How much does it cost to replace a gas furnace?
Replacing a gas furnace runs $4,500–$9,000 installed for most homes — the unit itself costs $1,200–$4,500 depending on efficiency tier, and installation adds $1,500–$3,500 in labor. Higher-efficiency furnaces cost more upfront but can save $200–$500 per year in gas compared to a basic model.
The single most important spec on a gas furnace is its AFUE rating — that number tells you what percentage of the gas you pay for actually heats your home. An 80 AFUE furnace wastes 20% up the flue; a 96 AFUE unit wastes only 4%.
Gas furnace tiers — what you get at each price level
80 AFUE — single-stage, standard efficiency
$1,200 – $2,200 unit; $3,500 – $5,500 installedHow to tellEntry-level replacement; meets minimum federal efficiency standard in most of the US (northern climate rules differ)
The fixVents through a standard metal flue — easiest replacement; lower upfront cost but higher operating cost vs higher tiers
90–96 AFUE — two-stage or modulating, mid-efficiency
$2,000 – $3,200 unit; $4,500 – $7,500 installedHow to tellMost popular tier; qualifies for utility rebates in most states; meaningfully lower gas bills than 80 AFUE
The fixRequires PVC flue (vents out a side wall, not up through the roof) — if replacing an 80 AFUE, venting change may add cost
97–98 AFUE — modulating, premium efficiency
$3,000 – $4,500 unit; $6,000 – $9,000 installedHow to tellTop-tier efficiency; modulating gas valve adjusts output in small increments for maximum comfort and fuel savings
The fixHighest upfront cost; best comfort (fewer temperature swings); best payback in climates with harsh winters and high gas prices
Venting change (80→90 AFUE)
Add $200 – $600How to tellUpgrading from 80 AFUE to a 90+ unit requires new PVC side-wall venting — the high-efficiency exhaust is too cool for a metal flue
The fixHVAC tech runs new PVC vent pipes and caps them at an exterior wall; old metal flue gets capped
Duct modifications or air handler upgrade
Add $300 – $1,500 if neededHow to tellNew higher-output furnace may require duct adjustments; some homes need a new air handler if the old one is incompatible
The fixHVAC tech assesses duct sizing — undersized ducts reduce efficiency regardless of furnace quality
Try this first (before you pay anyone)
- Check your filter first — a dirty filter is the #1 cause of furnace short-cycling, tripped limit switches, and apparent failures. Replace it and run the furnace before calling anyone.
- Look at your existing furnace's AFUE rating (on the yellow EnergyGuide label or model number lookup) — if you're replacing, knowing your current efficiency tells you exactly how much you'll save by upgrading.
- Call your gas utility before buying — many offer $100–$400 rebates on qualifying high-efficiency furnaces, and some have contractor partnerships with reduced installation rates.
Unlock the hiring checklist
Use this before you call an hvac, so you know what to ask and what to avoid.
Call a pro when…
- No heat with a heat emergency — call same day; any licensed HVAC company handles emergency furnace calls
- You smell gas anywhere near the furnace — evacuate, call the gas company first, then an HVAC contractor
- A tech quotes 'cracked heat exchanger' — this is a real CO safety issue, but also the most commonly fabricated finding to sell a new furnace; ask for a photo and a second opinion before committing
Repair or replace?
The 50% rule: if the repair quote exceeds 50% of what a new unit would cost, replace. A $1,500 repair on a furnace where replacement runs $5,000 is borderline; if the furnace is under 10 years old, repair. If it's 15+ years old, that money is better applied to a new unit. Heat exchanger failure on a furnace over 15 years old is almost always a replace decision — heat exchangers cost $1,500–$3,000 to replace, and they fail because the furnace is near end of life.
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Related questions
What does AFUE mean in plain language?
AFUE stands for Annual Fuel Utilization Efficiency. It's the percentage of the gas you pay for that actually heats your home. An 80 AFUE furnace converts 80 cents of every dollar of gas into heat and sends 20 cents up the flue as waste heat. A 96 AFUE unit converts 96 cents. If you spend $1,500/year heating a house with an 80 AFUE furnace, a 96 AFUE unit would reduce that to about $1,250 — saving roughly $250 per year.
How long does a gas furnace last?
Most gas furnaces last 15–20 years with annual maintenance. Systems that run without regular filter changes or tune-ups often fail sooner — 12–15 years. Heat exchangers are typically the failure point on older units; if yours is past 18 years, budget for replacement in the next few years even if it's still running.
Is it worth upgrading from 80 to 96 AFUE?
In cold climates (Wisconsin, Minnesota, New England) with high gas prices, the payback on a 96 AFUE upgrade over an 80 AFUE is typically 5–8 years in energy savings. In mild climates with low gas prices, the payback extends to 10–15 years. Utility rebates improve the math significantly — always check before choosing your tier.
Do I need a new furnace if my AC still works?
Usually yes — a gas furnace and central AC are different systems that share the ductwork. Replacing just the furnace doesn't affect the AC unit. If both the furnace and AC are near end of life, replacing them together can save money on labor and get you a matched system that may qualify for better rebates. Ask your HVAC contractor for a combined quote alongside the separate quotes.