Ventilation gets pollutants out of the house

Houses need to breathe. They need to be able to expel the moisture, stale air and, in some cases, the toxic gases generated by heating and cooking equipment.

In the past, homes were drafty enough to vent these pollutants to the outside. However, recent improvements in building methods have led to airtight houses. These new energy-efficient homes are sealed so well, there is no way for pollutants to escape.

Unless airtight homes are properly vented, these pollutants can build up and, in the worst-case scenario, lead to illness or cause premature deterioration of building products.

The solution is simple. Remove the stale air and replace it with fresh air from the great outdoors.

Airtight homes will probably require a whole-house ventilator. The American Society of Heating, Refrigerating and Air Conditioning Engineers recommends a house undergo 0.35 air changes each hour, but not less than 15 CFM for each occupant, whichever is less, CFM refers to the amount of air in cubic feet per minute that is moved through a mechanical exhaust system.

If you're researching ventilation systems, you'll notice the CFM ratings are listed in the manufacturers' specification sheets. Note that the actual air flow, once the system is installed, my be lower than specified due to ducting. This is because air flowing through a duct leading to the outside loses force with every turn or bend.

If your house isn't airtight (and most aren't), a whole-house mechanical ventilation system isn't required. Ventilating the attic, kitchen and bathrooms will usually do the trick.

Attic ventilation

It's extremely important to ventilate your attic. The goal is to keep the temperature in the attic equal to the temperature outdoors by establishing a constant air flow through the space. Without ventilation, an attic can easily reach 65 degrees Celsius on a summer day - hot enough to split a shingle.

During the winter, condensation can rust fasteners and rot wood framing. There are a number of venting systems available. For example, combining roof-ridge vents with soffit vents relies on the natural movement of air. The air enters through the lower soft it vents, rises to the ridge and is vented out.

Gable fans feature aluminum louvres that open when the fan is on and close when it's off. Some models are equipped with a humidistat that switches the fan on when a predetermined amount of moisture is present in the attic.

Kitchen ventilation

The kitchen is a major source of pollution in the home. Grease, smoke, undesirable odors and some toxic emissions from gas ranges can linger in a room that's poorly ventilated.

Most homeowners wouldn't think about lighting a fireplace without first opening the flue, but aren't that concerned about planning a kitchen with an ineffective ventilation system. A recirculating system is a filtration system, not a ventilation system.

Contaminates are forced through filters. A metal mesh collects grease particles, a glass fibre filter removes smoke and a charcoal filter removes odor. Recirculating systems should not be used with a gas range because they don't remove combustion gases.

A range ventilation system captures air containing grease, smoke, odors and combustion gases and is exhausted to the outdoors. This results in cleaner surfaces and improved air quality in the home. Check the CFM rating before purchasing a new range hood.

The following are typical airflow rates:
Range hood 150 600 CFM
Island hood 400.600 CFM Microwave hood 200 - 400 CFM
Downdraft unit 300 - 500 CFM

The range hood should be mounted 21 inches above the range. Ideally, a hood is more efficient if it extends three inches past the range on each side. A 30-inch range should be paired with a 36 inch hood.

Bathroom ventilation

Without ventilation, moisture condenses on walls, ceiling, counters, etc. High moisture levels can cause paint and wallpaper to crack and peel, warp doors and promote mildew growth.

Ceiling and wall ventilators should be placed close to the bathtub or shower. Bathroom fans should be powerful enough to make -,eight air changes in one hour. You figure out the appropriate CFM . rating by multiplying the square footage of the room by 1.1.