HVAC Replacement Cost in St. Louis, MO (2026 Pricing Guide)

Why sizing matters more here than the sticker price

St. Louis's humid continental climate means equipment has to handle both a real heating load in winter and a real cooling and dehumidifying load in summer, so a system sized off square footage alone often underperforms.

A proper load calculation, sometimes called a Manual J calculation, accounts for insulation, window exposure, ceiling height, and duct condition, not just the home's total square footage, and this matters especially in older homes that have been added onto or partially renovated.

An oversized AC unit cools the air quickly without running long enough to remove humidity, which is a common complaint in St. Louis summers even when the temperature reading looks correct.

Ask any contractor bidding a replacement to show you the load calculation, not just a quote based on matching the tonnage of your old unit.

A load calculation also accounts for whether ductwork will be retrofitted or a ductless system chosen instead, since duct losses, or the absence of ducts entirely, change the effective capacity needed at the equipment itself compared with the raw room-by-room heating and cooling load.

Furnace and boiler replacement in older homes

Many St. Louis homes, especially brick flats and bungalows in South City and North St. Louis, still run on a boiler and radiator system rather than forced-air. Replacing a boiler is a different job and cost profile than replacing a furnace, since it involves the boiler unit itself plus any needed piping or radiator work.

If a home has forced-air heat already, replacing the furnace is usually simpler and more standardized in cost, especially if the AC is being matched at the same time so both components are sized to work together.

Homeowners considering switching from a boiler to forced-air heat, in order to gain ductwork that also supports central air, should budget for a significant jump in project scope and cost compared with a like-for-like boiler replacement, since it typically requires new ducts throughout the home.

Boiler replacement pricing depends heavily on whether the existing piping and radiators are being reused or need work themselves; a straightforward boiler swap that reuses sound piping is far less disruptive and less expensive than one where corroded piping or failing radiators need attention at the same time.

Ductwork and ductless options for homes without ducts

A large share of older St. Louis housing stock was never built with ductwork, so adding central air means either retrofitting ducts through closets, dropped ceilings, or a new mechanical chase, or choosing a ductless mini-split system that avoids ducts entirely.

Ductwork retrofits are highly dependent on the home's specific layout and can vary a lot in price between two seemingly similar houses, so an in-person assessment is essential rather than a phone estimate.

Ductless mini-split systems avoid the invasive retrofit but do put visible indoor units on walls or ceilings in each zone, which is a tradeoff some homeowners weigh against the disruption of adding ducts.

A contractor experienced with St. Louis's older brick housing stock specifically should be able to walk through both options with real cost estimates rather than defaulting straight to one approach.

Humidity control is a real factor in choosing between the two: a correctly sized ducted central AC system with proper airflow removes humidity effectively across the whole home, while a ductless system's dehumidification is zone by zone, which can work well in homes where only certain rooms need conditioning but requires more units to cover a whole house evenly.

Some homeowners split the difference by ducting the main living areas, where running ducts through a basement or attic is straightforward, and using ductless heads for upper-floor bedrooms in a brick two-story where running ducts through finished walls would be far more invasive.

Equipment tiers and efficiency ratings

Standard-efficiency equipment costs less upfront and is a reasonable choice for homeowners planning to stay in a home only a few more years or working with a tighter budget.

Mid-tier and high-efficiency furnaces and AC units cost more initially but lower monthly utility bills over St. Louis's long cooling season and cold winter months, and may qualify for federal tax credits when the equipment meets efficiency thresholds 1.

Heat pumps, which handle both heating and cooling from one system, are worth considering for homeowners who already have or are adding ductwork, since a modern heat pump can cover most of the year's heating load in St. Louis's climate with a furnace or auxiliary heat as backup on the coldest days.

Whatever tier you choose, get the efficiency rating and specific model number in writing on your bid, not just a general description like "high efficiency," so you can compare bids on equal terms.

Higher-efficiency heat pumps and central air conditioners are also the equipment most likely to qualify for an Ameren Missouri Heating and Cooling Program rebate, and higher-efficiency furnaces and boilers are the ones most likely to qualify for a Spire high-efficiency rebate, so ask your contractor to check both the SEER2 or AFUE rating against current program requirements before finalizing a tier.

Heat pumps in particular are worth pricing against a furnace-plus-AC combination in St. Louis's climate, since a cold-climate heat pump can now cover most winter days here, with a furnace or electric strip heat handling only the coldest stretches, though the right choice depends on your home's insulation, ductwork, and how the household weighs upfront cost against long-term utility bills.

Permits and next steps

Most full furnace, boiler, or AC replacements require a mechanical permit from the correct jurisdiction, either the City of St. Louis Building Division or the St. Louis County Board of Examiners for Mechanical Licensing, so confirm that's included in your bid.

Get two or three bids on the same defined scope, including equipment models and whether ductwork will be added or modified, before deciding, and see how to choose an HVAC contractor in St. Louis for a full breakdown of what to compare.

If you're ready to get quotes from vetted local companies, you can get matched with HVAC pros near St. Louis and compare real bids side by side.

Ask whether your chosen equipment qualifies for a manufacturer rebate, an Ameren Missouri or Spire utility rebate, or a federal tax credit, and get the specific dollar figures and program names in writing rather than a general promise, since stacking eligible incentives can meaningfully change the net cost of a full replacement.

Financing and rebates worth checking before you commit

Ameren Missouri electric customers replacing a central air conditioner, air-source heat pump, or ductless mini-split system with qualifying high-efficiency equipment may be eligible for a rebate through the Ameren Missouri Heating and Cooling Program, with the rebate amount scaled to the equipment's SEER2 rating and what it is replacing.

Spire natural gas customers installing a qualifying high-efficiency furnace or boiler may be eligible for a separate rebate through Spire's residential high-efficiency rebate program, which requires installation by a licensed contractor and an active Spire account at the property.

Qualifying high-efficiency equipment may also be eligible for a federal tax credit; check current ENERGY STAR program details for the specific efficiency thresholds and credit amounts before finalizing your equipment choice.

Because rebate eligibility is tied to specific efficiency ratings and program rules that change periodically, ask your contractor to confirm current eligibility for the exact model being quoted rather than relying on a rebate figure from a prior year, and keep the AHRI certificate and dated invoice on hand in case documentation is needed for a rebate or tax credit filing.

Timing your replacement around St. Louis's seasons

Scheduling a non-emergency replacement in spring or fall, rather than during a July heat wave or a January cold snap, generally means more installer availability, more time for a proper load calculation, and less pressure to accept the first available appointment slot.

If your current system is still functioning but showing its age, planning ahead also gives you time to compare Ameren Missouri and Spire rebate eligibility across a few equipment tiers rather than making a rushed decision when a breakdown forces the issue.

For help comparing contractors once you're ready to get bids, see how to choose an HVAC contractor in St. Louis, and for the full picture on local licensing and permits, see the St. Louis HVAC hub.

Typical cost ranges

Ranges are general estimates gathered from homeowner-reported quotes, not an offer or a quote for your project.

Common questions

More on this market

Local cost ranges, seasons, permits and licensing for this city live on the market page.

Sources

• ENERGY STAR Federal Tax Credits
• City of St. Louis - STL City Permits Online Portal (Building Division, Mechanical Section)
• National Weather Service St. Louis
• Ameren Missouri Heating and Cooling Program (HVAC Pays)
• Spire Missouri Natural Gas Furnace Rebates

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