As the trend to larger spa-like bathrooms continues to gain in popularity, the need for proper ventilation becomes more important.  While many people are tired of their noisy and in effective bath fan - not many people know how to properly size a fan to their needs.


There are a few different ways to calculate 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.

METHOD 1

This method works on the assumption that the goal for bathroom ventilation is 8 complete air changes per hour.  Take your square footage x ceiling height to get the total cubic feet to be ventilated.

Example:  Bathroom measures 10 feet wide and 12 feet long.  It has 8 foot ceilings.  So 10 x 12 x 8 = 960 cubic feet.

We take the cubic feet and divide by 60  - which is the number of minutes in an hour.  We take the result and multiply by 8 (remember, our target is 8 complete air changes each hour).  The complete equation is as follows:



STEP 1
10 ft X 12 ft X 8 ft = 960 cubic feet.

STEP 2
960 divided by 60 = 16.

STEP 3
16 x 8 = 128

So - we need 128 CFM of air movement to properly ventilate this bathroom.  Assuming there is not and excessively long or twisting duct run to the outside - we would select a fan that moves somewhere around 130 CFM or higher.  Examples would be the Panasonic FV-15VQ4 or Broan QTXE150FLT, both of which are rated at 150 CFM.  If an inline fan is desired - the Fantech FR 110 would suffice.


METHOD 2

This method is a simple one - for bathrooms under 100 square feet.  According to guidelines of HVI (Home Ventilating Institute) baths 100 square feet or smaller require one CFM per square foot of bathroom - with a minimum of 50 CFM.

So - if you have a 7 foot by 9 foot bath - you need 63 CFM. It doesn't get any simpler than this.  Most conventional ceiling insert fans, however, are rated either 50 or 80 CFM - so you will have to round up or down (rounding up preferred).


METHOD 3

This method of calculation is designed for bathrooms over 100 square feet and factors in the number of fixtures in the bath (toilets, showers, tubs).  The rules are:

* Allow 50 CFM for each standard toilet, shower or tub
* Whirlpool and jetted tubs need 100 CFM

So - if you have 1 toilet (50 CFM), 1 shower (50 CFM) and 1 whirlpool tub (100 CFM) - you will need a 200 CFM Fan.
Contact us today at 604-536-5672 for more information about your bathroom ventilation fans. We serve the entire Lower Mainland: Vancouver, Burnaby, New Westminster, Richmond, Surrey, White Rock, Langley, Cloverdale, Aldergrove, Coquitlam, Maple Ridge, Mission, Abbotsford.