Guide to increasing the indoor air quality of your home.

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Indoor air quality is becoming an important issue in newer homes since they are being built tighter and allow less air infiltration. Additional precautions need to be taken to insure the health of our families.

Causes of indoor air pollution

Indoor pollution sources that release gases or particles into the air are the primary cause of indoor air quality problems in homes. Inadequate ventilation can increase indoor pollutant levels by not bringing in enough outdoor air to dilute emissions from indoor sources and by not carrying indoor air pollutants out of the home. High temperature and humidity levels can also increase concentrations of some pollutants.

There are many sources of indoor air pollution in any home. These include combustion sources such as oil, gas, kerosene, coal, wood, and tobacco products; synthetic building materials and furnishings as diverse as insulation, wet or damp carpet, and cabinetry or furniture made of certain pressed wood products; products for household cleaning and maintenance, personal care, or hobbies; central heating and cooling systems and humidification devices; and outdoor sources such as radon, pesticides, and outdoor air pollution.

How Does Outdoor Air Enter a House?

If too little outdoor air enters a home, pollutants can accumulate to levels that can pose health and comfort problems. Outdoor air enters and leaves a house by: infiltration, natural ventilation (ex. open windows), and mechanical ventilation (ex. HVAC system). In a process known as infiltration, outdoor air flows into the house through openings, joints, and cracks in walls, floors, and ceilings, and around windows and doors. In natural ventilation, air moves through opened windows and doors. Air movement associated with infiltration and natural ventilation is caused by air temperature differences between indoors and outdoors and by wind. Finally, there are a number of mechanical ventilation devices, from outdoor-vented fans that intermittently remove air from a single room, such as bathrooms and kitchen, to air handling systems that use fans and duct work to continuously remove indoor air and distribute filtered and conditioned outdoor air to strategic points throughout the house. The rate at which outdoor air replaces indoor air is described as the air exchange rate. When there is little infiltration, natural ventilation, or mechanical ventilation, the air exchange rate is low and pollutant levels can increase.

Since the energy crunch of the 1970's builders have been encouraged to build tighter construction for the purpose of conserving energy. In today's tighter homes the air exchange rate is approximately 0.2 to 0.3 air changes per hour (ACH) compared to older homes where air exchange rates have been measured at 2 to 3 air changes per hour. Therefore, as you can see, today's homes are more energy efficient, but also contain higher levels of contaminants in many cases due to less air infiltrating into the building.

It is important to maintain a minimum of 0.35 ACH (air changes/hr.) within the structure for proper indoor air quality. In residential buildings the indoor-outdoor air exchange rate is mainly attributable to air leakage through cracks, joints and other leakage areas and are affected by pressure differentials caused by temperature differences, wind, local exhaust fans, combustion equipment (heating systems, water heaters) and fireplaces. The 0.35 ACH would be considered to be a tight home, anything less is too tight. On the other hand air exchange rates of between 0.35 and 1.0 would be considered to be moderate and above 1.0 ACH is considered to be leaky.

Ideas to consider for reducing indoor pollution

Source Control

Usually the most effective way to improve indoor air quality is to eliminate individual sources of pollution or to reduce their emissions. In many cases, source control is also a more cost-efficient approach to protecting indoor air quality than increasing ventilation because increasing ventilation can increase energy costs. Consider using Green Building materials for construction. These materials are environmentally friendly and do not out-gas pollution into your home.

Ventilation improvements

Another approach to lowering the concentrations of indoor air pollutants in your home is to increase the amount of outdoor air coming indoors. Most home heating and cooling systems, including forced air heating systems, do NOT mechanically bring fresh air into the house. Opening windows and doors and operating window or attic fans, when the weather permits increases the outdoor ventilation rate. Local bathroom or kitchen fans that exhaust outdoors remove contaminants directly from the room where the fan is located and also increase the outdoor air ventilation rate.

Advanced designs of new homes are starting to feature mechanical systems that bring outdoor air into the home. Some of these designs include energy-efficient heat recovery ventilators (also known as air-to-air heat exchangers). It is very important to bring in outdoor air in a controlled method. A simple way of controlling the air infiltration rate is to install a fresh air intake pipe (from the exterior) to the return of your HVAC system; it will draw in fresh air whenever the home is under negative pressure (ex: exhaust fans & clothes dryer running). Therefore the air is heated/cooled & filtered and not being drawn in through the cracks, openings & materials in your home.

Filtration/Air Cleaners

There are many types and sizes of filters & air cleaners on the market, ranging from relatively inexpensive table-top models to sophisticated and expensive whole-house systems. Some air cleaners are highly effective at particle removal, while others, including most table-top models, are much less so. Air cleaners are generally not designed to remove gaseous pollutants.The effectiveness of an air cleaner depends on how well it collects pollutants from indoor air (expressed as a percentage efficiency rate) and how much air it draws through the cleaning or filtering element (expressed in cubic feet per minute). A very efficient collector with a low air-circulation rate will not be effective, nor will a cleaner with a high air-circulation rate but a less efficient collector. The long-term performance of any air cleaner depends on maintaining it according to the manufacturer's directions.For a new HVAC installation, there are many filtration options. Various filter medias, electronic air cleaners, ultraviolet light air purifiers, by-pass HEPA filters, etc. Click my other page for formation on HVAC filtration options.

Additional information on IAQ can be found on these other sites: Environmental Protection Agency (EPA) American Lung Association

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