Glossary · Heating, cooling & ventilation

Ton (of cooling)

Also called: ton of refrigeration · tonnage · cooling ton

A unit of heating and cooling capacity: one ton equals 12,000 BTU per hour (3.5 kW), based on the cooling from melting a ton of ice in a day.

What it means

The term is based on the cooling effect of melting a ton of ice over a day. Capacity changes with outdoor temperature, so a heat pump's rated tonnage isn't what it delivers in deep cold; check its capacity at your design temperature.

Why it matters in an audit

Rules of thumb like 'one ton per 500 square feet' tend to oversize equipment; a proper load calculation sets the right tonnage.

Typical numbers

Reference values with their sources. Your auditor’s report gives the figure for your own house.

What	Value	Source
Definition (NIST)	1 ton = 12,000 BTU/h = 3.517 kW	nist.gov ↗
Rule of thumb vs. calculation (ACCA blog, 2016)	Contractor rules of 400–600 ft² per ton vs. an average of 1,431 ft² per ton across 40 Manual J calculations	hvac-blog.acca.org ↗

Sources

Learn more here

Sizing heating and cooling: the load calculation →

Related terms

BTU and BTU/h A unit of heat energy; BTU per hour (BTU/h) measures how fast a furnace, heat pump or air conditioner delivers heating or cooling.
Load calculation An engineering calculation of how much heating and cooling a house needs, room by room, used to size equipment correctly.
Oversizing Installing heating or cooling equipment with much more capacity than the house needs, usually from rules of thumb, not a load calculation.
Short cycling When heating or cooling equipment turns on and off frequently in short bursts instead of running in steady, longer cycles.
Design temperature The cold (or hot) outdoor temperature a heating or cooling system is sized for; colder than most winter days, but not the record low.
Kilowatt (kW) A rate of using or producing energy equal to 1,000 watts; running 1 kW for an hour uses 1 kilowatt-hour (kWh), the unit on your electricity bill.
Manual S (ACCA equipment selection) The US industry standard for choosing heating and cooling equipment whose real capacity, from the maker's data, fits the home's calculated loads.

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