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Improving Indoor Air Quality In Your Home

by Mark Segal
This article appeared in the July 2001 edition of AAIA Ontario News.

There are numerous factors in a home that can affect the health of its occupants. This article is designed for the allergic/asthmatic to highlight some of the most important.

Factors are presented in a general order of theoretical and logical priority. In the real world, however, priorities for your home may vary depending on problems unique to your home or budget: can you afford to attack indoor air quality in the whole home, or do you want to start with the allergic/asthmatic's bedroom? In either case, you will likely need the advice of a specialist in home inspection to help you prioritize your interventions.

Whether you decide to go big or small in correcting indoor air quality (IAQ), a general rule of thumb remains the AAIA's "3A's" approach:
Awareness - know what's causing your IAQ problem
Avoidance - remove sources causing your IAQ problem
Action - when IAQ can't be corrected by source removal alone, add mechanical devices to correct problems.

Too Much Humidity: Controlling Mould and Dust Mite Growth
Mould and dust mite allergens can be the cause of many breathing symptoms, especially for the allergic/asthmatic. High humidity causes mould and dust mites to multiply and thus is a priority focus for correction throughout the many places in the home these can grow.
Mould is often detectable to the naked eye (e.g., black spots on wood window frames, bathroom tiles, carpeting and walls). Other potential mould growth areas are in ventilation equipment such as air conditioning coils, humidifiers, air exchanges coils and dehumidifiers.

Basements are notorious for mould and dust mite problems. Being below ground level increases the possibility of water infiltration. This can be due to structural problems whereby the protective membrane between the earth and the foundation wall fails to prevent water from seeping through. Old homes that have had their windows upgraded were not designed to be airtight and can trap humidity, leading to mould growth in the areas of the home mentioned above.
How do you fix high humidity? Proper ventilation all year round is crucial for controlling the problem.

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Proper Ventilation and Pressurization: Controlling Humidity
In the winter, it is best to keep the humidity level between 35-40%. Over 40% encourages dust mite and mould growth. Homes in which newer, more hermetically sealed windows have been installed may require the installation of an air exchanger or heat recovery ventilator for fall and winter to ensure that the humid air created by bathing, cooking and washing does not build up in the home. Exhaust fans are required in bathrooms where bathing and showering can trap humidity. Make sure to have adequate cubic feet per minute of exhaust for the size bathroom being serviced.

Summer: The use of a standard air exchanger or heat recover ventilator will not be effective enough in lowering summer humidity because the air outside is too humid at this time of year. The only possible function of an air exchanger during the warmer season would be to continue to ventilate the home with the windows and doors kept closed for long period of time.
In summer, a portable, wall-mounted or central air conditioning or a heat pump are necessary to lower humidity in indoor air. These control the humidity level by condensing the air. It is possible to dehumidify a home during the summer months using an active heat recovery ventilator that is designed to condense the air. These are more costly units than your standard air exchanger or heat recovery ventilator and are for people who do not like cooling their home but would like to dehumidify or temper the air during the summer months.

Controlling Comfort
Ventilation can affect your comfort level in the home. Too cold in one room, too hot in another; too much air in one room, not enough in another. This is when you must call in a ventilation expert to try to balance the air circulation as best possible.

Controlling Pressurization
A more serious problem is back drafting from fireplaces. This occurs when potentially toxic particulate from the fireplace returns into the home instead of moving up through the chimney. Again, consulting with a professional in ventilation to determine if your home is pressurized properly will ensure safe use of your fireplace.

Not Enough Humidity: Enhancing the Body as an Air Filter
When people complain of irritated throats, itchy or chapped skin or blocked noses, they may be living in a home with an insufficient amount of humidity. These symptoms are not synonymous with low humidity, however. Other factors such as poor air filtration, toxic gases, mould or dust mite allergens can also lead to these symptoms.
To verify if low humidity is a problem in your home, it is recommended that you buy a humidity gauge. If humidity is less than 30-35%, it tends to dry out body fluids in the upper and lower airways, moisture that is needed to filter air particles we breathe. You will need to purchase either a humidifier that attaches to a central ventilation system or strategically place portable units.

The type of portable humidifier that treats the water by boiling it is recommended. If a central unit is preferred, either a flow-through, padless drum type, or a steam humidifier will be better than the old drum and pad type units where water sits in a pan and soaks on the sponge, sometimes for days.
As mentioned earlier, however, humidifiers can be a breeding ground for mould. Where there is moisture, mould will begin to form in a short time. When standing water is not removed within 72 hours, mould growth will occur rapidly and minor problems can quickly become major. Make sure to be well informed on the maintenance required to keep your humidifier in good repair and to clean it thoroughly during and at the end of the low humidity season (in Canada, usually winter).

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Filtration is extremely important to breathing healthier air. You need a filter than can capture very small airborne particles - those particles which the human body cannot filter. Reducing airborne particles enhances recuperation of the respiratory system during a good night's sleep.
Of all the filters available on the market, only certain ones are designed to actually trap very small particles (i.e., down to 0.3 microns). Electronic filters do so noiselessly and very well, but beware. Their efficiency decreases with use and they thus require regular and frequent cleaning to maintain filtering performance over time. Electronic filters are known to produce ozone, a potent respiratory irritant, as a by-product of being dirty. Keeping them clean at all times is critical.

