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I had a call from a customer yesterday that was confused about the size of air cleaner to buy for her room.
Its easy to be confused when it comes to air cleaners. The manufacturer’s pile onto the confusion with talk of square footage and CADR.
It is hard enough to determine what make of machine, then you have to determine what model? So how do you know if you picked the best air cleaner for your room size?
Follow these simple steps to figure out the right size air cleaner.
Well, knowing the square footage of the area is a start. Because we live in 3 dimensions (length, width, and height) you do have to factor in the height of the ceiling. This will give you the volume of the air in the room to be cleaned.
So, Length x Width x Height = cubic feet of air to be cleaned in the room (anyone remember volume from geometry class?)
Next, look at the technical specifications for the machine and find the amount of air moved by the motor. It will be expressed as a number with the letters “cfm” behind it. That means the volume of air the machine can filter expressed in cubic feet of air per minute.
To determine air exchanges, take the volume of air in the room and divide it by the cfm of the machine. That will tell you how long it will take to get one air exchange. Or, in other words, how long will it take for that machine to move all the air in the room through the filter once.
To determine the air exchanges per hour, divide 60 (the minutes in an hour) by the number of minutes for one exchange. You want a number at least 6. 10 is great and more than 10 is more than great!
For example: If you have a master bedroom that is 14 x 14 with 10″ ceilings, and you are looking at an Austin Air HealthMate Regular HM400 air cleaner.
Your calculation would be:
L 12' x W 14' x H 10' = 1,680 cubic feet of air to be cleaned
Austin Air HealthMate has a motor that moves 400 cfm on high
1,680 / 400 = 4.20 minutes for one exchange
60 minutes / 4.20 minutes = 14.29 air exchanges an hour
With those room dimensions, the HealthMate would be a great size for the room!
Lets try that same room with a HealthMate Junior HM 200 and see the difference….
L 12' x W 14' x H 10' = 1,680 cubic feet of air to be cleaned
Austin Air HealthMate Jr moves 200 cfm on high
1,680 / 200 = 8.4 minutes for one exchange
60 / 8.4 = 7.14 exchanges per hour
With those room dimensions, the HealthMate Junior is pushing the envelope of effectiveness. The better choice is the HealthMate.
Watch what happens when you change the ceiling height from 10″ to 12″.
L 12' x W 14' x H 12' = 2,016 cubic feet of air to be cleaned
2,016 / 400 = 5.05 min for 1 exchange = 11.9 exchanges per hour
the HealthMate Junior can still do the job
2,016 / 200 = 10.08 min = 6 exchanges per hour
the Healthmate Junior is now at the limit on the high speed and cannot be turned down to a lower speed.
The reason this calculation is important is because if you just looked at square footage you would think that a Healthmate Junior would be more than enough to clean a room that is 12' x 14'.
Why, a 12' by 14' room is only 168 square feet and Austin Air says a Junior is good for 750 square feet!