This >catskill houseblogger faced a problem that many homeowners with older homes must deal with and that is proper bathroom ventilation. His bathroom is located in the middle of the home which makes this problem a bit more complicated but his installation went smoothly and it all started with determining the proper CFM (cubic foot per minute) for his bathroom size.
The basic standard for a bathroom ventilation fan is it must be able to change the room air 8 times in an hour. To calculate that is pretty easy if you have bathrooms with 8 foot ceilings. Basically it is 1 Cubic Foot per Minute (CFM) for every 1 square foot of floor space, so if you have a bathroom that is 10 ft by 10 ft (or 100 square feet) a 100 CFM ventilation fan is needed. For bathrooms larger that 100 square feet, the ventilation rate depends on the number and type of fixtures in the bathroom.
Some How-To’s for bathroom fan installation
Decorative Fan Choices