Bathroom Insulation and Ventilation

By Robert Robillard on Bathrooms

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.

Fan Location

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.

Bathroom Ventilation and InsulationDetermining Fan Duct Length – How Long?

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.

Bathroom fan


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About the author

Robert Robillard

Carpenter / Remodeler / Editor

Rob Robillard is “The Concord Carpenter” Rob is a builder, general contractor, carpenter, woodworker, and editor of Concord Carpenter and ToolBoxBuzz As a General Contractor and carpenter, Rob owns and operates Concord Carpenter LLC. A full-service remodeling and construction company. Rob is a recognized leader in home building best practices and a source for how-to information for building professionals. On this website, Rob covers all aspects of home construction, building science, home improvement, woodworking, remodeling, and some of the best product and tool reviews. Rob is in charge of our Tool and Product Review series - Concord Carpenter Videos where we post all of our tool reviews and video tutorials. Rob approaches remodeling and building construction with a pragmatic and problem-solving approach. He enjoys using his knowledge and experience to help and educate building professionals as well as DIYers on best practices in the construction and remodeling industry. He's a strong advocate for "raising the bar" in the construction trades and promoting the trades to youth. #BeAMentor #Green2Great Craftsmanship, quality, and pride guide his journey on this channel The Concord Carpenter's motto: "Well done is better than well said!" : Read more about Rob

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