Price the system your house actually needs, before the quotes arrive
| System | Typical Installed Cost | Sizing Basis | Expected Life |
|---|---|---|---|
| Central AC only | $6,000 – $18,000 (3-ton) | 500–600 sq ft per ton | 12–17 yrs |
| Gas furnace only | $2,800 – $6,400 (80 kBTU) | 35–55 BTU/hr per sq ft climate-dependent | 15–25 yrs |
| Complete AC + furnace | $7,900 – $22,000 (3-ton + 80 kBTU) | Both rules above | 15–20 yrs system |
| Air-source heat pump (ducted) | $7,800 – $15,900 (3-ton) | Same tonnage rule; cold-climate units higher | 12–17 yrs |
| Ductless mini-split | $6,600 – $11,000 (3-zone) | 1 zone per 400–700 sq ft | 12–20 yrs |
Ranges assembled from published 2025–26 manufacturer and contractor pricing guides (Bryant's 2026 pricing guide puts full-system replacement at $5,000–$28,000 nationally; EnergySage's ducted heat-pump average is about $14,500). Equipment alone for a 3-ton AC runs $1,700–$5,000, so labor and materials drive most of the spread.
Most HVAC pricing tools ask for a zip code and hand you to a call center. This one does the arithmetic a good estimator does on the phone first: size the equipment from your square footage, apply realistic per-unit installed rates, and show the national band around your number so you can tell a fair quote from a padded one.
System size = home square footage ÷ square feet per ton, snapped to the standard half-ton increments (1.5, 2, 2.5, 3, 3.5, 4, 5). AC cost = tons × dollars per ton. Furnace cost = BTU rating in thousands × dollars per thousand BTU. A complete system gets a 10% bundle discount, since one crew, one permit, and one coil changeout cover both pieces. Mini-splits price as first zone plus added zones. SEER2 savings = annual cooling cost × (1 − old SEER2 ÷ new SEER2).
Enter your home's square footage and leave the sizing slider at 600 square feet per ton unless you know better: older, leakier homes run closer to 500, tight new construction 700 or more. Defaults sit at national midpoints, so swap in the per-ton or per-BTU price from a real quote to see where it lands. The SEER2 check tells you whether the efficiency upgrade pays in your climate.
An 1,800 sq ft house at 600 square feet per ton needs a 3-ton system. AC only at the $3,500-per-ton default: $10,500, inside a national range of $6,000 to $18,000. A matching 80,000 BTU gas furnace at $55 per thousand BTU adds $4,400. Together, with the 10% bundle discount, $13,410, in a band running $7,920 to $21,960.
The efficiency math is smaller than the sales pitch suggests. Going from the 14.3 SEER2 minimum to 17 SEER2 saves 1 − 14.3 ÷ 17 = 15.9% of cooling energy. On $600 a year of cooling that's $95 a year, so a $2,000 efficiency premium takes 21 years to pay back in a mild climate and closer to 8 in Phoenix. Run your own numbers before paying for the top-tier badge.
A complete 3-ton AC plus gas furnace replacement typically runs $7,900 to $22,000 installed, with most jobs landing between $8,000 and $15,000. AC alone runs $6,000 to $18,000 for a 3-ton system, and a gas furnace alone runs $2,800 to $6,400. High-efficiency equipment pushes toward the top of each range.
Roughly 3 to 4 tons. The common industry rule is 500 to 600 square feet per ton of cooling, so 2,000 sq ft suggests 3.3 to 4 tons. Insulation, ceiling height, sun exposure, and climate shift it a full half-ton either way, and a Manual J load calculation is the only way to size it right. Oversizing short-cycles the unit and wrecks dehumidification.
Often similar or slightly higher upfront: a 3-ton ducted air-source heat pump runs about $7,800 to $15,900 installed versus $7,900 to $22,000 for the AC-plus-furnace combo, but you skip having two systems. In cold climates a cold-climate heat pump or dual-fuel setup costs more. Operating cost depends on your gas versus electric price ratio.
Moving from the 14.3 SEER2 minimum to 17 SEER2 cuts cooling energy use by about 16%, since savings equal 1 minus old rating divided by new rating. On $600 a year of cooling, that's about $95 a year. Payback on the upgrade typically runs 8 to 15 years, so it makes most sense in hot climates with long cooling seasons.
Central AC units and air-source heat pumps last 12 to 17 years on average; gas furnaces 15 to 25 years because they have fewer mechanical parts and sit idle all summer. Coastal salt air, poor installation charge levels, and skipped filter changes all shorten life. If a repair quote passes half the replacement cost on a unit past 12 years, replacing usually wins.
Equipment is only 30 to 50% of the invoice. Labor, ductwork modifications, line-set replacement, permits, and company overhead do the rest, and those swing by region and contractor. That's why the same 3-ton changeout draws quotes from $6,000 to $18,000. Three written quotes is the minimum before signing.