Calculations are based on homes with 8 ft ceilings. Formula: ACH = CFM of unit x 60 (minutes in an hour) divided by the area of room divided by the room height
The above sizing chart is a guideline only.
Although there is no exact sizing formula for HEPA filters, you should keep a few points in mind.
Generally speaking, the more air changes per hour (ACH) you can have, the more effective a HEPA filter can be.
There are no guidelines as to how many ACH you should provide, but as a rule of thumb, 1 ACH provides excellent air cleaning results. However, you can also get very good results at .5 ACH depending on your preferences, house, etc. As a matter of fact, a HEPA filter performing at .5 ACH will produce better results than most other air cleaning devices on the market. This is important to know, because often budget plays an important role when purchasing a HEPA filter.
People with sensitivities (allergies/asthma) may require an ACH of 2 or higher
Remember: More HEPA is better than less, but some HEPA is better than nothing at all.
