Installing a fan in your kitchen or bathroom is a good idea becuase you will be able to efficiently evacuate moisture, heat and stale smelly air from these rooms. Stale smelly air is unpleasant. Moisture can cause damage to your house, and also can be a nuisance. Excessive heat is unpleasant, especially in the summertime. The downside to installing a fan is that if your house is fairly airtight  and you don't provide adequate supply air, you might end up sucking nasty air through all sorts of cracks and crevices in your house.

When selecting your fan, one thing to consider is how much noice the fan will make. Most products on the market are given a noise rating in sones. Generally a quieter fan is nicer, but some prople prefer a noisy bathroom fan because it hides embarrassing bathroom noises.

Fans are generally also rated according to the amount of air they move in cubic feet per minute (CFM.) Some care should be taken to size the fan properly according to the size of the room and the amount of heat, moisture or smells of fish frying that need to be evacuated. Typical kitchen hoods and fans move from 300 CFM to 1200 CFM, and bath fans are typically 40-100 CFM.