Understanding your result
The headline is the installed price range, with the midpoint and the furnace described in the sub-line. The stats give the low, midpoint and high. The table shows the furnace installed, the condensing venting and drain, the gas line and the permit as separate lines, then the total and the sources.
The venting line appears only for a condensing furnace replacing an 80% one, and it is often the line missing from a low quote. If a quote for a condensing furnace does not mention PVC venting, a condensate drain or what happens to the water heater’s venting, ask before signing; the notes explain the orphaned water heater problem.
The input size should come from a heating load, not from the old furnace; the furnace size calculator gives a first estimate. The upgrade payback calculator shows whether the condensing premium pays back on your bill, the replacement cost calculator prices a furnace and air conditioner together, and the heat pump installation cost calculator prices the alternative.
How we calculate this
The tier ranges reflect the 2025 and 2026 furnace guides named in the result: a contractor’s price list of $4,400 to $6,200 for an 80% single-stage straight replacement and $6,600 to $9,300 for a 96% two-stage unit, national ranges of $3,500 to $8,500, and premiums of $1,000 to $3,000 for 96% over 80%. The fuel and size factors are our multipliers, set out here so they can be checked. The venting range covers PVC intake and exhaust and a condensate drain; the gas-line range is our estimate from plumbing cost guides. The AFUE tiers and the federal minimums are on the efficiency ratings table.
The assumptions behind the numbers
| Assumption | Value | Where it comes from |
|---|---|---|
| 80% single stage | $3,000 to $6,000 | 2025–26 furnace guides (contractor list $4,400 to $6,200; national $3,500 to $8,500) |
| 95 to 96% two stage | $4,500 to $8,500 | Same guides (96% two-stage $6,600 to $9,300; premium $1,000 to $3,000) |
| 97 to 98% modulating | $6,000 to $10,500 | Same guides, upper range (our estimate) |
| Condensing venting and drain | $500 to $1,500 | Furnace guides’ venting allowances |
| Gas line | $300 to $1,000 | Our estimate from plumbing cost guides |
| Fuel factors | 1.0 / 1.03 / 1.3 / 0.65 | Our multipliers |
| Size factor | ±4% per 20,000 BTU | Our multiplier from equipment price lists |
| Permit | $250 to $500 | Typical mechanical permit (our range) |
Assumptions last reviewed October 8, 2026.
The calculator does not include a chimney liner for an orphaned water heater, a new air conditioner coil (often replaced at the same time), ductwork, a new thermostat, or rebates. In northern states, a 2028 federal standard is expected to make condensing furnaces the norm, which may change the price of 80% units. The guide to furnace input, output and AFUE explains the ratings, and the guide to what HVAC installations cost compares furnaces with the other systems.
Two worked examples
A condensing furnace replacing an 80% unit
80,000 BTU natural gas, 95 to 96% two stage, switching from 80% (new venting), no new gas line, average-cost area, permit.
- Furnace installed: $4,500 to $8,500
- Venting and drain: $500 to $1,500
- Permit: $250 to $500
- Total: $5,250 to $10,500, midpoint $7,875
About $1,000 of the midpoint is the venting change, which a straight 80% replacement would not need. The note about the water heater applies: if it shares the chimney, budget for a liner as well.
An 80% furnace in a lower-cost area
60,000 BTU natural gas, 80% single stage, straight replacement, average gas line, lower-cost area, permit.
- Furnace installed: $3,000 to $6,000 × 0.96 × 0.85 = $2,448 to $4,896
- Permit: $250 to $500
- Total: $2,650 to $5,400, midpoint $4,025
An 80% furnace is the cheapest choice in a mild climate, where a condensing unit’s saving on a small heating bill would take decades to pay back. In northern states the standard is moving towards condensing furnaces, so check what your area allows.
Where to find your inputs
Fuel and size. From the old furnace’s nameplate (input BTU/hr) or the furnace size calculator. Size by the heat loss, not the old label.
Efficiency. From the quote; 80% furnaces vent into a metal flue or chimney, 90%+ furnaces vent through PVC pipe.
Venting change. Tick it when going from a metal-flue furnace to a PVC-vented one.
Gas line. Tick it if the furnace is moving or the existing line is too small for the new unit.
Common mistakes
- Comparing an 80% quote with a 96% quote without the venting. The venting is part of the condensing price.
- Ignoring the water heater. An orphaned water heater may need a chimney liner.
- Replacing like for like on size. Check the heat loss; many old furnaces are oversized.
- Buying condensing in a mild climate for the bill alone. The payback may exceed the furnace’s life.
- Skipping the permit. Gas and venting work should be inspected.
- Forgetting the coil. If the air conditioner is old, replacing the coil now may save a second visit.
Questions people ask
- How much does a new gas furnace cost installed?
- An 80% single-stage gas furnace costs about $3,000 to $6,000 installed and a 95 to 96% two-stage condensing furnace about $4,500 to $8,500, in line with 2025 and 2026 guides that give a national range of about $3,500 to $8,500 and an average near $5,500. Converting from an 80% to a condensing furnace adds about $500 to $1,500 for venting and the condensate drain, and a permit $250 to $500.
- Is a high-efficiency furnace worth the extra cost?
- In cold climates, usually. The premium for a 96% furnace over an 80% one is about $1,000 to $3,000 including venting, and it cuts gas use by about 17%. On a $1,400 heating bill that saves about $233 a year, a payback of six to eight years on equipment that lasts 15 to 20. In mild climates with a $500 heating bill, the payback stretches past the furnace's life. The upgrade payback calculator does the arithmetic with your bill.
- What is an orphaned water heater?
- A gas water heater left alone in a chimney that was sized for a furnace and a water heater together. When the furnace is replaced with a condensing unit vented through the wall, the chimney is too large and too cold for the water heater's small exhaust, which can condense inside it and fail to draft, a carbon monoxide risk. The usual fix is a chimney liner sized for the water heater, typically $500 to $1,500.
- How much does an electric furnace cost?
- Less to install than a gas furnace, because there is no venting or gas line; the calculator uses about 65% of the gas furnace price, our estimate from the difference in equipment and labour. But resistance heat costs about three times as much per BTU to run as gas or a heat pump. If the house has no gas, a heat pump with electric backup usually costs more up front and far less every winter.
- Does furnace size change the price much?
- Less than people expect. The calculator adds or removes about 4% for each 20,000 BTU step from an 80,000 BTU furnace, our estimate from equipment price lists, because the cabinet, controls, labour and venting barely change. The bigger cost of a wrong size is in comfort and wear; an oversized furnace short-cycles. The furnace size calculator estimates the right input.
- Do oil furnaces cost more to install?
- Yes, by about a third in the calculator's estimate, because oil furnaces are built heavier, need an oil line and filter, a chimney or a power vent, and fewer contractors install them. Many households replacing an old oil furnace compare a new oil unit with a heat pump, since heating oil costs about twice as much per BTU as natural gas at 2025 prices.