Proper interior ventilation is vital to your family's health and comfort. It helps your home rid itself of moisture, smoke, cooking odors, and indoor pollutants. Structural ventilation controls heat levels in the attic, moderates dampness in the crawlspace and basement, and keeps moisture out of uninsulated walls.
Interior ventilation
Kitchens, bathrooms, and laundries are the biggest sources of moisture and odors. You should have three key exhaust units: an exterior-venting range hood and bathroom and laundry exhaust fans.
Many kitchens have a range hood that doesn't actually vent anything — it just "filters" and recycles stovetop air. It's much better to get rid of the greasy, smoky, steamy air, and that requires ductwork to an exterior vent. If your kitchen is smelly and the walls are covered with a film of grease, you need an exterior-venting exhaust fan. Your favorite appliance retailer can make it happen for you.
Airborne grease makes exhaust fans sticky, which in turn attracts dirt and dust. Clean the grill and fan blades twice a year, or whenever they start to look bad. The filters in recycling range hoods need cleaning every couple of months or so (depending on how and what you cook), and the fan and housing need a good cleaning every six months. If the filters have charcoal pellets inside, they need to be replaced annually. Clean your range hood filter in the dishwasher. For the grill and fan blades, use a spray-on degreaser. Follow with a mild soap and water wash. Finally, flush with fresh water and towel-dry.
Bathrooms generate huge amounts of moisture and some unpleasant odors. If you have incurable mildew in the shower, paint peeling off the walls, or a lingering funky smell, you need to install an exhaust fan or get a bigger, higher-capacity fan. Exhaust fans can vent the bad air through the wall or through the ceiling and attic. Clean the housing and fan at least twice a year.
Structural ventilation
To keep heat and moisture from roasting and rotting your home over time, having adequate ventilation in the attic and the crawlspace (and the basement, if it's unfinished) is important.
In the attic, the idea is to create an upward flow of air. Cool air flows in through vents in the eaves and out through vent(s) nearer to, or at the peak of, the roof. In the crawlspace, cross-ventilation is used.
If insulation, crud, or dead squirrels block the vents, or if there aren't enough vents, the attic and subarea can become tropical. Rot can develop. Condensed water can soak insulation, making it ineffective. Condensation from above and below can make its way into the house, ruining ceiling, floor, and wall finishes and short-circuiting electrical wiring. If you notice that your vents are clogged, clear them immediately.
Roof ventilation
If your attic is hot and humid in the summer, you may need to install additional vents at the eaves and at the ridge of the roof. It's best to leave this to a professional.
Make sure that each vent and screen is painted (to prevent deterioration) and that the screens are secured to the frame of the vent. Badly damaged vents should be replaced. Solid vent screens prevent varmints of all sorts from settling in your attic.
Foundation ventilation
Moist air can cause rot in the crawlspace. If your crawlspace is always overly damp, or if you see mildew on the walls or structure, you may need better ventilation.
Extra vents are difficult to install and require special tools to cut through lumber, concrete block, concrete, and brick. Don't go poking holes in your foundation on your own — call a carpenter or masonry contractor to do the work.
Foundation vents can be damaged in the same way as eave vents. Establish a no-holes policy. Maintain foundation vents in the same way as you maintain eave vents.