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- 1). Measure the square footage of each room in your building. This is done by measuring the length and width of each room and multiplying those two numbers together.
- 2). Add the square footage of each room together to get the square footage of the building.
- 3). Calculate the CFM (cubic feet per minute) requirement of the building. Your building will need 1 CFM per square foot. So if your building is 2,000 square feet, you'll need 2,000 CFM.
- 4). Calculate the size of the HVAC unit by taking the total CFM requirement and dividing it by 400. HVAC units are sized in "tons," and 400 CFM equals one ton. So if your building requires 2,000 CFM, the HVAC unit size you would need is a five ton unit.
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