Gas furnace replacement cost calculator (2026)

How this estimate is built

A replacement gas furnace in 2026 starts from an installed base of $3,000–$5,000 for a single-stage 80% AFUE unit and $4,000–$6,500 for a 95–97% condensing unit, where the base already includes the new PVC intake and exhaust run, a condensate drain or pump, labor for a one-day install, gas and electrical reconnection, the permit, startup, and haul-away. Two-stage models with a multi-speed blower add $600–$1,200; fully modulating furnaces with variable-speed ECM blowers add $1,500–$3,000. Size scales the equipment and labor modestly: a 40–60k BTU unit is about 10% below the typical 60–80k band, and 100–120k units about 20% above.

The add-ons are where quotes diverge. An 80% furnace that can't reuse its existing metal vent needs a new one ($400–$1,200). When a high-efficiency furnace stops using the chimney, the water heater that still vents there is "orphaned" and usually needs a stainless chimney liner ($800–$2,000) — a common surprise. A different cabinet size means a new plenum and transitions ($300–$800), and adding a return to fix airflow is $500–$1,500 more. The planner's typical band for a straightforward replacement is $3,500–$7,500; this calculator shows why a real quote can land outside it.

80% or 95%+?

AFUE is the share of the gas that becomes heat in the house. An 80% furnace sends a fifth of your gas bill up a metal flue; a 96% unit recovers most of that but needs PVC venting out a side wall and somewhere to drain the acidic condensate. In a cold climate with a real heating season, the condensing unit usually pays back its premium in 5–10 years; in a mild climate, the simpler 80% install is often the better value, especially where the existing vent and water heater arrangement can stay. Ask each bidder for the estimated annual operating cost of both at your actual gas rate — a good contractor can produce it in a minute.

Single-stage, two-stage, or modulating?

Single-stage furnaces are either off or at full fire; they're reliable and cheapest. Two-stage units run at roughly 65% most of the time and step up only on the coldest days, which means longer, quieter cycles and more even temperatures. Modulating furnaces adjust in small increments and pair with variable-speed blowers for the best comfort and the highest price. Staging improves comfort more than it improves efficiency — if the budget is tight, spend on the AFUE tier and a correct Manual J sizing before you spend on modulation.

Repair or replace?

Under 12 years old with a failed igniter, flame sensor, inducer, or blower motor — repair. Past 15 years, a cracked heat exchanger (not repairable; the furnace is done), a failed control board plus another major part, or repair quotes above about $800 point to replacement. The furnace troubleshooting guide covers what you can check yourself before you call anyone.

Getting quotes

Get three, ideally in September or spring rather than the first cold week. Each quote should name the exact model, AFUE, BTU input, and staging; state whether a Manual J load calculation was done (oversized furnaces short-cycle and wear out early); itemize venting, condensate handling, plenum work, thermostat, and permit; and separate the labor warranty from the manufacturer's parts and heat-exchanger warranty. Ask what commissioning they do — combustion analysis and temperature-rise measurement should be standard. Line the bids up in the quote comparison worksheet.