How the size estimate works
Cooling equipment is sold in tons: one ton removes 12,000 BTU of heat per hour. The calculator divides your conditioned floor area by a rule-of-thumb coverage figure — 400 sq ft per ton in hot climates, 500 in mixed climates and 600 where summers are mild — and rounds to the nearest half ton. Residential split systems run from about 1.5 to 5 tons, so results are kept inside that range.
Treat that number as a sanity check, not a design. Two 2,000 sq ft houses can need very different equipment depending on insulation, window area and orientation, duct leakage and ceiling height. Contractors size systems with an ACCA Manual J load calculation, and you should ask for one in writing. If a bid simply matches the tonnage of your old unit, ask why — older systems were often oversized.
Worked example: 2,000 sq ft, mixed climate
| Step | Calculation | Result |
|---|---|---|
| Size | 2,000 sq ft ÷ 500 sq ft per ton | 4 tons |
| Installed cost | 4-ton central AC, national average | $6,500 – $8,800 (midpoint $7,650) |
| Current cooling energy | 4 × 12,000 × 1,200 h ÷ (SEER2 10 × 1,000) | 5,760 kWh/yr |
| New cooling energy | 4 × 12,000 × 1,200 h ÷ (SEER2 15 × 1,000) | 3,840 kWh/yr |
| Savings | 1,920 kWh × $0.182 | $349 per year |
| Simple payback | $7,650 ÷ $349 | about 21.9 years |
A 22-year payback looks poor, but that is the wrong way to read it for most replacements. If your old system has failed or is near the end of its life, you are paying for a new unit either way — the real question is how much extra a higher-efficiency model costs and how fast the difference pays back.
How much does efficiency matter?
SEER2 is the seasonal cooling efficiency rating used since 2023. Electricity use falls in direct proportion as the rating rises, so with the same 4-ton system and 1,200 cooling hours at $0.182/kWh:
| SEER2 | Energy | Cooling cost per year |
|---|---|---|
| 13 | 4,431 kWh | $806 |
| 15 | 3,840 kWh | $699 |
| 17 | 3,388 kWh | $617 |
| 20 | 2,880 kWh | $524 |
Going from 15 to 20 saves about $175 a year in this example. That is worth it in Phoenix or Houston, where cooling hours can be double the default, or wherever electricity costs 30¢ or more. In a cool northern climate with a few hundred cooling hours, a mid-range unit is usually the better buy. Set the cooling hours and rate to match your area before deciding.
Which system type?
- Central AC prices come from 2-, 3-, 4- and 5-ton installed price ranges. Half sizes are priced at the next size up.
- Heat pumps use the whole-home system range of $10,000–$25,000, which covers higher-end and cold-climate installs. A simple ducted swap can fall in the narrower $4,237–$7,943 survey range, so get quotes before ruling one out. Heating savings versus gas or electric resistance heat are not counted here, and they are often the main reason to choose a heat pump.
- Gas furnace replacement runs $2,823–$6,897 nationally. No cooling savings apply.
- AC + furnace adds the two ranges. Replacing both at once lets the installer match the indoor coil and blower to the new outdoor unit.
Every range is multiplied by the local cost level you pick. Large coastal metros often run 20–40% above the national figures.
What raises the price
Expect higher quotes for new or resized ductwork, a new electrical circuit or panel upgrade, a condensate pump, a hard-to-reach attic or crawlspace, refrigerant line replacement, permits and inspections, and variable-speed or two-stage equipment. Ask each contractor to list these separately so bids are comparable.
Related calculators
Cutting the heat load first can let you buy a smaller system — see the insulation calculator and window replacement cost calculator. To check what your current AC costs to run, try the electricity cost calculator, and if you are also weighing panels, the solar payback calculator.
How this calculator works
- Tonnage = floor area ÷ sq ft per ton, rounded to the nearest 0.5 ton and limited to 1.5–5 tons.
- Installed cost = dataset price range for the system × local cost level. AC + furnace adds the two ranges.
- Annual cooling kWh = tons × 12,000 BTU/h × cooling hours ÷ (SEER2 × 1000). Savings = (current kWh − new kWh) × rate.
- Simple payback = midpoint installed cost ÷ annual savings; it is shown as n/a when savings are zero or negative.
Assumptions and limitations
- Size uses a rule of thumb from the dataset's 400–600 sq ft per ton range: 400 for hot, 500 for mixed and 600 for cold climates. Assigning the range ends to climates is an editorial simplification.
- Central AC prices come from 2-, 3-, 4- and 5-ton installed price rows; half sizes are priced at the next size up.
- Heat pumps use the whole-home system range ($10,000–$25,000). A narrower survey range of $4,237–$7,943 reflects simpler ducted swaps.
- Prices assume replacement on existing, sound ductwork. New ducts, electrical upgrades and permits are extra.
- Energy savings cover cooling only, at constant full-load hours and a flat electricity rate. Heat pump heating savings are not modeled.
These results are planning estimates, not quotes. Local prices, site conditions and building codes vary, so get written estimates from licensed contractors before you commit to a budget.
Try your own numbers. Every price and assumption above is editable in the estimator.
Back to the hvac replacement estimatorFrequently asked questions
How do I know what size AC I need?
Is a higher SEER2 rating worth it?
Should I replace the furnace and AC at the same time?
Sources and data
- HomeGuide (2026) — install ac unit cost
- This Old House (2026) — 4 ton ac unit cost
- HomeAdvisor — install a heat pump
- HomeGuide (2026) — heat pump cost
- HomeAdvisor (2026) — install a furnace
- Trane — how many tons should my central ac unit be
- EIA Short-Term Energy Outlook (Sept 2026) — elec coal renew.php
- EnergySage — house watts
Prices are US national ranges reviewed October 2026 (data version 2026.10). A few values are editorial estimates where no single published source exists; the Cost Index marks each one. Read our methodology and editorial policy.