In short
AC tonnage is cooling capacity, not weight. One ton equals 12,000 BTU per hour, so a 2.5-ton air conditioner removes 30,000 BTU of heat from the house every hour. Most houses in the GTA and Hamilton area need between 1.5 and 3.5 tons, and the right figure comes from a heat-gain calculation, not from square footage alone.
AC tonnage is the first number on an air conditioner quote, and it describes how much heat the unit carries out of your house each hour. The word comes from the days when buildings were cooled with blocks of ice. It sits with the other rating terms in the ZK Mechanical glossary.
What one ton of cooling means
One ton of cooling is 12,000 BTU per hour. A 2,000-pound block of ice absorbs 288,000 BTU as it melts, and spread over 24 hours that works out to 12,000 BTU every hour. Residential air conditioners are built in half-ton steps.
- 1.5 tons = 18,000 BTU per hour
- 2 tons = 24,000 BTU per hour
- 2.5 tons = 30,000 BTU per hour
- 3 tons = 36,000 BTU per hour
- 3.5 tons = 42,000 BTU per hour
- 4 tons = 48,000 BTU per hour
- 5 tons = 60,000 BTU per hour
How to read tonnage from the model number on the nameplate
The tonnage is coded into the model number on the outdoor unit's nameplate as the capacity in thousands of BTU. Look for a two- or three-digit number that divides evenly by 6: 018 is 1.5 tons, 024 is 2, 030 is 2.5, 036 is 3, 042 is 3.5, 048 is 4 and 060 is 5. Divide the number by 12 to get tons. A few manufacturers code it differently, and in that case the spec sheet for the model number settles it.
Why the right tonnage matters in a humid Ontario summer
A bigger air conditioner is not a better one. An oversized unit drops the air temperature fast and shuts off before it has run long enough to pull moisture out, so the house reads 23°C and still feels clammy. That shows up along the Lake Ontario shoreline in Burlington, Oakville and Mississauga, where lake humidity is the larger part of the discomfort. An undersized unit has the opposite problem: it runs without a break through a heat wave and the upstairs keeps climbing.
- Signs of too many tons: cycles of ten minutes or less, sticky air at a normal thermostat reading, loud rushes of air from the vents
- Signs of too few tons: the unit never shuts off on hot afternoons and the indoor temperature rises anyway
- Signs the size is right: long, steady cycles on hot days and a house that feels dry at the set temperature
Proper sizing comes from a CSA F280 calculation of the home's heat gain, which counts window area and direction, insulation, air leakage and occupants. Two houses with the same floor area can land half a ton apart: a 1960s bungalow with original windows gains heat very differently from a 2000s build. The square-footage ranges and worked examples are in our guide to what size air conditioner you need.
What tonnage means for the price of a new air conditioner
Central air runs $3,500–$7,500 installed where ducts already exist, and larger tonnage and higher efficiency both push toward the upper end. Tonnage also has to match what is indoors. The furnace blower and ducts need to move roughly 400 cubic feet of air per minute for each ton, so going up a size can mean duct changes, not only a bigger outdoor unit.
If a quote simply matches the tonnage of the old unit, ask how that number was checked. ZK Mechanical sizes every air conditioner installation from the house, not the old nameplate, and puts the tonnage and model number in writing. To have yours looked at, book a free quote.
Questions people ask about AC tonnage
How many tons of AC do I need for a 2,000 square foot house?
Square footage alone will not settle it. A 2,000-square-foot house in this area commonly lands between 2 and 3 tons, and which end depends on window area, insulation, sun exposure and air leakage. A newer, tighter house can need less cooling than an older, smaller one. A heat-gain calculation done room by room gives the number to buy.
Does a 3-ton air conditioner weigh three tons?
No. Tonnage is a rate of heat removal, 12,000 BTU per hour for each ton, and has no connection to the weight of the equipment. A 3-ton outdoor unit is somewhat larger and heavier than a 2-ton one because it has a bigger coil and compressor, but two people can still carry it.
Can I replace my 2-ton air conditioner with a 3-ton to cool the house faster?
It usually makes the house less comfortable. The indoor coil, blower and ducts were sized for 2 tons, so a 3-ton unit short-cycles, removes less humidity and wears its compressor with frequent starts. If the house will not cool, look first at a dirty coil, low refrigerant, leaky ducts or attic insulation. Those fix the cause.