. But, when insufficient outside air is supplied to the house, replacement air may be pulled down chimneys, preventing proper venting of furnace flue products (water vapor and carbon dioxide). The flue products will then mix with indoor air and reduce the amount of available oxygen. This causes the fuel to burn incompletely and may produce carbon monoxide.
    • It is important that enough fresh air be available for complete combustion. This becomes especially critical when indoor air changes are reduced due to weatherization. An outdoor air intake can be installed in the heating system for efficient and proper operation. See Minnegasco’s Combustion Air fact sheet for more information.
    • All furnaces, wood-burning stoves, space heaters, water heaters and gas logs must be vented to the outside. Follow manufacturer’s directions and check local codes before installing. Inspect vent/chimney periodically to make sure it is tight, clean and in good repair.
    • A range hood can be installed to exhaust steam and cooking vapors.
  • Smoking - Tobacco smoke contains many pollutants. If there is a smoker in your home, adequate ventilation becomes an even greater health issue.

How to Improve the Indoor Environment

There are many ways to add ventilation or filter the air to improve the indoor environment.

  • Windows - When heating and cooling requirements are low, open windows to provide ventilation and reduce moisture and odors caused by cooking and bathing.
  • Spot ventilation - Local or spot ventilation helps reduce the amount of pollutants emitted and prevents their movement to the rest of your house. For example, a range hood directs steam and cooking vapors to the outside.
  • Air-to-air heat exchanger mechanically ventilates and dehumidifies homes in colder climates. During the winter it transfers heat from the air being exhausted, to the fresh, outside air entering the home. Fifty to eighty percent of the heat normally lost in exhausted air is returned to the house. Air-to-air heat exchangers can be installed as part of a central heating and cooling system or in walls or windows. Wall and window-mounted units resemble air conditioners and will ventilate one room or area. They are easy to install.
  • Conventional or mechanical furnace filters - Filters are coated with a viscous substance to collect dust, lint and fibers. These range from low to high efficiency in ability and capacity for filtering pollutants from the air. Clean or replace as needed.
  • Electronic furnace filters (air cleaners) - Air is cleaned as it moves through a series of mechanical filters and electronically charged plates, chambers or filters which hold dust like a magnet. These are more efficient in removing pollutants from the air than conventional filters. Follow manufacturer’s directions for cleaning.

House as a System

Whole House Diagnostic

Home Performance

Carbon Monoxide