Honest pricing · real ranges, no games
How much does a new furnace cost in the St. Louis area?
Most O'Fallon and St. Louis-metro homeowners invest between $4,000 and $8,000 for an installed gas furnace replacement. A standard 80% AFUE single-stage unit sits at the low end; a 96%+ AFUE variable-speed furnace can reach $9,500. Sizing, venting, and your ductwork set the exact number, which is why honest pricing starts with a free in-home visit.
Typical timeframe: Most furnace swaps: one day, often before the evening cold sets in
No-obligation estimate · Comfort advisors don't work on commission · MO License #M2793A
By configuration
What does each furnace tier cost?
Installed ranges for the O'Fallon / St. Charles County / greater St. Louis area. Your written quote depends on your home, the factors below explain what moves it.
Reliable standard-efficiency heating; metal-vented like most older furnaces
High-efficiency condensing furnace, quieter, steadier heat, lower gas bills
Top-tier comfort: fine-grained flame and blower control, best humidity behavior
For all-electric homes or paired with a heat pump
Ranges are representative 2026 St. Louis-metro estimates, not quotes. Swiss Air confirms your exact price in writing after a free in-home evaluation, and explains every line item before any work begins. Updated July 20, 2026.
What changes the price
What affects your furnace price
Efficiency tier (AFUE)
An 80% AFUE furnace sends about 20 cents of every gas dollar up the flue; a 96% unit keeps nearly all of it as heat. Higher tiers cost more up front and less every winter after.
Venting changes
Condensing (90%+) furnaces vent through PVC and need a condensate drain. Switching from an 80% metal-vented unit adds install scope, a real cost an honest quote itemizes.
Correct sizing (Manual J)
An oversized furnace short-cycles: loud, uneven, hard on parts. Correct sizing comes from a load calculation on your home, not the nameplate of the furnace being replaced.
Blower type and your AC
The furnace blower moves your cooling air too. A variable-speed ECM blower improves summer dehumidification in St. Louis humidity, and matters if your AC is next to be replaced.
Gas line, electrical & access
Tight closets, attic or crawl installs, gas-line updates, and flue routing all move labor time, things no online calculator can see.
Permits & inspection
St. Louis-area jurisdictions require a mechanical permit for furnace replacement. Swiss Air handles the paperwork and inspection as part of the price.
The honest part
Why exact pricing needs a home visit
- Furnace sizing comes from a Manual J load calculation on your actual home, not the old unit's label.
- Venting and condensate routing for high-efficiency furnaces depend on your home's layout.
- Your ductwork and existing AC determine which blower and cabinet actually fit.
- Carbon-monoxide safety checks on the existing flue and heat exchanger require eyes on site.
- We show ranges online and give exact prices in writing after a free evaluation, our comfort advisors don't work on commission.
Seen an AI number?
Chatbots return national averages wearing a local label. They can't run a Manual J, see your ducts, or check your panel. Learn what AI misses, then get a real number.
High-efficiency rebates and monthly payments
Ameren Missouri rebates can apply to qualifying high-efficiency furnaces, and financing turns a replacement into predictable monthly payments. We verify current programs for the exact model in your quote.
Quick answers
Frequently asked
- How much does a furnace cost installed in St. Louis in 2026?
- Most installed gas furnace replacements in the O'Fallon and St. Louis metro run $4,000 to $8,000. A standard 80% AFUE single-stage unit runs $4,000 to $5,500; a 96% two-stage runs $5,500 to $7,500; premium modulating furnaces reach $9,500. Your written quote depends on sizing, venting, and ductwork.
- Is a 96% furnace worth it over an 80% furnace?
- Usually, if you'll own the home for several winters. The 96% tier keeps roughly 16 more cents of every gas dollar as heat, runs quieter, and may qualify for rebates, but it needs PVC venting and a condensate drain, which adds install scope in some homes. We'll price both honestly so you can decide.
- How long does a furnace last in Missouri?
- Typically 15 to 20 years with maintenance. If yours is past 15 and facing a major repair like a heat exchanger or control board, replacement usually wins the math, our furnace lifespan guide and repair-or-replace framework walk through it honestly.
- Can AI or an online calculator price my furnace?
- No, it can only guess. Real furnace pricing depends on load calculation, venting changes, duct condition, and code items that require a site visit. Use AI to learn the vocabulary, then get a written quote, and bring us any number for a free second opinion.
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