Fan exhaust capacity is rated in litres per second (L/s) or cubic feet per minute (cfm). A normal bathroom needs a good-quality fan that draws 25 L/s (50 cfm). A poor-quality fan won’t exhaust enough air and will be too noisy for regular use. The best fans have sound ratings of 0.5 sones or less and consume about 20 watts. Older units typically run up to 4 sones and 80 watts.
Large bathrooms, or those with bigger fixtures, such as spas, need larger fans. Place the bathroom fan as close as possible to the source of moisture or odor. For in-line fans, as long as the intake grille is properly located, the fan itself does not have to be close to the bathroom. Some bathroom fans have lights or heating lamps. If you choose a fan with integrated lights, look for efficiency. Any fan installed in an insulated ceiling — for instance, if the attic is above the bathroom ceiling — must not leak air and must be rated for use under insulation inflatable sumo wrestling suits.
Make sure that exhaust fans, lights and heaters in bath or shower enclosures are rated and approved for wet conditions. Newer units approved for wet conditions may include ground fault protection.