The capacity of exhaust fans is rated in Cubic Feet per Minute (CFM). 50 CFM is the normal rate that a normal bathroom size would need in a good exhaust fan. If what you got is less than that, then it will not exhaust enough air and will become too noisy for regular use.
The best fans would have sound ratings of 0.5 sones or less and would consume about 20 watts. The older types used to run up to 4 sones and 80 watts – too noisy and not energy efficient.
Bathrooms of a larger area and with bigger fixtures, like the spas, would naturally need larger fans. This must be installed as near as possible the source of moisture or odor. In-line fans though do not need to be close to the bathroom as long as the grill is located properly.
Some bathroom ceiling or exhaust fans have their own lights or heating lamps. If you chose one with lights, look for efficiency.
If a bathroom exhaust fan is installed in a ceiling that is insulated – if for instance, the bathroom is situated underneath the attic – air should not leak and since it is for use under insulation, should therefore be rated.
Ensure that the exhaust fans, lights, and heaters above the bath or shower area are approved for wet conditions and high levels of moisture. There are newer models that are already rated and approved for such conditions and may include ground fault protection.
Noise
Most people would not use a noisy fan. Select one that is labeled ‘quiet’ and ‘low noise’ and in the size that you need.
Check for HVI rating or the Home Ventilation Institute rating. If the product has no such rating then most likely it would be a noisy fan.
Airflows and Fan Power Requirements
The quality of your ducting can affect performance of your bathroom exhaust fan.
If your duct is uninsulated, droopy flex, or undersized, dirty and ineffective exhaust louvers and back draft dampers can cut the airflow by as much as over fifty percent.
To test if your fan is drawing air, hold a piece of toilet tissue paper up to the grille. The exhaust air should suck the tissue and hold it tight onto the grill.
Check also the outlet to ensure that the air is leaving your house.
Controls
Most installations of bathroom exhaust fans are connected to light switches therefore, they start running when you turn the light on. However, often enough, the light is switched off after a shower or bath, and the moisture had not been effectively exhausted totally. It is recommended therefore to separate the switch of the fan and the lights, which is common enough.
Although there are other ways such as getting fans that have humidity or motion sensors that can automatically turn on or off when either or both have been detected in the bathroom. These type of fans have settings that you can control, specifying maximum levels of humidity.
You may also use an exhaust fan that has a delayed shut-off system that keeps on running up to 15 minutes more after you leave the bathroom.
Cleaning
All types of fans create static electricity that attracts dirt to the fan and its housing like a magnet. This then would encourage growth of mold and would restrict air movement. Therefore, you must ensure regular cleaning is done. Check your product’s manual on the proper care and maintenance.
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