Q. My husband and I are in the process of remodeling our bathroom. Can you give us some info about installing a bathroom fan?

A. In my book Ed Del Grande's House Call, I have a complete section on "Bathroom Exhaust Fans." Here is an excerpt:

The old expression "In with the good air, out with the bad air" applies when you're trying to save someone's life. Unfortunately, some people don't understand how important this concept is when it comes to the life of the bathroom.

With all those plumbing fixtures packed into a small space, most bathrooms will inevitably be very moist areas. To my dismay, many homeowners and their family members never use the exhaust fan for their bathroom unless it's wired directly in with the main bathroom light switch. I bet some of you believe that you are using your exhaust fans properly, and think the fan is just meant for eliminating bathroom odors when company is over.

While your bathroom fan does help control normal odors, the real reason for an exhaust fan in your bathroom is to control the moisture. Odors, although embarrassing, will not normally damage your bathroom. Moisture, on the other hand, can cause a lot of problems for any bathroom. Fresh-air intake for a bathroom is key to avoiding moisture-related problems like mold, mildew and material damage.

Ideally, you should use the fan every time you enter your bathroom and leave it on for at least 20 minutes after you use any fixture. (This is why many contractors wire the fan and lights separately.) Now how many of you are actually using your bathroom exhaust fans properly? Once you realize the importance of good bathroom ventilation, the first bathroom project you should take on is to inspect all the components of the existing or proposed exhaust fan, for proper operation and ventilation.

If you're inspecting your bathroom's present ventilating system or installing a new system from scratch, there are guidelines you need to follow to ensure proper ventilation. Think of your bathroom venting system as a chain. If one of the links does not do its job, the entire system will fail. The three main links in the venting chain are:

1. Adequate fresh-air intake. To move moist air out, you must have a large enough intake opening to get fresh air into the bathroom. The easiest way to do this is to make sure you have a gap of at least a half inch under your bathroom door.

2. Proper exhaust venting. The exhaust duct should have smooth internal surfaces with few bends and a short run for the best airflow. The duct has to be vented to the outside of the home with a dryer-type hood and flap to prevent back drafts.

3. Appropriate CFM motor size. The bathroom size will determine the "cubic feet per minute" rating of the fan. For instance, an 8-by-8-foot bathroom should use a fan rated around 102 CFMs to supply the recommended 12 air changes an hour.

Visit www.EdDelGrande.com or e-mail EdDelGrande@hgtvpro.com.