Furnace Installation Cost Calculator
Furnace Installation costs $2,375 to $3,575 for a typical 1,800 sq ft job in 2026, against a national benchmark of $2,875. Labor runs 9.4 crew hours at $42.44 an hour. Enter a ZIP code to apply that area's measured wages for this work and its regional price level.
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What makes up the price
Cost by size
National averages, before any local adjustment. Computed from the same model as the calculator above, so the two always agree.
| Home size | Thousand BTU | Typical | Range |
|---|---|---|---|
| 1,000 sq ft | 40 | $2,425 | $2,000 to $3,025 |
| 1,450 sq ft | 60 | $2,725 | $2,250 to $3,400 |
| 1,800 sq ft | 70 | $2,875 | $2,375 to $3,575 |
| 2,450 sq ft | 100 | $3,350 | $2,750 to $4,150 |
| 3,050 sq ft | 120 | $3,650 | $2,975 to $4,525 |
80% or 96%, which is the whole decision
Everything else on this page is secondary. The gap is around $1,750 on a typical job, and whether it is worth paying is arithmetic rather than opinion.
What the numbers mean
AFUE is the share of the fuel that becomes heat in the house. An 80% furnace sends a fifth of what you buy up the flue; a 96% furnace sends four percent. So a condensing furnace uses about 17% less gas for the same heat.
Doing the arithmetic
Take your winter gas bills, subtract what you spend in summer — that part is water heating and cooking, not space heating — and multiply the difference by 0.17. That is the annual saving.
| Annual heating gas | Saving at 17% | Payback on $1,750 |
|---|---|---|
| $600 | $102 | 17 years |
| $1,000 | $170 | 10 years |
| $1,600 | $272 | 6 years |
| $2,400 | $408 | 4 years |
A furnace lasts 15 to 20 years. So the condensing unit is clearly right in a cold climate with a real heating bill, clearly wrong in a mild one, and a judgment call in the middle — where comfort, resale and whether you are staying matter more than the arithmetic.
Where the choice is made for you
- No usable flue. If the old chimney is shared with a water heater and the furnace is coming off it, the flue may be oversized for the water heater alone, which forces a liner or a condensing furnace anyway.
- No wall to vent through. A condensing furnace needs a PVC run to an exterior wall and a condensate drain. In some basements and most interior closets that is awkward and occasionally impossible.
- Local code. A few jurisdictions now require 90%+ on replacement.
Why a condensing furnace costs more to fit, not just to buy
The unit is around $1,100 more. The rest of the gap is work:
- PVC venting through a wall, in two pipes — intake and exhaust — rather than connecting to the existing metal flue.
- A condensate drain, because a furnace that extracts that much heat produces water, and that water is acidic. It needs a drain, usually a neutralizer, and sometimes a pump.
- The old flue, which may now be oversized for whatever is left on it.
That is roughly three extra hours and it is why a quote for a 96% furnace is not simply the price difference between two boxes.
Sizing, where bigger is worse
The most common error in residential furnace replacement is fitting a bigger one than the house needs, usually by matching whatever was there before — which was itself oversized.
An oversized furnace short-cycles: it reaches the thermostat setting fast, shuts off, and starts again a few minutes later. The result is:
- Temperature swings and cold spots, because the air never circulates long enough to even out
- More wear on the igniter, the inducer and the heat exchanger, which fail on cycles rather than hours
- Worse humidity control
- No fuel saving at all from the extra capacity
The rule of thumb this calculator uses is 40 BTU per square foot, which suits a moderate climate — it is nearer 30 in the deep south and 55 in the far north. A Manual J load calculation is the proper answer and accounts for insulation, windows, air sealing and orientation. Any contractor proposing a size without one is guessing, and the guess is almost always high.
The ductwork
A furnace is only as good as what distributes its air, and duct problems are invisible.
Leaky ducts in an unconditioned attic or crawlspace can lose 20 to 30% of what the furnace produces before it reaches a room. Sealing them is cheap relative to the furnace and often does more for comfort than the efficiency upgrade does.
Worth asking: are the ducts tested, sealed or simply reconnected to the new unit?
What a replacement should include
- Removal and disposal of the old furnace.
- New plenum transitions — the sheet metal between the furnace and the ducts. Reusing badly fitting ones is a common corner to cut.
- A new flexible gas connector and shutoff.
- A thermostat, and whether it is a basic one or a programmable one.
- Commissioning: gas pressure checked, temperature rise measured against the data plate, combustion analyzed. This is what turns an installed furnace into a correctly running one and is the step most often skipped.
