Bathroom Fan Duct Length

All municipalities have different requirements but some do not draw a hard line on requiring exhaust fans.

Bathroom fan duct length.

The basics of venting a bathroom exhaust fan. 600 cfm 0 37 in w g. Or greater or by mechanical means a bathroom vent fan 20 continuous or 50 cfm intermittent vented to the building exterior. Surprisingly bathroom fans are not required by some building codes.

The rule of thumb is that you need at least 1 cfm per square foot of room area. What is the maximum duct length from a bathroom fan. Therefore it should have a fan rated for at least 54 cfm. To determine the square footage of your bathroom multiply the length times the width.

Bathroom code does address the issue of moving odor and moisture laden air from the bathroom to the outside. Fantech recommends a minimum of eight feet of insulated flex duct between the exhaust inlet register or grille and the fan motor. This would be fairly straightforward. The bath is 770 cubic feet 8 12 8 and the fan is a nutone rated at 130cfm if that makes a difference.

Of duct equivalent length you ll need a 110 cfm fan to achive the recommended 8 air changes per hour. In general for rooms with 8 foot ceilings. Once you ve got all the information it s time to select an appropriately sized fan. 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.

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. Bathroom and 70 ft. 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. Using this chart you ll find that for a 640 cu.

For bathrooms between 50 and 100 square feet estimate approximately 1 cfm per square foot. To do this you can use a chart like this. The only problem is that the duct length would be 20 25 feet. As an aside my roof has gable vents but does not have soffit vents.

The photo shows a few examples of what we call equivalent duct lengths how long a duct appears to the fan motor. A 50 square foot or smaller bathroom needs a 50 cfm fan. The model building codes adopted by most jurisdictions typically require bathroom ventilation to be provided either by an operable window 3 sq. The company does not cite a maximum exhaust duct length.

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