As many of you who have shopped or browsed our site have seen, there's a section on each product page where we field your specific questions about products. All are answered and many posted back to the website to help others. One question that has popped up several times in the last two weeks is about air exchanges per hour (ACH) and coverage area. I'll go over it a bit here, and if you want more detailed information, provide a link to a more in depth piece about ACH, below.

_Two readers astutely pointed out a discrepancy between what Austin Air states as their coverage area for the HealthMate air purifier and what we state. Austin lists the HealthMate with 1500 sq. ft. of coverage, while we say it covers 750 sq. ft. Who's correct? Technically, both.

_Coverage area is determined by a couple things. First, how powerful the fan is. The more powerful the fan, the larger volume of air it can move and ultimately clean. The second is how you actually define coverage. Air purifiers aren't like paint. With paint you're going to get about x number of sq. ft. out of each can. This number can vary a little depending on how heavy you apply, but generally, if four people paint with the same bucket, they're going to get pretty similar coverage areas. With an air purifier, the coverage not only describes how large of a room/space it will operate in but also sheds some light on how well it will actually clean in that size of space.

It's wise to remember how an air purifier works. Air moves through the filters, pulled in by the fan, and once cleaned, it's pushed back into the room. This process happens over and over, and for good reason. Air is constantly being polluted with indoor and outdoor allergens and particles. The ACH is the measure of how often an air purifier can cycle through the entire volume of air in any space, and this is linked to how powerful the fan is. If you have a very powerful fan and the air purifier is operating in a small room, it's going to have the ability to cycle through all the air in that room many times per hour. If you take that same air purifier and place it in a large cavernous room, it may only be able to cycle through that volume of air once or twice per hour.

So in large part, coverage area depends on how many air exchanges per hour you want to target. We generally recommend a minimum of four ACH per hour, and that's true for every air purifier we sell. That's the minimum though, and if possible, we recommend getting to six per hour. Air purifier manufacturers vary when it comes to ACH. Some rate the coverage of their machines based on 5 or 4 ACH and some, like Austin, base it on 2 ACH. This means, that Austin Air Purifiers will appear to have very large coverage areas, when it reality if your goal is to filter all the air in your room at least 4 times per hour, then the space can be no bigger than 750 sq. ft. If someone else only needs light filtration, say 2 ACH, over a larger area, then perhaps the Austin HealthMate is perfect for a 1500 sq. ft. area.

As you can see, coverage and ACH are closely linked, and as I've shown here, when it comes to who's right – Austin or us? Both.

For more information on how to calculate air exchanges per hour or visit our highly informative Air Purifier Buying Guide for all the info you need to make the most informed choice about which HEPA air purifier is right for you.

Author: K. Gilmore