- The permit and the inspection.
Timing
Furnaces fail in the first cold week, which is the worst week to buy one. If yours is over 15 years old, has needed a repair in the last two winters, or has any sign of a cracked heat exchanger, replacing it in spring or early fall is both cheaper and calmer.
An emergency replacement in January costs more and is chosen from whatever is on the truck.
Questions worth asking
- Has a Manual J been done, and what size did it call for?
- 80% or 96%, and what is my actual annual heating gas spend?
- Where does a condensing furnace vent and drain in this house?
- Are the ducts being tested or sealed?
- Is commissioning included — gas pressure, temperature rise, combustion analysis?
- What happens to the water heater's flue if the furnace comes off the shared chimney?
Common questions
How much does a new furnace cost installed?
Around $2,925 for an 80% AFUE furnace in an 1,800 square foot home, with most jobs falling between $2,400 and $3,625. A 96% condensing furnace in the same house is closer to $4,650. New ductwork roughly doubles either figure.
Is a 96% AFUE furnace worth the extra cost?
It depends on your heating bill, and the arithmetic is quick. A condensing furnace uses about 17% less gas, so take your winter gas spend, subtract your summer spend, and multiply the difference by 0.17. Against a gap of roughly $1,750 that is a 4 year payback at $2,400 a year of heating gas and a 17 year payback at $600. A furnace lasts 15 to 20 years, so it is clearly right in a cold climate and clearly wrong in a mild one.
Why does a high-efficiency furnace cost more to install?
Because it is a different machine, not a better grade of the same one. It vents in PVC through an exterior wall rather than into the existing metal flue, and it produces acidic condensate that needs a drain, usually a neutralizer and sometimes a pump. That is around three extra hours of work on top of roughly $1,100 more for the unit.
What size furnace do I need?
Around 40 BTU per square foot in a moderate climate — nearer 30 in the deep south and 55 in the far north — so an 1,800 square foot house lands near 70,000 BTU. That is a rule of thumb. A Manual J load calculation is the proper answer and accounts for insulation, windows and air sealing. Any contractor sizing a furnace without one is guessing, and the guess is almost always high.
Is a bigger furnace better?
No, and this is the most common error in residential replacement. An oversized furnace short-cycles: it hits the thermostat setting quickly, shuts off and restarts minutes later. That gives temperature swings and cold spots because the air never circulates long enough to even out, wears the igniter and inducer faster since those fail on cycles rather than hours, and saves no fuel whatsoever.
How long does a furnace last?
Fifteen to twenty years for a gas furnace, and less if it was oversized and has been short-cycling its whole life. What usually ends it is the heat exchanger cracking, which is a safety matter rather than an efficiency one and is not worth repairing on an old unit.
When is the best time to replace a furnace?
Spring or early fall. Furnaces fail in the first cold week of the year, which is the most expensive week to buy one and the week you choose from whatever is on the truck. If yours is over fifteen years old or has needed a repair in either of the last two winters, replacing it on your own schedule is both cheaper and calmer.
Should I replace the furnace and the air conditioner together?
Often, because they share the indoor cabinet and the ductwork, and doing both at once saves a second set of labor. It matters most if the systems are of similar age or if the new equipment needs a matched blower to reach its rated efficiency. If one has years left in it, there is no technical reason to replace it early.
Do leaky ducts matter?
A great deal, and they are invisible. Ducts running through an unconditioned attic or crawlspace commonly lose 20 to 30% of what the furnace produces before it reaches a room. Sealing them is cheap next to the furnace itself and frequently does more for comfort than upgrading the efficiency does.
What is commissioning and why does it matter?
Checking the gas pressure, measuring the temperature rise against the data plate and analyzing the combustion once the furnace is running. It is what turns an installed furnace into a correctly running one, it takes under an hour, and it is the step most often skipped. A furnace left outside its rated temperature rise is both less efficient and harder on its own heat exchanger.
Where these numbers come from
Nothing here is copied from a contractor directory. Labor is priced from what the trades are actually paid, materials from published producer prices, and both are adjusted to your area using federal cost-of-living data.
- Plumbing, heating and air-conditioning contractors, United States: $42.44/hour, August 2026 (BLS CES CES2023822003)
- Gas furnace, base unit (80% AFUE): $250.00 per furnace (price recorded October 2026, not index-adjusted)
- Gas furnace, capacity (80% AFUE): $10.00 per thousand BTU (price recorded October 2026, not index-adjusted)
- Venting, gas connection, thermostat and filter rack: $280.00 per furnace (price recorded October 2026, not index-adjusted)