Why divide by 12,000?

One ton of refrigeration equals 12,000 BTU/h, defined as the heat needed to melt one ton (2,000 lb) of ice in 24 hours. Dividing a cooling load in BTU/h by 12,000 converts it directly to tons of refrigeration.

What is the Manual S sizing window?

ACCA Manual S recommends selecting cooling equipment with total capacity between 90 and 115 percent of the calculated cooling load for most systems, and not exceeding 115 percent to avoid short cycling. This tool uses a 95 to 115 percent window as a practical default and flags sizes outside it.

Why not just round up to the next ton?

Oversized equipment short-cycles, removes less humidity, wears out faster, and costs more to run. Manual S deliberately limits oversizing. Rounding up by a full ton on a small load can push you well past 115 percent of the load, which is poor practice.

Does this include heating?

No. Tonnage refers to cooling capacity only. Heating is sized separately in BTU/h or kW and uses Manual S guidance specific to furnaces, heat pumps, or hydronic equipment. Use this tool for the cooling side.

What about latent versus sensible load?

Enter the total cooling load (sensible plus latent) in BTU/h. Manual S equipment selection then checks that the chosen unit's published sensible and latent split at your design conditions actually covers both components, which you verify against the manufacturer's expanded performance data.

HVAC Tonnage Calculator

The HVAC tonnage calculator converts a cooling load in BTU/h into tons of refrigeration and recommends a standard equipment size using ACCA Manual S logic. It is the bridge between a Manual J load calculation and picking an actual condensing unit off the shelf.

How it works

Conversion and sizing follow two simple rules:

tons        = cooling load (BTU/h) / 12,000
min size    = 0.95 x load   (95% of load)
max size    = 1.15 x load   (115% of load, Manual S cap)

One ton equals 12,000 BTU/h. Manual S then constrains equipment selection to a window around the calculated load so the unit is large enough to meet design conditions but not so large that it short-cycles and fails to dehumidify. The tool rounds to the nearest standard 0.5-ton increment and confirms that size lands inside the window.

How it works (continued)

Standard residential and light-commercial equipment comes in 0.5-ton steps (1.5, 2.0, 2.5, 3.0 tons and so on). The tool snaps the exact tonnage to the closest standard size and then verifies it against the 95 to 115 percent window, flagging if the nearest standard size is undersized or oversized.

Example and tips

A 30,000 BTU/h cooling load is 30000 / 12000 = 2.5 tons exactly, so a 2.5-ton unit is a clean match. A 26,500 BTU/h load is 2.21 tons; the Manual S window runs from 25,175 to 30,475 BTU/h, so a 2.5-ton (30,000 BTU/h) unit fits, while a 2.0-ton (24,000 BTU/h) unit would be undersized. Always size from a real Manual J load, never from square footage rules of thumb, which routinely oversize equipment by a full ton or more.