Cooling Load Calculator

Work out cooling load instantly with clear inputs, formula shown and shareable results.

About Cooling Load Calculator

A room cooling load is the sum of the heat pushed in through the envelope and the heat generated inside it. This estimate applies a 25 BTU/h per square foot envelope baseline, scales it for ceiling height and solar exposure, then adds roughly 500 BTU/h of sensible plus latent gain per occupant. Dividing by 12,000 converts the load into nominal tons of refrigeration.

Formulas

Cooling load

Load = area x 25 x exposure factor x (height / 8) + occupants x 500; tons = load / 12000

area: Conditioned floor area (ft²)
exposure factor: 0.90 shaded, 1.00 average, 1.15 sunny

Supply airflow

CFM = sensible BTU/h / (1.08 x supply air ΔT)

Worked example

With the default values below, Cooling Load Calculator returns Total cooling load of 18,375. Change any input above and every figure here is recalculated in your browser.

Inputs used

Floor areaminimum 1 ft²: 600 ft²
Ceiling heightminimum 6 ft: 9 ft
Occupantsminimum 1: 3
Sun exposureone of Heavily shaded, Average, Sunny / west facing: Average

Results

Total cooling load: 18,375 BTU/h
Capacity required: 1.53 tons
Supply airflow at 20 °F ΔT: 851 CFM
Load intensity: 30.6 BTU/h/ft²

Step by step

1Values used
2Cooling load
3Supply airflow
4Total cooling load= 18,375 BTU/h
5Capacity required= 1.53 tons
6Supply airflow at 20 °F ΔT= 851 CFM
7Load intensity= 30.6 BTU/h/ft²

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Preliminary estimate only. A Manual J or equivalent room-by-room load calculation by a qualified HVAC engineer is required for equipment selection and code compliance.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Preliminary estimate only. A Manual J or equivalent room-by-room load calculation by a qualified HVAC engineer is required for equipment selection and code compliance.

Frequently Asked Questions

How is the Cooling Load figure worked out?

Load = area x 25 x exposure factor x (height / 8) + occupants x 500; tons = load / 12000. A room cooling load is the sum of the heat pushed in through the envelope and the heat generated inside it.

Why does ceiling height change the answer?

Load rules of thumb are calibrated to 8 ft ceilings. A taller room holds more air to cool and more wall area to gain heat through, so the load scales roughly with the height ratio.

What values do I need to enter?

This calculator takes 4 inputs: Floor area, Ceiling height, Occupants, Sun exposure. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.