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Bathroom Exhaust Fan


Installed correctly, a bathroom exhaust fan can be used to remove moisture and odors and also run continuously as a whole-house fresh air system for a healthier indoor environment.

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This U.S. Department of Energy checklist includes important specifications that can contribute to a complete and quality installation. All work shall comply with these specifications, all relevant codes and standards, and all manufacturer installation instructions. The contractor shall check each box on the checklist below and sign and date at the bottom to certify the work is completed.


Bathroom exhaust fans used only for spot exhaust shall have a mechanical exhaust capacity of at least 20 cfm for continuous operation, or at least 50 cfm for intermittent operation. To ensure these minimum flow rates are met, it is recommended that the bathroom exhaust fan selected has a rating of 50 cfm for continuous operation, or 70 cfm for intermittent operation.

Bathroom exhaust fans used for continuous whole-house ventilation shall have a mechanical exhaust capacity based on house size as follows: 50 cfm for up to 1,500 ft², 70 cfm for 1,501 to 2,500 ft², and 100 cfm over 2,500 ft².

The bathroom exhaust fan shall be ENERGY STAR certified.

If connecting the new fan to an existing exhaust duct, the existing duct shall be checked to ensure it is made of rigid metal (e.g., galvanized steel, stainless steel, or copper), has a smooth interior surface, is equipped with a functioning back-draft damper, meets the maximum length guidelines specified in the IRC (2015 IRC Table M1506.2), and meets the minimum diameter or dimension guidelines specified in the fan manufacturer’s installation instructions. If not, the homeowner shall be advised to replace the exhaust duct.

The bathroom exhaust fan shall be installed to vent outdoors, not into an attic, crawlspace, or space between floors.

The exhaust duct shall be installed with the most direct route to the outside, with as few bends as possible, and with no bends for the first three feet of duct from the fan.

The exhaust duct outlet vent shall be located on the exterior of the home at least 10 feet from any air inlet and where it does not direct air flow onto a walkway.

All exhaust duct seams and connections shall be sealed with mastic or UL 181 tape.

All ceiling and wall or roof penetrations shall be sealed with mastic, caulk, or spray foam at interior surfaces and flashed at exterior surfaces.

In a vented attic, the exhaust fan housing should be covered with an airtight box made of rigid foam or another solid material. The box should be air sealed to the ceiling drywall with caulk, spray foam, or tape. The box and the duct shall be covered with attic insulation.

The wall cap shall include a damper that closes when the fan is not exhausting.

The wall cap damper shall be checked to ensure it is operating correctly.

The exhaust fan flow rate shall be measured using a flow hood, flow grid, or anemometer, in accordance with the test procedures listed in ANSI/RESNET/ICC 380-2016 and adjustments shall be made to ensure the fan is providing the minimum flow rates specified above.

The fan should be set to operate as desired by the homeowner (e.g., spot or continuous ventilation) and maintenance procedures shall be reviewed with the homeowner (e.g., check vent annually and clear debris and insect nests).

A radon test kit shall be provided to the homeowner with a recommendation to remediate if post-retrofit radon is above EPA limits.

Bathroom Exhaust Fan Background

Bathroom Exhaust Fan

Washing and bathing release significant amounts of water vapor into the air. For instance, a shower produces a half pint of water vapor for every 5 minutes of run time. With no exhaust fan, this moisture can accumulate and increase the risk of mold and mildew on floors, walls, and ceilings. High-efficiency exhaust fans can quietly exhaust bathroom air to the outside. These bathroom exhaust fans can be operated manually or automatically with humidity sensors. In addition, they can be operated continuously as a whole-house fresh air system to exhaust stale air. Make-up fresh air supply relies on natural infiltration air flow through the holes and cracks in home construction.

Tips to Sell Quality Installed Home Improvements

Home Improvement Expert is a valuable tool for organizations committed to quality installed work. The following tips help optimize the value of this tool when selling home improvements:

Trust Matters: Inform homeowners how your work conforms to this world-class expert guidance. Recommend they visit the DOE website as evidence these are indeed official best practices.

Knowledge Matters: Take advantage of the Building America Solution Center as a resource for becoming an expert on these projects.

Clarity Matters: Tell prospective clients to contrast your expert-recommended best practices with other contractors.

Value Matters: Advise prospective clients to insist other bids also include these checklists to ensure equivalent quality work.

Message Matters: Showcase on your website and marketing materials that your company uses the highest quality best practices specified on HIE Checklists.

Experiences Matter: Provide visual evidence contrasting the difference between poor and high quality work such as infrared images; pre- and post-energy bills; short and long warranties; and simple charts and graphics depicting performance advantages.

BASC Guides

Guide describing how to install a bathroom fan to remove excess moisture, cleaning chemical fumes, etc.
Guide describing the bathroom exhaust fan ENERGY STAR rating requirements.