A bathroom must have adequate ventilation to prevent the buildup of moisture, mildew and odors. A window alone may be inadequate and certainly will not move the volume of air that a proper-sized fan will.

Some building codes require that a bathroom contain either a window that is openable or an exhaust fan, but not both. It is a good idea to have both, however, since a window frequently remains closed in cold weather.

Exhaust fans are rated according to the cubic feet of air moved per minute (CFM). The Home Ventilation Institute suggests the following formula to determine the size of the fan required for a bathroom (assuming an 8' ceiling): Multiply the length of the bathroom by its width, then multiply that number by 1.1, and you have the minimum size fan suggested for the space. For example, a 5' x 9' room would be 45 square feet. 45 x 1.1 = 49.5 or a minimum of 50 cfm exhaust fan. In addition to the basic ventilation fan, there are fans that come with lights and fan-forced radiant heaters. The heat-fan-light combination can pay for itself in less than a year, based on the amount of energy that is saved in heating the entire home just to get the bathroom warm enough for showering on cold winter mornings.

Ventilation fans have become such a popular do-it-yourself project that most of the products are packaged with non-technical and user-friendly installation instructions. Some manufacturers have even gone so far as to include toll-free consumer hotlines to assist do-it-yourselfers with installation questions.

Exhaust fans, fan-lights, and heat-fan-lights are installed in basically the same way, with the two latter units requiring a little more electrical work.

To be most effective, the fan housing should be attached to the framing at the highest point in the ceiling. All fans should be exhausted through the exterior, not into the attic, via a flexible aluminum or plastic tube that originates at the fan housing and terminates at a roof jack or termination cap that is attached to the roof. This tubing should be attached at both ends with two sheetmetal screws. The connections should also be wrapped with silver duct tape for a virtually airtight fit.

Because this task involves electrical and mechanical work, it may be a good idea to ask local building officials if a permit is required.