What is a good cfm for a bathroom ceiling fan?

For most bathrooms this works out to one CFM per square foot of bathroom area. For example, a 7′ x 10′ bathroom would require a 70 CFM fan. A 50 CFM rating is recommended as a minimum for bathrooms 50 sq. ft.

Can a bathroom exhaust fan have too much cfm?

The bigger the bathroom, the higher the CFM rating you’ll need. A fan should have a CFM rating high enough to replace the air in your bathroom at a rate of eight times per hour.

What cfm rating is recommended for a bath fan in a 90 sq ft room?

Bathroom Fan CFM Chart

Bathroom Size (Sq Ft): Required CFM:
70 sq ft 75 CFM
80 sq ft 85 CFM
90 sq ft 96 CFM
100 sq ft 107 CFM

Is 110 cfm good for a bathroom fan?

We recommend at least an 80 CFM for most bathrooms but a 100/110 for a larger master bathroom. This will help move the moisture out of the bathroom and reduce the risk of mold.

How do I know what size exhaust fan I need?


  1. Area of the Room=Length x Width x Height.
  2. Area of the Room=10 x 15 x 10 =1500 Cub. Foot.
  3. From the table Air Changing Rate (ACH) for Bathroom = 8 Times/Hour.
  4. Size of Ventilation Fan = (Area of Room x ACH ) / 60.
  5. Size of Ventilation Fan = (1500 x 8 ) / 60 = 200 CFM.
  6. Size of Ventilation Fan = 200 CFM.

Is it good to oversize a bathroom exhaust fan?

First, it’s a good idea to oversize the fan slightly. In our sample 54-square-foot, for example, it’s a good idea to install a 60 CFM fan for good measure. Second, if your bathroom has a jetted tub or separate rooms or alcoves, you might want more than one fan.

Why are bathroom fans so weak?

The Dampers Are Stuck There are two dampers for a bath fan, one at the housing and another where the duct exits the building. If they don’t open easily or open only partly, airflow will be weak. Try moving the exterior damper by hand to make sure it opens easily. Clean away any debris that might hinder movement.

How many CFM do I need per square foot?

One cfm
One cfm is needed per square foot (1 cfm/sq ft) of floor area. This is the average air quantity required for a room or an entire building. This number is based upon an averaged heat load calculation for comfort cooling.

How do you calculate CFM for a ceiling fan?

CFM measurements are taken when a fan is on high speed, then that number is divided by the watts used. This means that the higher the CFM, the more efficient the fan, and the more air it moves. 75 cfm/w is the minimum to be considered efficient, according to Energy Star requirements.

How do I calculate CFM for exhaust fan?

How to Determine CFM Size for a Bathroom Exhaust Fan

  1. IMPORTANT: An extractor fan MUST be routed to the exterior of your home.
  2. (10ft * 10ft* 8ft)/7.5 = 106.67 CFM.
  3. Cubic Volume/7.5= CFM Necessary.
  4. Bathroom Moisture and Humidity Related: