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Units of Measureaka: ton of refrigerationaka: TRaka: cooling ton

Ton (mechanical)

In Plain English

A unit of cooling capacity for HVAC systems, equal to 12,000 BTUs per hour.

Definition

In HVAC and mechanical engineering, a ton is a unit of cooling capacity equal to 12,000 British Thermal Units (BTUs) per hour. The term derives from the amount of heat required to melt one ton of ice in 24 hours. Air conditioning equipment—chillers, cooling towers, rooftop units, and split systems—is sized and specified in tons of cooling, and building cooling loads are calculated in tons to select appropriately sized equipment.

Why It Matters in Bidding

Cooling tonnage drives the single largest line item in most mechanical bids, so a misread on the engineer's load calculation can swing equipment, electrical service, and structural support costs significantly. Estimators price chillers, RTUs, and split systems per ton, and the tonnage also dictates duct sizing, refrigerant piping, and crane or rigging needs.

Example

Reviewing the mechanical schedule, an estimator confirms the rooftop unit is specified at 25 tons and prices it, the curb adapter, and a crane lift accordingly before sending the package out to HVAC subs.

Related Terms

MEP (Mechanical, Electrical, Plumbing)ASHRAEUnit Price

Frequently Asked Questions

Rule-of-thumb rough estimates often land around 400 to 600 square feet per ton, but bidding should never rely on this. Always price from the engineer's actual load calculation, since occupancy, glazing, climate, and internal heat gains drastically change tonnage and using rules of thumb invites scope gaps.
Equipment manufacturers and the trade catalog cooling capacity in tons because it produces cleaner, comparable nominal sizes. Since one ton equals 12,000 BTU/hr, estimators can quickly match a load to a standard unit size, compare sub quotes apples-to-apples, and verify the design against the equipment schedule.
Generally yes for equipment, but oversizing also inflates electrical service, breaker sizing, structural curbs, and operating cost, which can hurt a design-build bid on lifecycle value. On hard-bid jobs you price exactly what the documents specify and submit any oversizing concerns through RFIs rather than self-adjusting tonnage.

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