The Importance of CFM/CMH When Choosing an Evaporative Cooler

Last updated Feb. 26, 2021

Air coolers are wonderful – that is only when you buy the right one for your home or commercial space. If you are conversant with these air cooling solutions and how they work, you will know that taking your time to pick the right one matters a lot.

One of the most important factors to consider when choosing an evaporative cooler is the CFM/CMH. What does that mean, and why does it matter?

To answer these and other important questions, we have to start with how evaporative air coolers work.

How Do Evaporative Air Coolers Work? 

Evaporative are coolers are simple machines that rely on the evaporative cooling process to keep a space cool and comfortable for humans. The evaporative cooling process is a natural process that involves the use of air and water.

It works with the same principle that makes the body cool after getting out of a swimming pool or any body of water at all.

Evaporative air coolers work by taking in warm, dry air from the surrounding, passing the warm air through a moistened pad, and releasing cool air to the surrounding area.

The moistened pads are able to suck in dry air, and they are aided by the fan system that helps to draw the warm air into the machine.

The actual cooling in the evaporative air cooler happens on the moistened pads – this is why they are called cooling pads.

As the hot, dry air pass through the pads, the pads absorb the heat from the air, using it to bring about the evaporation of the moisture on the pads.

The temperature of the air can be reduced by as much as 20 degrees.

After the temperature of the air has been reduced, the resultant cool air is expelled from the air cooler by the blower system.

Some level of moisture is also added to the cool air as they are expelled from the machine towards the space that needs to be cooled.

The process will be repeated continuously as long as the machine is on, and the conditions are ideal for evaporative cooling.

For the condition to be ideal for evaporative cooling, the air cooler must receive an adequate supply of warm, dry air.

There must also be a way for stale air in the room to be moved out to avoid moisture buildup. This is where the size of the machine you are using matters.


What is CFM/CMH?

CFM stands for cubic feet per minute, while CFH stands for cubic feet per hour. The two terms refer to the amount of air an evaporative air cooler will be able to pump in a minute or in one hour.

Every air cooler has a CFM or CFH rating, and you just have to figure out the CFM or CFH requirement of the space you want to cool.

It can also be helpful to figure out the speed of air. Ideally, it is expressed in feet per second (FPS) or meters per second (MPS).

Sufficient airspeed is important to keep the performance of the air cooler optimized. This is because the absorption rate is increased by higher velocity.

This implies that the higher the airspeed, the better the cooling pads can absorb heat energy from the air.

While the CFM/CMH rating of the air cooler is the most important thing to look out for in terms of size, you should know that airspeed matters too. The optimal speed of air is given as 3.4 MPS.


Choosing the Right Size of Evaporative Air Cooler

If you are planning to buy an air cooler and want to get it right with size, you will have to figure out your CFM requirement before looking for a machine that will meet it.

This requires a simple calculation you will need to perform on your own. If you feel you are not equal to it, you can invite a professional to take the measurements, perform the calculation, and recommend the right machine.

To determine the exact CFM you need for a specific room, follow the steps below.

Step 1: Measure the room’s width and length. Multiply the two value to arrive at the square footage of the room

Step 2: Measure the height of the room from the ceiling to the floor.

Step 3: Multiply the square footage by the ceiling height to determine the cubic feet. You can also measure the width, the length, and the ceiling height at the same time and multiply the three values in feet to determine the cubic footage.

Step 4: Divide the number you get by two to arrive at two air changes per minute, which will define the CFM requirement.

For Example: If the length of the room is 15 feet, the width 10 feet, and the ceiling height is 8 feet, here is how the calculation will look like:

  • Square footage = 15 x 10 = 150
  • Cubic footage = 150 x 8 = 1,200
  • CFM = 1,200/2 = 600 CFM for the room.

You can apply this formula to calculate the CFM requirement of the entire house. You just have to estimate the square footage of the house, get the average ceiling height and follow the same procedure to determine the CFM requirement.


Other Considerations

While getting the CFM requirement of your room or house is very important in choosing the right size of air cooler, it is not the only important thing to consider.

Actually, CFM only determines cooling capacity. You need to consider other factors like special features, water-tank capacity, drainage options, and even the design of the air cooler you intend to buy.


The evaporative air cooler can be the perfect machine for you if you live in a hot, dry climate, where it is most efficient. However, you will have to buy the right size to get all the benefits it offers.

Figuring out the perfect size for your room or house shouldn't be a big deal. We have illustrated just how you can do that.

If you are overwhelmed by the processes involved in estimating the CFM requirement of a home or a commercial building, involving a technician can be helpful.

A professional can help you figure out the right size of the machine, as well as the very best option for any space at all.

If you have any further questions, contact us and we would be pleased to help you.


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