The quality of your indoor air is important, and one way to keep it good is to ventilate the moist air and odours created in kitchens and bathrooms. This is important in all homes, but especially so in newer construction, since new homes are built to have good insulation and tight air seals that prevent air movement.
This leads to a decrease in fresh air circulation, which leads to a stagnant environment, condensation on windows, flaking paint and mould growth. The best solution is to buy and professionally install ventilation fans.
Delicious aromas may be part of good cooking, but we don't always want the odours from one meal to linger around until the next, or for them to spread further into additional living areas. As well, the by-products of cooking - moisture, grease, heat and even carbon monoxide (from gas range combustion) - can be dangerous.
In my opinion, hood fans that exhaust back into the house, even if they are filtered, have limited effectiveness. They don't really take the heat and moisture or cooking odours anywhere, they just move it around.
Bathrooms create odours, too, but the moisture they can generate is potentially far more serious, since the average shower produces an enormous amount of water vapour and steam. If that warm, wet air isn't properly vented, it will find its way into your walls and ceilings and cause a lot of problems.
After your shower, make sure you run that exhaust fan for 20 or 30 minutes. Don't make the mistake of just running it for a few minutes and thinking the job is done. Get one on a timer so you don't have to remember.
Also, you need to keep the door or a window open a bit when the fan is running. If the bathroom is sealed while the fan is on, there is not enough air present to properly exchange it, and the fan can't push the moist air outside. If the airflow in your bathroom is restricted, your fan's power will be reduced significantly.
Take it outside
Whatever you do, don't vent your fans into the attic - they need to send air directly outside. The moisture and heat will help create the perfect conditions for mould to grow, and grow quickly. I've seen the damage that can result from ventilation fans releasing air into attics, walls, ceilings or roof soffits. It causes rot that can destroy your home's structure.
There's a good reason it is completely against building code to vent exhaust systems into attics - it's critically important to vent to the outside, to get rid of moisture.
Make sure you buy and correctly install the right fans for the job. You can test your fan's strength by holding a tissue up to it when it's on. If the fan's suction will hold the tissue in place, it's fine; if not, replace the fan.
For bathrooms up to 100 square feet, an exhaust fan should provide a minimum of 1 cubic foot per minute (CFM) per square foot of floor space. I'd go higher, especially in a larger bathroom, or one with several fixtures or a jetted bathtub.
A kitchen range hood moves more air than a bathroom fan and they tend to be louder depending on the speed they are set to. Usually, an average size range requires air removal at the rate of 120 CFM for an overhead vent hood.
But be careful not to overdo it; high-capacity exhaust fans and range top fans can cause chimney backdrafting. This occurs when air is drawn down into the chimneys, potentially bringing dangerous combustion exhaust gases into the house.
If you have these high-draw fans you will need a matching supply-air fan to balance house pressure.
Make sure your contractor installs the fan so the ducting has as short and straight a run to the outside as possible. If the exhaust duct has to turn or go a long distance, you might want to consider a fan with a larger capacity.
The best exhaust paths are made using solid, smooth ducting, not ribbed or flexible, which can impede air flow. And, where the ducting runs through unheated spaces, you have to make sure they are properly sealed at every seam, and insulated. Without it, the cold air surrounding the ductwork will cause condensation and leaks.
You should clean your exhaust fans twice a year. Just remove the cover and check it for dust build-up. You'll be surprised how much has collected, and that dust reduces your fan's performance significantly.