Featured brand: Trane
Trane Gas Furnaces: Condensing Efficiency for Spire-Served Missouri Homes
For the majority of St. Louis-metro homes that heat with Spire natural gas, a high-efficiency condensing furnace is the workhorse replacement: it captures heat a standard furnace sends up the flue, converts it in a second heat exchanger, and vents cool exhaust through PVC instead of a hot metal chimney. Trane's condensing lineup, with two-stage and variable-speed blower options, is the version of that workhorse we install and stand behind.
Condensing gas furnaces
What it is
AFUE (Annual Fuel Utilization Efficiency) is the share of your gas bill that becomes heat in the house. The federal floor for new furnaces is 80% AFUE; condensing furnaces run in the 90s, and the difference goes straight to the Spire bill every month of every winter.
The blower matters as much as the burner. A variable-speed blower ramps gently, runs quietly, moves air continuously for filtration and mixing, and holds comfort during long shoulder-season runs. It's also the foundation the whole system stands on if you add a heat pump above it later, a condensing furnace with a variable-speed blower is the natural bottom half of a future dual-fuel system.
Condensing furnaces produce condensate and need proper drainage and venting, retrofit details our installers handle as part of every changeout, along with combustion verification and the permit for your address's Authority Having Jurisdiction.
The efficiency story
AFUE, against the floor and the rebate tiers
Furnace efficiency anchors are unusually clean: a statutory federal floor and Spire's published rebate tiers. Here's the map.
Anchors are the federal minimum and Spire Missouri's published residential rebate tiers. Your exact model's AFUE is on its rating plate and your quote, and Spire's rebate paperwork is something we handle when the equipment qualifies.
Who it fits
Which St. Louis-metro homes this actually serves
Not sure where your house lands? Take the two-minute Which System Fits Your Home walkthrough, it's built on the same honest logic.
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Spire-served homes keeping gas heat
The straightforward replacement path for most of the metro, better efficiency in the same fuel, with rebate tiers to match.
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Homes with 15 to 20+ year furnaces
The 1990s-2000s builder-grade stock across O'Fallon, St. Peters, and Wentzville is aging out, replacing before failure beats replacing during a January emergency.
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Future dual-fuel candidates
A condensing furnace with a variable-speed blower is the right bottom half if you add a heat pump later.
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Comfort-and-quiet upgraders
Two-stage and modulating burners with variable-speed blowers smooth out the blast-and-stop rhythm of old single-stage furnaces.
The honest ledger
Pros, and the considerations the brochure skips
Why homeowners pick it
- + 90s-AFUE efficiency turns wasted flue heat into living-room heat, every winter
- + Spire rebate tiers reward exactly this equipment class
- + Variable-speed blower options improve comfort, filtration, and future heat-pump readiness
- + PVC venting frees old chimney-dependent placements
Worth weighing first
- − Condensate drainage and new venting are real retrofit line items, we scope them in the quote, not as surprises
- − In a tight mechanical closet, venting routes can constrain model choice
- − If your ducts are undersized, the best furnace can't fix airflow, we measure static pressure first
- − 80% AFUE units remain the budget floor; we'll quote one honestly if the venting situation favors it
Savings that may apply
Rebates & incentives for this equipment
Program figures below come from published utility program documents and change by program year, eligibility conditions are real, so we confirm what your project qualifies for before you count on a number. Financing options live on Rebates & Financing .
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Ameren Missouri · Pay As You Save (PAYS)
$250 per thermostatSmart thermostats
ENERGY STAR (or Ameren-approved) smart thermostats carry their own PAYS rebate, an easy add-on when new equipment goes in, and one of the most practical upgrades for part-time and lake homes.
- ENERGY STAR certified or on Ameren's approved list
- PAYS program participation
Amounts and rules come from Ameren Missouri's published 2026 PAYS rebate charts and change by program year, we confirm current eligibility and amounts for your project before you count on a figure. Ameren Missouri PAYS rebates
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Spire · Spire Missouri residential rebates
$200 to $300 by efficiency tierHigh-efficiency gas furnaces
Spire rebates qualifying high-efficiency natural gas furnaces installed by a licensed contractor, $300 for 96%+ AFUE models and $200 for the 92 to 95.99% AFUE tier, with a similar rebate for 90%+ AFUE boilers.
- Active Spire residential account at the installation address
- Installation by a licensed HVAC contractor (self-installs are ineligible)
- Program year runs October 1 through September 30; per-dwelling rebate limits apply
Amounts come from Spire's published Missouri residential rebate application (program year runs October-September) and are subject to program funding, we confirm what's current for your equipment before you count on a figure. Spire rebates
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Spire · Spire Missouri residential rebates
$75 per thermostatSmart thermostats (gas heat)
Spire offers a rebate on ENERGY STAR Wi-Fi smart thermostats for gas-heated homes, stackable thinking: the electric and gas utilities each run their own thermostat programs, and we point you to the one your fuel setup qualifies for.
- ENERGY STAR certified Wi-Fi smart thermostat
- Active Spire residential account
Amounts come from Spire's published Missouri residential rebate application (program year runs October-September) and are subject to program funding, we confirm what's current for your equipment before you count on a figure. Spire rebates
Keep learning
Related guides & comparisons
- Which system fits your home? →
- How furnaces work →
- Furnace lifespan in Missouri →
- Heat pump vs furnace →
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