Heat load Calculation- Thumb Rule

Common HVAC thumb rule:


400 cfm per ton of cooling is required for a comfort application.

500 cfm per ton of cooling for heat pump and high sensible heat load application.

350 cfm per ton of cooling for latent heat applications.

One cfm is needed per square feet of floor area.

For Example:

To calculate the number of tons required to cool a 2000 sqft office.

As per rule 1 cfm is required per 1 sqft of floor area.

Hence 2000 sqft needs 2000 cfm.

400 cfm required per ton.

2000 cfm required 5 ton to cool the office.

6 to 10 air changes per hour.

This is the average number of times in each hour that the air in the room is removed and replaced by circulating the air.

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