How to Size an Air Cooler by CFM and Floor Area
Tank capacity tells you how often somebody refills the machine. Airflow tells you whether the space will actually feel cooler. Sizing an evaporative cooler starts from the air volume you need to move, not from the litres printed on the front.
Quick answer: Work out the room volume in cubic feet, decide how many times per hour you want that air replaced, and divide by 60. That gives the airflow in CFM the cooler must deliver. Everything else, including tank size, follows from that number.
The formula
Evaporative coolers are sized on air changes, because they work by replacing air rather than recirculating it. The calculation is:
CFM = (length × width × height in feet) × air changes per hour ÷ 60
Cubic feet per minute is simply the room volume divided by how many minutes you want one complete air change to take.
| Space | Air changes per hour | Notes |
|---|---|---|
| Living room or office | 15 to 20 | Comfort cooling, low heat load |
| Shop or showroom | 20 to 30 | Door opening frequently, people moving |
| Workshop | 30 to 40 | Machinery adds heat |
| Factory floor or warehouse | 40 to 60 | High roof, high heat load, wide area |
| Kitchen or high-heat area | 50 to 60 | Concentrated heat sources |
A worked example
Take a workshop 60 ft long, 40 ft wide, with a 14 ft clear height. The volume is 60 × 40 × 14, which is 33,600 cubic feet.
At 40 air changes per hour: 33,600 × 40 ÷ 60 = 22,400 CFM.
That is the total airflow requirement. It rarely means one machine. Splitting it across several units placed along the working lanes gives more even coverage than a single large unit at one end, and keeps working if one is down for maintenance.
Height matters more than people expect
Floor area alone is a poor guide, because a shed with a 20 ft roof holds far more air than an office of the same footprint. Always use clear height in the volume calculation.
In very high buildings, cooling the entire volume is wasteful. The usual approach is to treat the occupied zone near floor level as the target and direct airflow there, rather than conditioning air near the roof that nobody is standing in.
Throw distance and placement
Airflow only helps where it arrives. Each unit has a practical throw, and beyond it the air has mixed with the surrounding air and the cooling sensation drops off.
Place units so their airflow crosses where people actually work, draw fresh air from outside rather than from an already-warm interior, and leave an exhaust path on the opposite side. Cooled air pushed into a sealed corner simply raises humidity there.
Then check the other numbers
Once the CFM requirement is set, compare candidate models on total power at that airflow, water consumption per hour, pad type and depth, and the space needed to service the tank and pads. Tank capacity now becomes a refill-interval question rather than a sizing one.
For running cost against air conditioning, see air cooler vs air conditioner running cost. For pad selection, see cellulose pad vs honeycomb pad.
Common questions
What CFM air cooler do I need for a 1000 sq ft area?
Multiply by the clear height to get volume, then apply an air change rate. At 12 ft height that is 12,000 cubic feet; at 30 air changes per hour the requirement is about 6,000 CFM. Raise the air change rate for hotter or busier spaces.
Is a higher CFM always better?
Higher airflow covers more area, but airflow you cannot exhaust becomes humidity rather than cooling. Size to the space and make sure there is a fresh air inlet and an outlet.
Should I use one large cooler or several smaller ones?
For wide floors, several units distributed along the working lanes usually give more even coverage than a single unit, and production is not stopped when one is serviced.
Does tank capacity tell me the cooling capacity?
No. Tank capacity sets how long the unit runs between refills. Cooling is determined by airflow, pad area and how dry the incoming air is.
Related cooling information
Capacity calculator
Plan production output for cooling pad manufacturing.
Air cooler range
Compare confirmed capacities and dimensions.
Factory and warehouse cooling
Placement across a working floor.