In recent years, the most recommended and popular filtering system for asthma/allergy sufferers is a "media filter" system called HEPA (high efficiency particulate arrester). This filter medium will continuously capture very small airborne particles and become even more efficient over time. It requires no cleaning and does not produce ozone. HEPA units are available for central installation or for single room use.
To make sure a HEPA unit is as good as a manufacturer says it is, ask for a demonstration using a particle counter capable of measuring concentrations of particles as small as 0.3 microns in size (1/25000 of an inch). If the air coming out of the unit does not capture 99.97% of particles 0.3 microns in size, the system does not meet true HEPA performance criteria.
There are other media-type filters available on the market that are less efficient than HEPA, but it is important that every home has a filter on its ventilation system. A good rule of thumb when buying a less efficient throw-away filter is - if salt can pass through, it is not worth purchasing.

Decontaminating Ventilation Equipment
Most people never think to clean their ventilation equipment. That is because not many people, including professionals in the business of ventilation, are aware that cleaning equipment and products exist to safely and effectively perform this task. There are many products available that claim to completely disinfect a ventilation system. Sadly, many of these products are made of toxic solutions that can be harmful to the upper and lower airways. Moreover, the difficulty of applying the product thoroughly renders them unreliable.

Decontaminating your ventilation system or portable ventilation equipment is like going to the dentist to have your teeth cleaned. Both are meant to protect against build-up of harmful substances. While cleaning your teeth lessens the likelihood of gum disease, decontaminating equipment lowers the risk of breathing contaminated air, particularly with moulds.
Treating your ventilation equipment (air conditioning and heating systems, portable and wall A/C units, dehumidifiers, humidifiers and heat recovery ventilators) against mould and bacteria growth before it reaches levels of toxicity that can adversely affect your health is crucial to maintaining good air quality. This work can be done in minutes, safely, using non-toxic products.

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Other Indoor Air Pollutants to Watch Out For
1) Off-Gassing of Toxic Fumes: Try to reduce use of toxic cleaners - go "green" (nontoxic).
2) Household Clutter: Reducing household clutter makes it easier to clean your home and help reduce dust mite buildup
3) Pets: Deciding on whether or not to keep a pet is always a difficult subject. Tough decisions from time to time must be made when compromised health of a loved on becomes an issue. If you have pets, keep them away from bedrooms. Keep them clean and vacuum frequently with either a HEPA filtered system or central vacuum that exhausts to the exterior of the home.
4) Smoking: Smoking of tobacco products in the home should be avoided at all times. Second-hand or environmental tobacco smoke (ETS) can lead to asthma in young children. For up to a half-hour after smoking, the smoker's exhalations continue to pollute the spaces s/he occupies.
5) Incorrect Cleaning Procedure: When using a standard filtered vacuum, pollutants sucked from the carpet go through the filter and escape into the ambient air. Vacuuming should be done only with an approved HEPA filter or central vacuum system which exhausts its air to the exterior. When dusting, use an implement that traps particles instead of stirring them up.

What are the factors that improve indoor air quality?

Proper dehumidification.
Air exchanges and heat recovery units should only be in operation for the purpose of dehumidification when a lower humidity level outside will help reduce the humidity level inside. Note that in summer, the only way to dehumidify a home is by condensing the air. Air conditioning is recommended. Install exhaust fans when necessary in bathrooms and kitchens.

Proper Ventilation
Balance temperatures and relative humidity as best possible throughout the home with ventilation equipment.

Proper Pressurization
Make sure your home is not in negative pressure (looking for air, or trying to suck it in from the outside through openings such as fireplaces).

Proper Humidification
Keep humidity between 35-40%. Use a portable or central system that either produces humidity with steam or does not use standing water and is easy to clean.

Proper Filtration
There are two levels of filtration - one for the ventilation system (standard performance filter capable of filtering visible dust and dirt) and one to protect the human respiratory system (such as a high performance media filter capable of filtering particles down to 0.3 microns in size).

Proper Maintenance / Decontamination
Periodically, decontaminate and clean equipment using nontoxic solutions that can effectively treat all areas including the duct distribution. Verify mechanical performance by a trained professional.

Reduce Toxicity in the Home
Use nontoxic cleaning products Make your home smoke-free.

Clean your Home Regularly
Vacuum and dust with technology that captures rather than stirs up particles from surfaces. Remove or consider not introducing sources of potential allergens. These include: carpeting, pets, stuffed animals, fabric (e.g., upholstered furniture, drapes).

Getting Help
Improving and maintaining good indoor air quality is a challenge. Establishing a relationship with a qualified specialist in home inspection is critical in meeting it. For help finding someone qualified in your area, contact:
The Heating, Refrigeration and Air Conditioning Institute of Canada (HRAI)
5045 Orbitor Drive, Building 11, Suite 300
Mississauga, ON L4W 3Y4
Tel: 1-800-267-2231 or (905) 602-4700
Web site:

HRAI is a partnership of industry sector organizations that represents Heating, Ventilation, Air Conditioning and Refrigeration (HVACR) manufacturers, wholesalers and contractors who provide the Canadian public with products and services for indoor comfort and essential refrigeration processes.

Terms of Use: The information on this site does not constitute medical advice and is for your general information only. We cannot be held responsible for anything you could possibly do or say because of information on this site.   Consult your family physician or allergist for specific questions or concerns.

This article courtesy of the Allergy/Asthma Information Association at and the Calgary Allergy Network web site at May be reproduced for educational, non-profit purposes.
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