Bath Fan Duct Size

Learning how to calculate cfm for a bathroom fan will help you purchase the right size fan for your space.

Bath fan duct size.

Check the size of the exhaust port on the fan to make sure it fits your ductwork if applicable. All exhaust fan companies have a chart or equations to calculate the minimum exhaust fan sizing per room size width x length x height for cubic feet. A diameter of 4 inches is common for exhaust ducts but some high cfm fans fit a 6 inch diameter duct. I installed a 5 duct fan for bathroom exhaust the total length of duct to outside is less than 6 ft.

They are very. Smooth rigid duct delivers better airflow than metal flex duct. A 3 or 4 inch duct connects to the outlet on the fan housing and runs to a side wall or to the roof and connects to a vent cap that allows the. The larger the duct diameter the greater the airflow.

The duct fan is rated 120 cfm free air. Replace 3 duct with 4 or 6 duct. To be effective a bathroom fan needs to be powerful enough to completely replace the air in the room about 8 times every hour. Result maximum recommended length of straight duct in compliance with 2015 irc section m1506 2 and 2018 irc section m1504 2 ft 0 ft nl no limit on duct length for the specified system.

The bathroom exhaust ventilation fan disperses air through an opening in the fan housing which is usually 3 inches in diameter and ideally faces in the direction of the ventilation system outlet. The effectiveness of the fan will be rated in cfm or cubic feet per minute of air moved. Duct sizing is pretty much what the size of the fan exhaust fitting is. Chad certainly a manufacturer s instructions are most important to follow.

I d like to have a copy of that manual for review and to see the manufacturer and the age of the product and its information. Often included with the fan to fit the smaller duct. The fan won t even push the damper open even with the spring on the exhaust damper removed. The minimum allowed fan size is 50 cfm so if your bathroom is for example only 42 square feet you still need a 50 cfm fan.

A bathroom fan may be listed for installation over bathtubs and showers when connected. On 2020 06 20 by mod follow the manufacturer s specs on bath exaust fan duct size length limits.