Air Purifiers Sizing Table

AIR CLEANERS SIZING TABLE
for Ambient Air Cleaning

The term "ambient air cleaning", as used on this website, is the process of cleaning all the indoor air in the room or facility where there is an air quality issue. This is in contrast to the term "source capture" which refers to capturing air contaminants at their source of emission before they disperse throughout the room or facility air.

The objective is to provide enough air cleaning capacity so as to clean the air at least as fast, if not faster, than the contaminants are being emitted into the air. In other words, the faster contaminants are emitted into the air, the faster the air needs to be cleaned. This translates into cleaning the air more frequently or more times, each hour. The rule of thumb typically used to match the air cleaning capacity to the air contaminant severity and ensure that the air cleaner(s) do not become overwhelmed by air contaminant emissions is illustrated in the following table.

Air Cleaner Sizing "Rule of Thumb"
Severity of Air Contamination	Typical Environment	Frequency of Air Filtration
Light	Residential	filter all the air 4-6 times each hour
Moderate	Commercial	filter all the air 8 times each hour
Heavy	Industrial	filter all the air 10 times each hour
Critical	Medical Isolation	filter all the air 12 times each hour

The frequency of air filtration is commonly known as air changes per hour (ACH). The level of air cleaning capacity is usually designated in terms of cubic feet of air cleaned per minute (CFM) or delivered¹ CFM. The amount of CFM required from the air cleaning equipment depends on the volume of air to be cleaned in the facility and the ACH required to deal with the air contamination severity.

How to determine total delivered airflow needed
The table below provides an indication of the volume of air to allocate to each air cleaner in order to achieve the desired ACH. For instance, if it is determined that an ACH of 8 facility air filtrations per hour is necessary, and, the volume of air in the facility to be cleaned is 3,750 cubic feet, then the desired amount of filtered airflow from the air cleaning equipment is 500 CFM. Once this CFM number is determined, it is possible to select appropriate equipment to deal with the air quality issues. This CFM number represents the total amount of air cleaning CFM required, not necessarily the amount of CFM for one particular air cleaner. In other words, in the example just given, 500 CFM is needed, but if the air purifier being considered will only provide 250 CFM, then two air purifiers are necessary to provide the required amount of total filtered airflow.

How to determine the area size a single air cleaner will filter
If you have a particular air cleaner in mind and would like to know the size area that it will clean, first determine the delivered airflow in CFM for the air cleaner from it's specifications. This is generally available from the product literature. Scroll down the left column of the following table to the CFM figure closest but less than the delivered airflow of the selected machine. Next, look at the volume of air corresponding to the CFM in the table. Divide the volume by the ceiling height of the room to determine the area in square feet.

