Furnace Replacement Cost in St. Louis: Permits Run $200–$400

A gas furnace replacement in the St. Louis area commonly lands in the mid-four figures, and a local permit guide puts a furnace plus AC project at $5,500–$10,000, so budget around the middle of that band. Equipment, ductwork, labor and permits explain the spread, and rebates can pull your net cost down. A licensed contractor pulls the permit and checks rebate eligibility at the diagnostic visit.

TL;DR:

• Budget roughly $200–$400 for combined mechanical and electrical permits; City of St. Louis lists a $25 application fee and $40 per furnace.
• For a Northern U.S. ENERGY STAR furnace, DOE analysis says lifetime savings justify a price premium up to $1,345 in 2023 dollars.
• Ameren Missouri lists example rebates of $1,200–$1,500 for qualifying efficient natural gas furnace upgrades, but eligibility depends on equipment and replacement conditions.
• Treat 15 years as a guideline: recurring repairs or a large efficiency gap strengthen the replacement case, but age alone does not settle it.

Table of Contents

• What does furnace replacement cost in St. Louis?
• How efficiency and system type change the price
• What pushes your estimate above the base price?
• What do permits and inspections cost in St. Louis?
• Which rebates and incentives lower your net cost?
• How long does a furnace replacement take?
• How do you choose a furnace contractor you can trust?
• Should you repair or replace your furnace?
• Why a licensed local installer protects your budget
• Ready for a furnace estimate with no pressure?
• FAQ
• Sources

What does furnace replacement cost in St. Louis?

Start with the only local range we can point to. A St. Louis permit guide reports that a gas furnace and AC split system runs $5,500–$10,000 installed, depending on equipment and scope. That figure covers both pieces of equipment, so a furnace-only job will sit below it. Treat the range as a planning band, not a quote. Your house, your ductwork and the model you choose decide where you land.

For budgeting, think in three tiers. A like-for-like swap with sound ductwork sits at the low end. A mid-efficiency upgrade with some venting work lands near the middle. A high-efficiency unit paired with duct changes pushes toward the top. We build every written estimate so you can see which tier your home falls into, and we never need to pad the scope to get there.

Here is how the job usually breaks down, as shares of the total rather than fixed dollar amounts:

• Equipment: the largest share, and the part that moves most when you change efficiency level.
• Labor: removal of the old unit, setting the new one, gas and electrical connections, startup and safety checks.
• Permit and inspection: a small slice, but required. The local guide puts combined mechanical and electrical permit costs at roughly $200–$400.
• Disposal and recycling: hauling away the old furnace and any scrap.
• Minor ductwork: transitions, sealing and plenum adjustments so the new unit connects cleanly.

Two quick scenarios show how this plays out. In the first, you replace a 15-year-old gas furnace with a similar model. The ducts are in decent shape, the vent already works, and the job takes time. Your total stays toward the lower part of the band. In the second, you step up to a high-efficiency condensing furnace. Now the crew has to run new PVC venting, handle condensate, and often reshape ductwork that was sized for the old unit. Each of those items adds hours and materials, and the total climbs toward the upper part of the band.

If you want the numbers for your own home, request a replacement estimate and we will write the scope out line by line.

How efficiency and system type change the price

Furnaces are rated by AFUE, which measures how much of the fuel becomes heat for your home. Entry-level units sit around 78% AFUE, mid-efficiency units run 90% to 96%, and the top condensing models push higher. Moving up a tier raises the sticker price, but it also cuts the fuel you burn each winter.

The federal numbers help here. Analysis from the Department of Energy’s FEMP lifecycle guidance found that for the Northern U.S., a region that includes Missouri, an ENERGY STAR-qualified furnace saves money over its life if it costs no more than $1,345 above the less-efficient model, in 2023 dollars.

A Missouri-region ENERGY STAR furnace pays for itself over its lifetime when its price premium stays at or under $1,345 (2023 dollars), according to DOE/FEMP analysis. That gives you a concrete test for any efficiency upgrade a contractor proposes.

ENERGY STAR sets its own AFUE floors, and the program planning specifications apply stricter criteria in the northern region. Ask your installer which tier a quoted model falls into.

Here is how the main options compare:

• Non-condensing, around 78% AFUE: lowest equipment price, simplest venting, highest gas use.
• Mid-efficiency, 90%–96% AFUE: condensing design, plastic venting and a condensate drain, noticeably lower gas bills.
• Top-tier condensing: the highest equipment price, with the biggest drop in annual fuel use.
• Air-source heat pump: a different technology that heats and cools. The same permit guide lists heat pump systems at $7,500–$15,000 before incentives, which generally sits above a gas furnace and AC pairing.
• Electric furnace: often cheaper to install, but electric resistance heat usually costs more to run than gas in a cold winter.

