Sizing
Ton
An HVAC capacity unit equal to 12,000 BTU per hour of heat-transfer rate.
What is Ton?
A ton of refrigeration is a heat-transfer rate equal to 12,000 BTU per hour. HVAC systems are frequently grouped into nominal tonnage sizes, so a 24,000 BTU/hr system is commonly called two tons and a 36,000 BTU/hr system is commonly called three tons.
Tonnage describes cooling capacity, not equipment weight. NIST lists one ton of refrigeration as 12,000 Btu_IT per hour, equivalent to approximately 3,516.853 watts of thermal transfer.
Nominal tonnage is a convenient size class. Variable-capacity equipment may operate across a broad range, and certified capacity at a particular rating condition may not equal the round nominal number in the product name.
Why it matters
Tonnage is widely used in bids, model families, and equipment selection. Correct sizing still requires a building load calculation rather than choosing equipment from square footage alone.
Formula / Conversion
1 ton of refrigeration = 12,000 Btu/hr ≈ 3.5169 kW of thermal transfer
Sources
HVACBird prioritizes government standards bodies, federal test procedures, and recognized HVAC certification organizations for technical definitions.
National Institute of Standards and Technology (NIST)
NIST conversion entry for a ton of refrigeration and its 12,000 Btu/hr definition.