Volume of Air per Machine vs. Contamination Levels (60Hz electric)²

Contamination Level:	Lightest	Lighter	Light	Moderate	Heavy	Hospital Isolation	Hospital Operating Room
Recommended ACH:	2 (every 30 minutes)	4 (every 15 minutes)	6 (every 10 minutes)	8 (every 7.5 minutes)	10 (every 6 minutes)	12 (every 5 minutes)	25 (every 2.4 minutes)
Air Cleaner airflow (delivered¹ CFM)	Volume of air (cubic feet) allocated to an individual air cleaner with delivered CFM rating in left column versus desired ACH above. e.g. air cleaner with 500 CFM delivered airflow will clean 3,750 cuft of air 8 times each hour.
100	3,000	1,500	1,000	750	600	500	240
150	4,500	2,250	1,500	1,125	900	750	360
200	6,000	3,000	2,000	1,500	1,200	1,000	480
250	7,500	3,750	2,500	1,875	1,500	1,250	600
300	9,000	4,500	3,000	2,250	1,800	1,500	720
350	10,500	5,250	3,500	2,625	2,100	1,750	840
400	12,000	6,000	4,000	3,000	2,400	2,000	960
450	13,500	6,750	4,500	3,375	2,700	2,250	1,080
500	15,000	7,500	5,000	3,750	3,000	2,500	1,200
550	16,500	8,250	5,500	4,125	3,300	2,750	1,320
600	18,000	9,000	6,000	4,500	3,600	3,000	1,440
650	19,500	9,750	6,500	4,875	3,900	3,250	1,560
700	21,000	10,500	7,000	5,250	4,200	3,500	1,680
750	22,500	11,250	7,500	5,625	4,500	3,750	1,800
800	24,000	12,000	8,000	6,000	4,800	4,000	1,920
850	25,500	12,750	8,500	6,375	5,100	4,250	2,040
900	27,000	13,500	9,000	6,750	5,400	4,500	2,160
950	28,500	14,250	9,500	7,125	5,700	4,750	2,280
1,000	30,000	15,000	10,000	7,500	6,000	5,000	2,400
1,100	33,000	16,500	11,000	8,250	6,600	5,500	2,640
1,200	36,000	18,000	12,000	9,000	7,200	6,000	2,880
1,300	39,000	19,500	13,000	9,750	7,800	6,500	3,120
1,400	42,000	21,000	14,000	10,500	8,400	7,000	3,360
1,500	45,000	22,500	15,000	11,250	9,000	7,500	3,600
1,600	48,000	24,000	16,000	12,000	9,600	8,000	3,840
1,700	51,000	25,500	17,000	12,750	10,200	8,500	4,080
1,800	54,000	27,000	18,000	13,500	10,800	9,000	4,320
1,900	57,000	28,500	19,000	14,250	11,400	9,500	4,560
2,000	60,000	30,000	20,000	15,000	12,000	10,000	4,800
2,500	75,000	37,500	25,000	18,750	15,000	12,500	6,000
3,000	90,000	45,000	30,000	22,500	18,000	15,000	7,200
3,500	105,000	52,500	35,000	26,250	21,000	17,500	8,400
4,000	120,000	60,000	40,000	30,000	24,000	20,000	9,600
4,500	135,000	67,500	45,000	33,750	27,000	22,500	10,800
5,000	150,000	75,000	50,000	37,500	30,000	25,000	12,000
6,000	180,000	90,000	60,000	45,000	36,000	30,000	14,400
7,000	210,000	105,000	70,000	52,500	42,000	35,000	16,800
8,000	240,000	120,000	80,000	60,000	48,000	40,000	19,200
9,000	270,000	135,000	90,000	67,500	54,000	45,000	21,600
10,000	300,000	150,000	100,000	75,000	60,000	50,000	24,000
15,000	450,000	225,000	150,000	112,500	90,000	75,000	36,000
20,000	600,000	300,000	200,000	150,000	120,000	100,000	48,000
25,000	750,000	375,000	250,000	187,500	150,000	125,000	60,000
30,000	900,000	450,000	300,000	225,000	180,000	150,000	72,000
35,000	1,050,000	525,000	350,000	262,500	210,000	175,000	84,000
40,000	1,200,000	600,000	400,000	300,000	240,000	200,000	96,000
45,000	1,350,000	675,000	450,000	337,500	270,000	225,000	108,000
50,000	1,500,000	750,000	500,000	375,000	300,000	250,000	120,000

Notes:

IMPORTANT WARNING: Delivered CFM is the rate of air flow through the air cleaner with all filters installed. Beware, some manufacturers cite 'free flow' CFM or CFM '@0"wg', which refer to the performance of the motor and blower combination only, without any air resistance due to the filters. Although we only use delivered airflow values, with other vendors, you should always confirm that the figures are delivered and not free flow as nothing should be left to chance.

Figures based on 60Hz electricity. If 50Hz electricity is used to operate air cleaner, reduce CFM and Volumes by 20%.

The above table was developed using formulas here.

AIR CLEANERS SIZING TABLE for Ambient Air Cleaning

AIR CLEANERS SIZING TABLE
for Ambient Air Cleaning