HVAC replacement cost calculator — full furnace + AC change-out

How this estimate is built

The calculator does five things, all in the open:

1. Size from square footage. Your home size maps to a cooling capacity range using the 1-ton-per-400–600 sq ft rule (1,800 sq ft lands at 3–3.5 tons and an 80,000 BTU furnace class). Costs are priced at the lower bound of that range. This is a budget-planning shortcut, not sizing advice — our HVAC sizing estimator shows the full capacity math by climate and insulation, and a contractor's ACCA Manual J load calculation is the real answer.
2. Furnace list price. Each package carries a published distributor list price for the gas furnace — for example, $1,733 for a Goodman 80% AFUE 80,000 BTU unit and $1,883 for the 96% AFUE equivalent, both pulled from HVACDirect.com product pages in July 2026. A July-4th sale showed those same units about 20% below list, and that observed sale floor is what anchors our low band. The 97% modulating band is inferred from the Goodman price ladder and flagged as interpolated in the dataset.
3. AC list price. The condenser price comes from the same dataset our AC replacement calculator uses: $2,276–$4,322 at 3 tons depending on SEER2 tier, plus a matched evaporator coil at $900–1,500. The two calculators share one price table by design, so they can never quietly disagree.
4. Contractor markup and labor. Equipment is multiplied by a disclosed 1.2 / 1.4 / 1.6 markup — the number most calculators hide — and a full change-out adds $1,600–3,600 of labor: one crew day, two techs, 16–24 crew-hours at the $75–150/hr billed rates published in 2026 guides. Billed rates sit well above the $29.33/hr BLS median technician wage; the difference is overhead, insurance, the truck, and margin.
5. Duct work, only if you select it. Sealing and minor repair adds $1,000–3,000; partial replacement of runs adds $2,100–4,000 on a typical home.

What a full change-out costs by home size

Every figure below is computed from the same bands the calculator uses — ducts in good shape, national-average labor, rounded to the nearest $100. The typical column is the mid package (96% AFUE + SEER2 15.2); the full band runs from the standard package's low to the high package's high.

The curve is remarkably flat: more than tripling the home from under 1,000 to 3,400 sq ft raises the typical bill only about 32%. Labor is one crew day either way, the coil and markup structure don't scale with tonnage, and the furnace's BTU class moves its price only ±7–12%. That's why quoting HVAC "by the square foot" flatters small bids and slanders large ones — the fixed costs dominate.

Cost by system type and efficiency

The calculator above prices the most common replacement — a gas furnace paired with a central AC — but "replace the HVAC" can also mean a ducted heat pump or a ductless mini-split system. The table puts the three side by side at the 3-ton / 1,800 sq ft scale. The furnace + AC rows are computed from this page's own bands (list price × disclosed markup + labor); the heat pump and mini-split bands are synthesized from contractor guides published in 2026, so they run wider — equipment mix, electrical scope, and zone count vary far more on those jobs than on a like-for-like change-out.

Read the non-furnace rows as planning bands, not calculator output. A ducted heat pump replaces both boxes at once, so its band overlaps the furnace + AC packages tier for tier — but heating performance (HSPF2) and your electric rate decide whether it wins on operating cost; our heat pump vs. gas furnace guide runs that math in dollars per million BTU. A mini-split system is usually the answer to a different question — no ducts, or ducts too far gone to reuse — and its price scales with zone count rather than tonnage, which is why the whole-home rows climb past a comparable ducted change-out.

The 1,800-square-foot benchmark, worked out loud

Because "how much to replace the HVAC in an 1,800 sq ft house" is the question most people actually have, here is that exact scenario, line by line, at the mid package: a 96% AFUE 80,000 BTU furnace lists at $1,883 and a 3-ton SEER2 15.2 condenser at $3,420, plus a $1,200 matched coil. That $6,503 of equipment becomes about $9,100 after the typical 1.4× contractor markup, and one crew day of change-out labor adds $2,500 — about $11,600 total, inside a planning band of $8,700 to $14,800. Drop to the standard package (80% AFUE + SEER2 14.3) and the typical falls to about $9,800; step up to the high package (97% modulating + two-stage SEER2 17) and it climbs to about $14,400. None of those figures include duct repair — add $1,000–4,000 if your bids flag it.

