Cost to Install a Gas Furnace

The cost to install a gas furnace is $3,000 to $8,000, installed. A mid-efficiency 80 percent AFUE unit in an easy location sits near the bottom. A 96 percent condensing furnace with new venting and gas work sits near the top.

This guide breaks the job into the furnace, the labor, the venting, and the gas and electrical connections. It also covers efficiency ratings, sizing, and where you can trim the bill.

What It Costs to Install a Gas Furnace

Most homeowners pay $4,000 to $6,500 to install a gas furnace as a like-for-like replacement. The furnace itself is $1,200 to $3,500. Labor is $1,000 to $2,500 for one day.

A cheaper job keeps the same efficiency class, the same location, and the existing venting and gas line. A pricier job upgrades to a condensing furnace, which needs new PVC venting and a condensate drain.

The table below shows installed cost by efficiency. Read the sizing section, because an oversized furnace short-cycles and wears out early.

Brand matters less than the installer. A mid-priced furnace fitted well by a careful contractor outlasts a premium unit rushed in by a low bidder, so weigh the crew and the warranty terms as heavily as the box.

AFUE and Efficiency Classes

Furnace efficiency is rated in AFUE, the percent of fuel turned into heat. An 80 percent unit sends 20 percent up the flue. A 90 to 98 percent condensing unit recovers most of that. The Department of Energy furnace guide explains the ratings in detail.

An 80 percent furnace is cheaper to buy and vents through an existing metal flue. A condensing furnace costs $800 to $2,000 more and needs new PVC intake and exhaust piping plus a drain.

In a mild climate or a home you will sell soon, 80 percent is often the right call. In a cold climate with a long heating season, a 95 percent or higher furnace usually pays back.

Where the Money Goes

The furnace is 30 to 45 percent of the job. Labor is the next largest share, because the work touches gas, venting, electrical, and the duct plenum.

New venting for a condensing furnace is $300 to $1,200. A gas line adjustment is $150 to $600. A new thermostat, a condensate pump, and a permit add $200 to $800 together.

See our HVAC cost guides for the AC and heat pump comparison, since many replacements do both at once.

What Drives the Price Up

Switching efficiency class is the biggest add. Going from an 80 percent to a condensing furnace means new venting, a drain, and sometimes a longer gas run.

An attic or a tight crawlspace location, a furnace that has to be turned to fit a new cabinet, or ductwork that needs a transition all add labor. Upsizing the unit can require a larger gas line and a bigger return.

If the home has no AC and you want it, adding a coil and condenser at the same time is efficient. Our cost to replace a central AC unit guide covers that side.

Furnace Sizing

Furnace output is measured in BTU per hour. A typical home needs 40,000 to 80,000 BTU, but the right number comes from a Manual J load calculation, not the old unit's label.

An oversized furnace heats the air fast, shuts off, and cycles on and off all day. That wears the ignitor and blower, creates temperature swings, and can be noisy.

A right-sized furnace, ideally a two-stage or modulating model, runs longer and gentler cycles and holds a steady temperature. Ask for the load calculation in writing.

Single-Stage, Two-Stage, and Modulating

A single-stage furnace runs at full output or off. It is the cheapest and fine for a small, well-insulated home.

A two-stage furnace has a low and a high setting, so it runs quietly at low most of the time and only ramps up on the coldest days. It costs $300 to $800 more.

A modulating furnace fine-tunes its output continuously and pairs with a variable-speed blower for the steadiest comfort. It costs the most and suits large homes and long, cold winters.

Signs Your Furnace Needs Replacing

Age is the main one. A gas furnace lasts 15 to 25 years. Past 15, a major repair such as a heat exchanger or a control board is usually money on a unit near the end.

A cracked heat exchanger, a yellow or flickering burner flame, soot, or a carbon monoxide alarm mean stop using it and replace it. Rising gas bills, uneven heat, and frequent short cycling point the same way.

If the furnace is old and you are also replacing the AC, doing both together saves a trip and guarantees a matched blower and coil.

Permits, Safety, and Timing

Furnace replacement needs a permit and an inspection. The inspector checks the gas connection, the venting, the combustion air, and the electrical.

Never skip the permit on gas work. A bad vent or gas connection is a carbon monoxide and fire risk, and an unpermitted install can void insurance.

Spring and early fall are the low season. Replacing then costs less and avoids the wait when the first cold snap floods every contractor with no-heat calls.

Regional and Fuel-Cost Differences

Labor rate sets much of the spread between quotes, and it tracks the local cost of living. The same like-for-like furnace swap can be $3,500 in one market and $6,500 in another.

Fuel price shapes the efficiency decision. Where natural gas is cheap, the payback on a 96 percent furnace over an 80 percent model is slow. Where gas is expensive, or you heat with propane, the high-efficiency unit pays back faster.

Cold-climate states also see more code requirements, such as sealed-combustion units and specific venting clearances, which nudge the baseline price up.

What to Expect on Install Day

A like-for-like swap is a one-day job. The crew shuts off the gas and power, removes the old furnace, sets the new cabinet, reconnects the plenum, gas, venting, and wiring, then fires and tests it.

They check the gas pressure, the temperature rise across the heat exchanger, the flame, and the safety limits, and set up the thermostat. A condensing unit also gets its condensate line and trap primed.

The house is without heat for part of the day. In cold weather, ask the crew to start early and confirm they carry the right unit on the truck so there is no overnight gap.

How to Keep the Cost Down

First, get three itemized quotes with the model numbers, the AFUE, and the load calculation. Compare like for like.

Second, replace in the shoulder season. Third, keep the same efficiency class and location if the existing venting and gas line are sound.

Fourth, choose two-stage over modulating unless your climate and home size justify the top tier. Fifth, bundle the AC if it is also near the end.

Bottom Line

Budget $4,000 to $6,500 to install a gas furnace as a like-for-like swap, and $5,500 to $8,000 to move up to a condensing unit with new venting. A basic 80 percent swap in an easy spot can come in under $4,000.

Size it with a load calculation, replace in the shoulder season, and match the efficiency to your climate. If the AC is also aging, price the pair, and consider whether a heat pump should do the heating instead. Keep the ducts sealed and confirm your AC coil matches.