Standard Duct Size For Bathroom Exhaust Fan

A bath vent fan duct that is too long may restrict air flow such that the fan is not functional.

Standard duct size for bathroom exhaust fan.

Here we provide specifications for recommended minimum maximum duct lengths for bathroom vent fans. Bathroom vent fans are rated by the cubic feet per minute cfm of air they move and should be sized to replace the air in the room at least eight times an hour. For a standard 10ft by 10 ft bathroom with an 8 ft ceiling you will need an exhaust fan capable of 106 67 cfm. The rule of thumb is that you need at least 1 cfm per square foot of room area.

Cubic volume 7 5 cfm necessary. A diameter of 4 inches is common for exhaust ducts but some high cfm fans fit a 6 inch diameter duct. Bathroom exhaust fan duct length specifications. The fan pulls air out of the bathroom and allows fresh air to be drawn in.

A bath vent fan duct that is too short may violate the manufacturer s installation instructions may not work properly or may be drafty. Bathroom vent fans are rated for the amount of air they can move measured in cubic feet per minute or cfm. Standard fan sizing. The duct fan is rated 120 cfm free air.

A 0 to 400 cfm fan requires a 4 inch minimum duct size but a 6 inch duct is recommended. The formula to calculate bathroom exhaust fan size reads as follows. Standard fan sizing applies to bathrooms that are 100 square feet or less. The minimum duct sizes and recommended duct sizes based on a hood fan s cfm rating are as follows.

Bathroom fan exhaust size calculator. The fan won t even push the damper open even with the spring on the exhaust damper removed. Here s how we get this number. Ft in the room.

If your bathroom has an 8 ceiling the cfm rating for your fan should be as least as high as the number of square feet 5 x 7 35 sq. 10ft 10ft 8ft 7 5 106 67 cfm. A large bathroom with a jetted tub a toilet and a shower a common configuration in new homes would need a 200 cfm ventilation fan such as the broan l200 ventilation fan available from. Check the size of the exhaust port on the fan to make sure it fits your ductwork if applicable.