BTU Calculator
Estimate the cooling or heating needs of a room or house. Finding the correct BTU rating for your Air Conditioner or Heater ensures maximum comfort and energy efficiency.
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Comprehensive Guide to BTU & HVAC Sizing
What is a BTU?
BTU stands for British Thermal Unit. It is a traditional unit of heat defined as the amount of energy required to raise the temperature of one pound of water by one degree Fahrenheit. In the HVAC (Heating, Ventilation, and Air Conditioning) industry, BTU actually refers to BTU per hour (BTU/h)—the cooling or heating capacity a machine can deliver within an hour.
What is an "AC Ton"?
When you look at central air conditioning units, you will often see them rated in "Tons" rather than BTUs. This is a historical term originating from the days before mechanical refrigeration, when buildings were cooled using actual blocks of ice harvested in the winter.
1 AC Ton = 12,000 BTU/h
It takes exactly 288,000 BTUs to melt one ton (2,000 lbs) of ice in 24 hours. If you divide 288,000 by 24 hours, you get exactly 12,000 BTUs per hour! Therefore, a "2-Ton AC unit" has a capacity of 24,000 BTU/h.
General Rule of Thumb (Energy Star Guidelines)
While our calculator provides a highly tailored estimate based on your specific environmental factors, the US Department of Energy (Energy Star) provides this baseline chart for standard 8-foot ceiling rooms:
5,000 BTU
6,000 BTU
7,000 BTU
8,000 BTU
9,000 BTU
10,000 BTU
12,000 BTU
14,000 BTU
The Danger of Oversizing & Undersizing
An oversized AC cools the room down extremely quickly and then shuts off. Because the cooling cycle is so short ("short cycling"), the unit fails to extract humidity from the air. The room will reach the target temperature, but it will feel damp, "clammy", and uncomfortable. It also increases wear and tear on the compressor.
An undersized unit will run constantly without ever reaching the desired temperature on a hot day. This continuous operation consumes massive amounts of electricity and will eventually cause the machine's motor to overheat and burn out prematurely.