Sizing & efficiency
AC tonnage chart: what size unit do I need?
As a starting point, North Texas homes need roughly one ton of cooling per 450 to 550 square feet — so a 2,000 sq ft house lands somewhere around 3.5 to 4.5 tons. The chart below g...
As a starting point, North Texas homes need roughly one ton of cooling per 450 to 550 square feet — so a 2,000 sq ft house lands somewhere around 3.5 to 4.5 tons. The chart below gets you into the right bracket. It should not be what sizes your system, and the reason is worth two minutes: the same 2,000 sq ft house can genuinely need 3 tons or 5, depending on which way it faces and how much glass it has.
| Home size | Typical range (North Texas) |
|---|---|
| 1,000 – 1,300 sq ft | 2 – 2.5 tons |
| 1,300 – 1,600 sq ft | 2.5 – 3 tons |
| 1,600 – 2,000 sq ft | 3 – 3.5 tons |
| 2,000 – 2,500 sq ft | 3.5 – 4.5 tons |
| 2,500 – 3,000 sq ft | 4 – 5 tons |
| 3,000 – 3,500 sq ft | 5 – 6 tons, often two systems |
| 3,500+ sq ft | Usually two systems |
One ton = 12,000 BTU/hr. Texas ranges run tighter per square foot than national charts, because the cooling load here is higher.
The five things that move the answer
- Orientation and glazing. West-facing glass is the single biggest variable in North Texas. A house with a wall of west-facing windows can need a full ton more than an identical house turned 90 degrees.
- Insulation and age. A 2015 build with modern insulation and low-E windows needs measurably less than a 1985 house of the same size.
- Ceiling height. Charts assume 8-foot ceilings. Two-storey entries and vaulted living rooms add volume that square footage does not capture.
- Shade. Mature trees are worth real capacity — one reason established Richardson and Plano neighbourhoods often size lower than their square footage suggests.
- Duct capacity. The hard ceiling. A five-ton system on ducts that can carry three tons of airflow delivers three tons of cooling, and wears out early doing it.
Why bigger is not safer
Rounding up “to be safe” is the most common sizing error in the trade, and it produces a worse result rather than a conservative one.
An oversized system cools the air quickly, satisfies the thermostat, and shuts off before it has removed much humidity. Dehumidification takes run time. So the house ends up cold and clammy at once — the specific complaint we hear most often in Frisco’s newer housing stock. Oversizing also short-cycles the compressor and masks duct problems it cannot fix.
Two storeys change the question entirely
Heat rises and upstairs runs warmer. A single system serving both floors is a compromise however it is sized. The real answers are zoning, a second system, or fixing the duct balance — not more tonnage.
What a Manual J actually does
It is the industry-standard load calculation: room by room, working from orientation, window area and type, insulation values, ceiling heights, infiltration, occupancy and local design temperatures. It takes about forty minutes on site and produces a number that reflects your house rather than its floor area.
Why per-square-foot rules vary so much between sources
You will find charts quoting anywhere from 400 to 700 square feet per ton, which is a wide enough spread to be useless without context. The reason is that the rule bundles climate and construction quality into one number.
A 600 sq ft per ton figure assumes a mild climate or a well-sealed modern envelope. A 400 sq ft per ton figure assumes a hot climate or a leaky older house. North Texas sits at the demanding end of the climate scale, which is why the 450–550 band above is tighter and lower than the national charts — and why using a national chart here tends to undersize on paper before the contractor overcorrects by rounding up.
A worked example
Two 2,300 sq ft houses in Frisco, both two-storey, both built in 2006.
House A faces north, has mature trees along the west side, standard window area, and a decently sealed attic. It lands around 3.5 tons.
House B faces west, has a two-storey entry with a tall glazed panel, a wall of west-facing windows in the living room, and no shade. Same floor area, and it lands at 4.5 tons — a full ton more, entirely because of orientation and glass.
A chart cannot tell those two houses apart. That is the whole argument for the load calculation, and it is why we will not quote tonnage over the phone.
Half-tons and why systems come in the sizes they do
Residential equipment is sold in half-ton increments — 2, 2.5, 3, 3.5, 4, 5 tons. There is no 3.7-ton unit. So the load calculation produces a number and then you round to the nearest available size, which is where judgement enters.
The convention worth knowing: on the cooling side, when a calculation lands between two sizes, rounding down is usually the better error in a humid climate, because the smaller unit runs longer and dehumidifies better. Rounding up is the error most of the trade makes by default.
How to sanity-check a quote you already have
Ask what tonnage they are proposing and how they arrived at it. “Same as what is there now” means nobody calculated anything. Ask whether they measured static pressure. Ask whether they looked at the returns. A contractor who has done a load calculation will be pleased to be asked; one who has not will change the subject.
Want this priced for your house?
The figures above are general market ranges. For what it actually costs at your address, we do a free load calculation and give you one fixed written quote — itemised, valid for 30 days, and with no sales presentation attached.
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