The Department of Energy’s equipment selection fact sheet makes a point worth repeating: judge options by lifecycle cost, meaning equipment, installation, annual operating cost and maintenance together, not by the purchase price alone. If you are weighing a heat pump against a furnace, our heat pump installation team can price both side by side.

What pushes your estimate above the base price?

The unit itself is only part of the bill. Most surprises come from the work around it, so it pays to know what to ask about before you sign.

• Labor and access: a furnace in a tight crawl space or a finished attic takes longer than one in an open basement. Removal, hauling and any extra trades add time.
• Ductwork: ducts sized for an older furnace often need sealing, resizing or partial replacement. In many St. Louis homes, skipping that step costs you performance and can shorten the life of the new unit.
• Venting and condensate: condensing furnaces exhaust through plastic pipe and produce water that has to drain or be pumped out. Older chimney flues may need relining or capping.
• Gas piping: the line may need resizing or a new shutoff to meet current code.
• Electrical: a dedicated circuit, a disconnect, or a thermostat wire swap can all show up on the invoice.
• Disposal: some contractors itemize it, others fold it into labor. Ask which.

Installation quality matters as much as the equipment. A Department of Energy field and laboratory study of furnaces at end of life found a significant gap between rated efficiency and real-world performance, driven by installation issues such as ductwork and fan settings. Paying for proper duct work is not an upsell. It is how you actually get the efficiency printed on the label.

Sizing is the other hidden lever. The Department of Energy’s home heating guide notes that sizing matters as much as efficiency and should rely on a Manual J load calculation. Improving the building envelope can also let you install a smaller, cheaper unit. If you are weighing drafty windows, window film’s effect on energy bills is one place to read up before you size equipment.

Pro Tip: Ask every contractor whether the quote includes a Manual J load calculation. If the answer is a shrug, the unit is being sized by guess, and a guess is how you end up with short-cycling and high bills.

What do permits and inspections cost in St. Louis?

Furnace replacement is permitted work. In the City of St. Louis, mechanical permits are issued to licensed mechanical contractors, and there is a $25 application fee. The permit fee table on the city’s mechanical permit fees page lists furnaces and condensing units at $40 per listed item.

Outside the city limits, St. Louis County’s residential mechanical page explains when mechanical permits apply to residential projects. The same rule holds across our service area: a licensed contractor pulls the permit, not you.

• Mechanical permit: covers the furnace swap itself.
• Electrical permit: may apply if the circuit or disconnect changes.
• Combined budget: the local guide puts mechanical and electrical permits together at about $200–$400.
• Inspection: the inspector checks the finished install, including gas connections, before the permit is signed off.

Skipping the permit is a mistake that follows you. Unpermitted work can create insurance problems and complicate a home sale. We handle the paperwork on every job, so permit costs appear in your written estimate instead of showing up later.

Which rebates and incentives lower your net cost?

Incentives can take a real bite out of the total, which is why we check them at the diagnostic visit. Ameren Missouri publishes its offers in a heating and cooling rebate chart that lists rebate amounts by equipment type, along with efficiency thresholds and conditions tied to existing equipment.

For furnaces specifically, Ameren’s energy efficiency incentives handout shows example rebates of $1,200 to $1,500 for certain high-efficiency natural gas furnace upgrades, plus the program’s eligibility rules.

Ameren Missouri lists $1,200–$1,500 example rebates for certain high-efficiency natural gas furnace upgrades. Whether your project qualifies depends on the replacement scenario and the program’s current rules.

What to check before you count on a rebate:

• Replacement scenario: what you are replacing and what you are replacing it with both matter.
• Efficiency thresholds: the chart ties rebates to rated efficiency, so the model you choose affects eligibility.
• Pay As You Save: Ameren’s PAYS program summary shows that larger incentives often depend on system age, existing fuel type and a usage analysis or program appointment.
• Timing: rules and amounts change, so confirm before you sign.

Rebates are never guaranteed, so we treat them as a possible reduction, not a promise. For a plain-language walkthrough, read our Ameren Missouri rebates guide.

How long does a furnace replacement take?

Most of the calendar time is paperwork and ordering, not the install itself. Here is the usual sequence:

1. Diagnostic visit and estimate: we inspect the system, measure the home and write up the scope.
2. Permit pull: your licensed contractor files for the mechanical permit, and the electrical permit if needed.
3. Equipment lead time: common models are often available quickly, while specialty units can take longer.
4. Install day: removal of the old unit, setting the new furnace, connecting venting, gas and electrical, then startup and safety checks.
5. Inspection and sign-off: the permit closes after the inspector approves the work.

