How to figure cfm for a bathroom fan

how to figure cfm for a bathroom fan
In order to interpret exhaust fan airflow, you must measure the fan operating static pressure and the fan speed or Revolutions Per Minute. Determine the required CFM for your bathroom fan.

how to figure cfm for a bathroom fan

While many people are tired of their noisy and innefective bath fan - not many people know how to properly size a fan to their needs. There are a few different ways to calcuate the number of Cubic Feet Per Minute CFM of air movement needed to properly ventilate a bathroom. Make sure you check out the end of the article and read about static pressure. A long duct run from the fan to the outside can skew your calculations.

how to figure cfm for a bathroom fan

Bathroom measures 10 feet wide and 12 feet long. It has 8 foot ceilings. We take the result and multiply by 8 remember, our target is 8 complete air changes each hour.

Is it possible to have too large of a CFM for your bathroom? There really is no harm in changing out more air in your bathroom.

how to figure cfm for a bathroom fan

However, with high CFM usually comes bigger size, noise, and price. The fan may look big in a small bathroom. Another issue is that if you are pushing air out of the house at a high volume, it has to be replaced somehow.

how to figure cfm for a bathroom fan

It will pull air from somewhere else to replace this air, such as reversing the flow of air in your fireplace chimney or your hot water heater vent if its gasor your kitchen island hood. Thus, there can potentially be adverse effects of overventilation. Not Helpful 0 Helpful 5.

Exhaust Fan CFM Calculator

How can you select the proper exhaust fan? Get the CFM of the space where you plan to install an exhaust fan. Not Helpful 4 Helpful 8. Already answered Not a question Bad question Other.

Bathroom Vent Fan CFM Calculator

Tips The measurements you take do not need to be incredibly precise. As long as your numbers are roughly accurate, the fan you choose should be effective.

how to figure cfm for a bathroom fan

For example, if your bathroom is 6 feet wide and 9 feet long, its square footage is Therefore, it should have a fan rated for at least 54 cfm. But before you start shopping, there are a few things to consider.

4 Ways to Measure Airflow

First, it's a good idea to oversize the fan a bit. In the above example, you should get at least 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 see below.

Calculating Cubic Feet

Knowing what size bathroom fan you need is easy to calculate. All you need is a tape measure and a calculator. An extractor fan MUST be routed to the exterior of your home.

Read this to understand why. For a standard 10ft by 10 ft bathroom with an 8 ft ceiling, you will need an exhaust fan capable of Bathroom extractor fans are mandatory in any bathroom without a window and still highly recommended in bathroom with windows.


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