Wondering how do you know how many air scrubbers to use in a restoration or mold remediation project? With some simple math and air scrubber calculations you can determine the right number of air scrubbers to use, maximizing both profitability and efficiency. You can save money, too. If you’re picking the right commercial air scrubber, knowing how many you’ll need plays a big role.

## Negative Air Pressure

In order for an air scrubber to remove contaminants from an environment, we need to create negative air pressure. Simply stated, to create negative air pressure more air needs to leave a room than is entering it. That’s the job you’ll rely on the air scrubber for.

Negative air pressure is key to containing dirt, dust, fumes, fungus, mold, smoke and other particles from the environment.

## Air Scrubber CFM (Cubic Feet per Minute)

CFM stands for cubic feet per minute. It is also a standard way of classifying the efficiency or duty cycle of an air scrubber or negative air machine.

## ACPH, or APH (Air Changes per Hour)

A key aspect in remediation and restoration is understanding how many air changes per hour are required to adequately clean the air. Some say, even for mold remediation, four air changes per hour is adequate. Others say more. An industry standard is six air changes per hour, but there are several factors that could warrant increasing or decreasing that number.

## Size of the Building, Room or House in Cubic Feet

In addition to knowing how many air changes are desired, we’ll need to know the size of the area being cleaned. For each room in a home or building, multiply the room length, width and height. When calculating the height, you need only account for the height to the ceiling. This calculation tells us the cubic footage of the room.

*cubic feet = length * width * height *

Tip: Cubic feet and square feet are very different numbers. Make sure your calculations use cubic feet or any air scrubber calculations will be off dramatically!

## Calculate How Many Air Scrubbers you Need for a Job

To arrive at the number of air scrubbers needed for a remediation, restoration or other job, use the following steps:

- We will first calculate the size of the room in cubic feet. The equation for that calculation is above. It is the length multiplied by the width multiplied by the ceiling height.
- Next we will calculate how long our air scrubber takes to change the air one time. To do so, we will divide the room’s cubic feet from step 1 by the CFM of one air scrubber.
- Now that we know how long it takes for the air scrubber to change the air once, we will use that to determine how many times the air will be changed each hour of operation. To do so, we divide 60 minutes by the time it takes to change the air once (from step 2).
- Finally, we will divide the desired number of air changes per hour by the rate at which one of our scrubbers changes the air. This will tell us how many air scrubbers we need for the job.

Calculating the Number of Air Scrubbers for a Job

We got started by saying this was simple, but there’s a lot of math going on up there. Let’s put it all together with a clear example.

### Example #1: Remediation in a 18′ x 26′ x 14′ warehouse

For this example we will calculate the number of air scrubbers required for a remediation job. The size of the room we are focusing on is 18 feet long, 26 feet wide and has a 14 foot drop ceiling. For our example, we will be using a portable air scrubber rated at 500 CFM.

#### Calculating the number of air scrubbers required

Here are those steps using the inputs in our example:

- Room Size: 18′ x 26′ x 14′ = 6,552 cubic feet
- Single Air Change: 6,552 cubic feet / 500 CFM = 13.1 minutes to change the air
- Changes each hour: 60 minutes / 13.1 minutes = 4.58 changes per hour
- Number of air scrubbers: 6 / 4.58 = 1.31 machines (or at least 2 machines)

The calculation above tells us that we would require 2 air scrubbers for this job.

### Example #2: Remediation in 27,000 square foot building with 20′ ceilings

In this example, we are using a 27,000 square foot building with ceilings that are 20 feet high. We’ll calculate how many air scrubbers are needed for the job. Each of the air scrubbers in this example are capable of 2,000 CFM. The steps are just about identical to our first example. The only difference is that the length and width of our building are provided as square footage. We do still need to multiply that number by the height to get cubic feet, however.

#### Calculating the number of air scrubbers required

Here is the result:

- Room Size: 27,000 sq ft x 20′ = 540,000 cubic feet
- Single Air Change: 540,000 cubic feet / 2,000 CFM = 270 minutes to change the air
- Changes each hour: 60 minutes / 270 minutes = .22 changes per hour
- Number of air scrubbers: 6 / .22 = 27.3 machines (or at least 27 machines)

Clearly this is a much larger job! You can use these calculations for any job, big or small. Do take some time and get to know how many air changes per hour are recommended for different job types.