By MATT MAURY

For many of us, every time we take a shower the windows and mirror in the bathroom end up covered with steam. Of course, we have turned on the fan, but the amount of noise does not reflect the efficiency of the suction. After we dry ourselves off, we ineffectively use the towel to wipe the beads of moisture off the mirror. Each time we go through this ritual, we think to ourselves, "Something has to be done about that fan!"

But, before rushing out to buy a new bathroom fan, consider these five factors in making your decision: airflow, noise level, motor life, the operating switch and the exhaust venting.

Airflow is defined in cubic feet per minute (CFM). For bathrooms up to 100 square feet in size, it is generally recommended that an exhaust fan remove 1 CFM per square foot. For example, a 6-foot-by-10-foot bathroom has 60 square feet and requires a fan that is rated to remove 60 CFM. For larger bathrooms, figure 50 CFM per toilet, shower and tub. Since fresh air must replace the exhausted air, be sure that doors or windows can be left open to allow proper airflow into the room.

Noise level has been a universal problem with bathroom fans. Until recently there were no "very quiet" fans on the market. Now, at least four manufacturers offer models that are markedly quieter than those installed in homes more than five years ago. Noise can be measured in "sones." It is not so important to know what a sone is as to know that the measuring scale is exponential. Each number higher on the scale is 10 times greater than the last number. A "2" is 10 times louder than a "1." Inexpensive fans generally have a noise level above 2.5 sones, while the newer (and more expensive) "quiet fans" are rated at 0.5 sones. You can barely hear them running.

Motor life is another important consideration, since it is recommended that a fan be run for at least 15 minutes after a shower or bath. Some fans have an expected motor life of over 30,000 hours. Another aspect of the motor is its energy efficiency. With the cost of power rising, it is wise to consider operating costs. A higher priced, more efficient fan will probably save money in the long run.

The operating switch that turns the fan on and off will be a key to good performance. No longer does one have to listen to the "tick, tick, tick" of a timer winding down above the roar of the fan. New technology has brought about a switch that can be set for times up to an hour, where there is nothing more than a light on the panel showing the amount of time left for the fan to run. This type of switch can replace any existing switch, even if the fan is not replaced.

The exhaust venting carrying the moist bathroom air outside may need to be replaced to assure efficient airflow. Many times the venting is done through flexible tubing that appears to be the type of hose coming from a clothes dryer. With all the ridges and valleys in the tube, the air bumps and jiggles all over before exhausting itself. Think of driving down a cobblestone street rather than a smooth concrete surface. You slow down to avoid being bounced around. The same thing is happening to the air being forced out the venting tube. The air slows down making the fan less efficient. Metal ductwork is always recommended for bathroom fan venting.

The technical information is available from both retailers and manufacturers, often on their Web sites. Some of the more expensive fans are available only through electricians or professional installers. Guess the manufacturers figure that people who want a high quality fan will want it installed by someone who is trained to do it properly. (