Bathroom Fan Duct Length

If your bathroom is larger than 100 square feet tally the cfm requirements for the individual fixtures to estimate your needs.

Bathroom fan duct length.

The photo shows a few examples of what we call equivalent duct lengths how long a duct appears to the fan motor. All municipalities have different requirements but some do not draw a hard line on requiring exhaust fans. For example if your bathroom is 6 feet wide and 9 feet long its square footage is 54. Bathroom and 70 ft.

Or greater or by mechanical means a bathroom vent fan 20 continuous or 50 cfm intermittent vented to the building exterior. To do this you can use a chart like this. A 50 square foot or smaller bathroom needs a 50 cfm fan. Every little roughness on the inside of the duct makes it harder to get air to flow so flex duct with ridges on the inside is twice as long as smooth ridged ducting at.

Therefore it should have a fan rated for at least 54 cfm. For bathrooms between 50 and 100 square feet estimate approximately 1 cfm per square foot. The basics of venting a bathroom exhaust fan. In general for rooms with 8 foot ceilings.

Once you ve got all the information it s time to select an appropriately sized fan. Maximum recommended length of straight duct in compliance with 2015 irc section m1506 2 and 2018 irc section m1504 2 ft 172 ft 331 static pressure in w g air flow cfm 0 100 200 300 400 500 600 700 800 0 0 2 0 4 0 6 0 8 1 design conditions. As an aside my roof has gable vents but does not have soffit vents. The rule of thumb is that you need at least 1 cfm per square foot of room area.

This would be fairly straightforward. The only problem is that the duct length would be 20 25 feet. 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. Fantech recommends a minimum of eight feet of insulated flex duct between the exhaust inlet register or grille and the fan motor.

600 cfm 0 37 in w g. To determine the square footage of your bathroom multiply the length times the width. 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. What is the maximum duct length from a bathroom fan.

The company does not cite a maximum exhaust duct length. The bath is 770 cubic feet 8 12 8 and the fan is a nutone rated at 130cfm if that makes a difference. Using this chart you ll find that for a 640 cu. Surprisingly bathroom fans are not required by some building codes.

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.