HVAC replacement cost per square foot

The same default scenario works out to $4.80–$8.20 per square foot of home, with the typical near $6.45. Published planning guides put residential HVAC at $3–6 per square foot for a system, $5,000–11,000 for a change-out, and $7,000–16,000 when ductwork is involved — our standard package sits inside the change-out band, while the mid-package typical lands right at the bottom of the $11,590–14,100 published 2026 market average for a full replacement. The calculator prints your own per-square-foot figure so you can compare a bid the same way. Just remember the flat-curve caveat above: per-square-foot is a sanity check for spotting a wild bid, not a pricing formula, because a 900 sq ft cottage legitimately runs over $11 per square foot while a 3,400 sq ft colonial runs close to $4.

Furnace and AC together, or one at a time?

If only one side of the system has failed, replacing just that side is often reasonable — our AC replacement calculator prices the cooling side alone, and our furnace replacement cost guide works the heating side, including the 80% vs 96% AFUE payback math. But the combined job has real economics behind it: one mobilization, one crew day instead of two, one refrigerant charge, and equipment that is warranty-matched from day one. If the surviving half is past roughly 12–15 years — most furnaces last 15–20, most condensers 12–15 — the odds are you'll pay for a second crew day within a few years anyway. Price both scopes before deciding; the delta is usually smaller than people expect.

One more system-level decision worth making deliberately rather than by default: if you heat with oil, propane, or electric resistance, compare a heat pump before committing to another gas furnace. Our heat pump vs. gas furnace guide runs that operating math in dollars per million BTU.

What can move your real price outside this range

• Regional labor — the BLS wage data behind our labor band ranges from about 20% below the national median in the Gulf South to 25%+ above it in California, New England, and the DC corridor. Coastal-metro bids commonly clear our high band on labor alone.
• Duct surprises — a change-out bid that assumed reuse can grow mid-job if runs turn out crushed or the returns are undersized for the new blower. Our ductwork replacement cost guide prices sealing versus replacement per square foot and per run so you can judge that change order.
• Venting for condensing furnaces — a 96%+ furnace vents through sidewall PVC and drains condensate; if your old 80% unit shared a chimney flue with the water heater, code may require relining or rerouting that flue, which is real money bids handle very differently.
• Refrigerant transition — 2025–2026 is the R-410A to R-32/R-454B changeover: new-refrigerant equipment carried a 3.2% manufacturing price increase in the year to May 2026, and old coils generally can't be reused. Which refrigerant you get follows the brand — R-32 in the Goodman equipment our price anchors use, R-454B at Carrier, Trane, Lennox, Rheem, and York.
• Code and permit items — permits ($50–300), a code-current disconnect, smoke/CO detector requirements, and condensate safety switches. Honest bids itemize them; lean bids discover them later.

Frequently asked questions

How much does it cost to replace an HVAC system in an 1,800 sq ft house?

About $11,600 typical for the mid package — a 96% AFUE furnace with a SEER2 15.2 air conditioner at 3 tons — inside a planning band of roughly $8,700 to $14,800 with ducts in good shape. The standard package (80% AFUE, SEER2 14.3) brings the typical down to about $9,800, and duct sealing or partial replacement adds $1,000 to $4,000 on top of any package.

What does HVAC replacement cost per square foot?

Our 1,800 sq ft default works out to about $4.80 to $8.20 per square foot of home, with the typical near $6.45 — straddling the top of the $3 to $6 per square foot planning benchmark HomeGuide publishes, and landing right at the bottom of the $11,590–14,100 published 2026 market average for a full replacement. Treat per-square-foot as a sanity check, not a pricing rule: labor, the coil, and the markup structure barely scale with home size, so small homes run high per foot and large homes run low.

Is it cheaper to replace the furnace and AC at the same time?

Often, though not automatically. Priced with our own bands, the combined change-out lands within a few hundred dollars of a furnace-only job plus an AC-only job — the real savings are structural: one mobilization, one crew day of labor ($1,600 to $3,600), one refrigerant charge, and equipment that is warranty-matched from day one, where separate projects each carry their own call-out and an aging survivor often fails within a few years anyway. If your furnace is past roughly 12 to 15 years when the AC fails, price both scopes before committing.

Does an HVAC replacement quote include ductwork?

Usually not — most change-out bids assume your ducts stay as they are. If they leak or are undersized, sealing runs about $1,000 to $3,000 and partial replacement of runs adds about $2,100 to $4,000 on a typical home. Skipping needed duct work quietly cancels much of the efficiency you paid for in the new equipment.

Is this a quote?

No. It is a planning range built from published distributor equipment prices, a disclosed contractor markup, and labor data, meant to tell you whether a real bid is in reasonable territory. Get at least three written quotes and ask each bidder to itemize furnace, AC, labor, and duct work the way this page does.