About

Selecting an air conditioner is not just about measuring square footage. An undersized unit will run continuously without cooling the space, driving up electricity bills. An oversized unit will cool the air too quickly without removing humidity, leading to a damp, clammy environment (short-cycling).

This calculator adheres to HVAC industry standards by calculating the Total Cooling Load. It aggregates heat gain factors including solar radiation through windows, metabolic heat from occupants, and volume-based requirements for high ceilings. Use this to determine the exact British Thermal Units (BTU) or Kilowatts (kW) needed for comfort.

Formulas

The Total Heat Load H_total is a summation of environmental variables:

H_total = (Area × 20) + (People × 600) + Q_sun + Q_kitchen

If ceiling height h is greater than standard (8 ft), a volume adjustment is applied:

Adjustment = (h - 8) × 1000

Reference Data

Factor	Heat Load Adder	Reasoning
Base Area Load	20 BTU/sq.ft	Standard residential insulation
High Ceiling (>8ft)	+1,000 BTU per ft	Increased air volume
Occupants	+600 BTU/person	Metabolic heat release
Kitchen Area	+4,000 BTU	Appliances/Oven heat
Sunny Windows	+10% Total	Solar gain (Radiant heat)
Heavy Shade	-10% Total	Reduced exterior temp

Frequently Asked Questions

BTU stands for British Thermal Unit. It is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. In AC terms, it measures how much heat the unit can remove from the air per hour.

No. An oversized AC cools the room so fast that it shuts off before it has a chance to dehumidify the air. This leaves the room feeling sticky and causes wear on the compressor due to frequent on/off cycles.

1 Ton of cooling is equal to 12,000 BTU/hr. Large central air systems are usually rated in Tons (e.g., a 3-Ton unit = 36,000 BTU).

Yes. The standard 20 BTU/sq.ft rule assumes average insulation. If you have poor insulation (drafty windows, thin walls), you should increase your calculated requirement by 15-20%.