Bathroom Fan Duct Size

The larger the duct diameter the greater the airflow.

Bathroom fan duct size. Can i add another fan in line to improve air flow or will one fan work against the other. Virtually all fans provide more airflow with less noise when the duct is up sized an inch or two when smooth duct is used and when duct runs are as straight as possible. Required bathroom vent fan ventilation rate in cfm this ventilation code specifies a bathroom exhaust airflow rate for toilet rooms and bathrooms not served by a window of adequate size of 25 or 50 cfm ft for hotels motels resorts and dormitories and a slightly more modest 20 50 cfm for private dwellings. In order to make the vent fan as quiet as possible mount the fan itself as far as possible from the intake register in the bathroom.

To determine the square footage of your bathroom multiply the length times the width. For example if your bathroom is 6 feet wide and 9 feet long its square footage is 54. Check the size of the exhaust port on the fan to make sure it fits your ductwork if applicable. 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 exhaust to disperse outdoors. Replace 3 duct with 4 or 6 duct. I installed a 5 duct fan for bathroom exhaust the total length of duct to outside is less than 6 ft. Actual results may vary based on differences in equipment materials and installation.

Assumptions are consistent with these tables i e 15 for elbows 30 for a termination fitting standard temperature and pressure and roughness factors of 0 0055 for flex ducts and 0 00038 for smooth ducts. The fan won t even push the damper open even with the spring on the exhaust damper removed. A bathroom fan may be listed for installation over bathtubs and showers when connected. The basics of venting a bathroom exhaust fan.

The company does not cite a maximum exhaust duct length. The duct fan is rated 120 cfm free air. Fantech recommends a minimum of eight feet of insulated flex duct between the exhaust inlet register or grille and the fan motor. Standard fan sizing applies to bathrooms that are 100 square feet or less.

Often included with the fan to fit the smaller duct.