Bathroom exhaust fan duct size. I have a bathroom that is 8 x 45 and walls are 8 tall so a total volume of 288 CF. I have an old run of nearly 20 of 3. This page is designed to be a general guide for selecting an exhaust fan based on the size of the room and the type of application the fan will be used for. Most bathroom fans are available in four-inch 4 and six-inch 6 diameters. 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. For a standard 10ft by 10 ft bathroom with an 8 ft ceiling you will need an exhaust fan capable of 10667 CFM. They are installed on the ceiling of the room. 4 or 6 Duct for Bathroom Fan.
Install the exhaust fan properly. I have a bathroom that is 8 x 45 and walls are 8 tall so a total volume of 288 CF. Small bathrooms can get by with smaller fans utilizing a smaller pipe but larger fans will need bigger pipes. Heres a table indicating the different sizes of fans and the pipe that should accommodate each one.
If you prefer to use flexible duct an easy way to make it comparable to a metal duct is to oversize it. I have an old run of nearly 20 of 3. But searching the web also lead me to IRC table M15062 Duct Length which I understand to say that a higher CFM also needs a larger duct. Dont make the opening too big as this will hinder the process of insulation. The formula to calculate bathroom exhaust fan size reads as follows.
The rules of the building code apply to duct fans as well. The length of duct that can be used depends on the fan and the duct diameter and whether the duct is flexiblewith corrugated inner surface or hard. Install the exhaust fan properly. While there is no single Right Answer to allowable duct length without considering a number of parameters as youll read below a 3-inch diameter exhaust duct for a bath vent fan is not going to work for you nor anybody else unless your design accepts a 50 cuft CFM and a maximum length of five feet. LARGE MAKE-up ATRExFIAusT F DESIGN CONSIDERATIONS. I need to run a length of 20 feet from that location to the soffit. Below for sizing smooth duct.