On install day, clear a path to the furnace, move stored items away, and keep pets in a safe room. Have your permit paperwork and rebate forms handy so nothing slows the crew down.

Afterward, keep the permit sign-off and warranty papers together, and schedule a first tune-up so the warranty stays valid. Our maintenance plans make that easy.

How do you choose a furnace contractor you can trust?

A good estimate is specific. A bad one is vague, rushed and light on paper. Use this checklist when you compare bids:

• License and insurance: verify both before anyone enters your home.
• Local references: ask for recent St. Louis-area jobs you can check.
• Written scope: the estimate should name the equipment model, the work included and the permit plan.
• Who pulls the permit: the answer should be the contractor, always.
• What is included: ask whether permit fees and taxes are in the price.
• Warranty: get the length and the coverage in writing, for both parts and labor.
• Rebate check: ask whether they verify eligibility before quoting.
• Ductwork: confirm whether the bid includes duct sealing or modification.

Red flags are easy to spot once you know them:

• A refusal to pull permits.
• A scope that reads like a sentence instead of a list.
• No written warranty.
• Pressure to sign today without a diagnostic visit.

Pro Tip: Get at least two written estimates and line them up item by item. If one bid is far lower, find the missing line, because it is usually the permit, the ductwork or the warranty.

Our furnace replacement page explains how we scope a job, so you can compare it against any other bid.

Should you repair or replace your furnace?

A few small steps can lower what you pay, and one rule of thumb helps you decide when to stop repairing.

• Tune up first: a tune-up can reveal whether the furnace has life left or is quietly failing.
• Fix minor problems: a worn igniter or a clogged filter should not push you into a replacement.
• Schedule smart: installs outside the coldest weeks give you more scheduling choice and less rush.
• Bundle work: if your AC is also aging, doing both at once can save a second trip and a second set of permits.
• Run the replacement test: consider replacing when the unit is older than about 15 years, repairs keep coming back, or the efficiency gap against a new model is large.

That 15-year mark is a guideline, not a law. Our post on when to replace your furnace walks through the three rules we use. Before you assume any savings, confirm the permit and rebate details first.

Why a licensed local installer protects your budget

Most St. Louis homes we visit have the same problem hiding behind the old furnace: ductwork sized for equipment from decades ago. A new high-efficiency unit does not forgive that. The honest fix costs something up front, and it saves you from a loud, short-cycling system later. That is the reason permits and duct review belong in the price, not in the fine print.

Cheap bids tend to cut exactly those items. The number looks great until the missing line shows up as a callback. Compare scope, not just totals, and trust the contractor who explains what is in the price. We offer estimates across St. Louis County and Jefferson County, with transparent diagnostics and no pressure to buy.

— Alan Ricotta

Ready for a furnace estimate with no pressure?

You now know what drives the price, so the next step is seeing the number for your own house. We offer a furnace replacement estimate for homeowners in St. Louis County and Jefferson County, and you decide what happens next.

Here is what the visit covers:

• An inspection of your current furnace, venting and ducts.
• A written scope and price, with every line spelled out.
• Permit guidance, so you know what is filed and what it costs.
• A rebate check against current Ameren Missouri programs.
• A realistic timeline from estimate to finished install.

Book your replacement estimate or see our furnace installation service to start.

FAQ

How often should an HVAC system be replaced?

Most furnaces are worth considering for replacement once they pass roughly 15 years, especially when repairs pile up. Age alone is not the deciding factor. Efficiency, repair history and comfort problems matter just as much.

Is a furnace expensive to fix?

Minor repairs like igniters and sensors usually cost far less than replacement, while major component failures can approach a meaningful share of a new unit’s price. When a repair bill climbs on an old furnace, compare it with the cost of replacing before you spend.

What are the signs of a failing furnace?

Watch for uneven heating, frequent cycling, rising gas bills, strange noises and repeated repairs. A yellow or flickering burner flame or any hint of carbon monoxide means you should shut the system off and call for service right away.

Does furnace replacement cost in Missouri include permits?

Not always, which is why you should ask. Mechanical permits are required for furnace replacement, and the City of St. Louis fee page lists furnaces at $40 per listed item. A good written estimate states whether permit fees are included.

Can rebates lower my furnace replacement cost?

They can, but only when your project meets the program rules. Ameren Missouri ties rebates to equipment type, efficiency and replacement scenario, so we verify eligibility before you commit.

Sources

• Complete Guide to HVAC Permits in St Louis, MO (2026)
• Purchasing Energy-Efficient Residential Furnaces | Department of Energy

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• 3 Rules for St. Louis Homeowners: When to Replace Your Furnace