Bathroom Insulation and Ventilation
Determine Air Exchange Per Hour [ACH’s]
Air exchanges per hour means an air flow rate sufficient to remove the air volume in a given room at a specified number of times each hour.
Your bathroom exhaust fan should be sized properly to have completely change out the air in the bathroom 11-15 changes in one hour. This is needed in order to remove the moisture while showering and to clear the air after showering.
Locate your bathroom fan to ensure maximum most air extraction. Steam rises so the shower ceiling is always a good spot for a shower fan.
Air removed from a bathroom should be replaced with dry air drawn from an adjacent room or hallway. Replacement air or “make-up air,” is the amount of air that needs to enter the bathroom in order for the fan to work effectively. This air typically enters under a doorway or window.
I typically locate the fan in the ceiling of the shower or right outside the shower, in the ceiling.
Bath fan ducting can negatively affect fan performance. Uninsulated, undersized, or droopy flex ducting, excessive length or elbows all affect and can restrict the fans rated airflow. In order to keep the fan effective try to layout your installation with minimal turns. One thing that people do not realize is that ninety degree elbows in your duct run is like adding 10-15 feet of air flow resistance.
The best duct pipe to use is solid smooth aluminum. Solid duct pipe has a better airflow due to its low-resistance (smooth) exhaust ducting.
When installing, seal the joints, install seams facing upward, and insulate sections that run through any unheated crawl spaces or attic spaces.
Tip: All fans come with instructions that instruct you how far a run your duct work can be – be sure to follow these duct run recommendations or get a higher CFM fan.