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HVAC · St. Louis, MO · 2026 cost guide
How much does AC replacement cost in St. Louis, MO?
In the St. Louis, MO-IL area, replacing a central air conditioner runs about $5,800 to $12,600 installed in 2026, close to the national range. Contractor labor here is indexed at 1.05 against the U.S. average, and that is what moves the numbers; equipment and materials cost about the same everywhere.
- Central AC
- $5,800–$12,600condenser and coil, installed
- Heat pump
- $7,400–$16,800heats and cools, installed
- AC + furnace
- $9,500–$21,000full split system
- Ductless mini-split
- $4,200–$14,700one to four zones
Replacing an air conditioner in St. Louis costs $5,800 to $12,600 installed for most homes, and the furnace usually comes into the conversation. St. Louis sits in zone 4A with about 1,700 cooling degree days and 4,600 heating degree days, so the AC and the gas furnace both do real work. With gas furnaces dominant and Ameren Missouri's electricity at about $0.14 per kWh, the common upgrade here is a matched AC and furnace or a dual-fuel heat pump, sized for humid summer heat.
What's different in St. Louis
Size for July, not for square footage. St. Louis summers are hot and humid, so the load calculation should account for latent moisture, and an oversized unit that short-cycles leaves the house sticky. Older brick homes are the local complication: masonry walls hold heat into the evening, and the retrofitted ductwork is often undersized, so a Manual J plus a duct static pressure test should be part of every bid. Two-stage or variable-speed equipment runs longer cycles that pull more humidity out and copes better with leaky ducts.
The furnace question comes next. Gas furnaces dominate St. Louis heating, and many are the same age as the AC, so replacing both together saves a second labor charge and gets a matched system. A dual-fuel heat pump makes sense too: with Ameren Missouri's rate at about $0.14 per kWh, the heat pump handles the mild part of the roughly 4,600 heating degree days and the furnace takes the hard freezes. Ameren has offered residential HVAC rebates through its efficiency programs; ask each installer what is currently open for your address and whether the Ameren Illinois programs differ on the Metro East side.
Missouri is in the federal North region, so the floor for a new split AC is 13.4 SEER2; most St. Louis installers quote 15 to 17 SEER2 as the practical range. Permits come from St. Louis City, St. Louis County, or St. Charles County, and from the Illinois county offices on the Metro East side; the installer should pull them and schedule the inspection. Hail is a siting issue: put the condenser where it is not under a roof edge that sheds ice and hail, consider a hail guard on the coil, and keep it above grade in low-lying areas near the rivers where spring flooding is possible.
AC Replacement prices in St. Louis vs. the national guide
These are the ranges from our national AC replacement cost guide next to the same items scaled by the St. Louis, MO labor index of 1.05. Rows marked fixed are materials only and do not move with local labor.
| Item | National range | St. Louis, MO |
|---|---|---|
| Central AC | $5,500–$12,000 | $5,800–$12,600 |
| Heat pump | $7,000–$16,000 | $7,400–$16,800 |
| AC + furnace | $9,000–$20,000 | $9,500–$21,000 |
| Ductless mini-split | $4,000–$14,000 | $4,200–$14,700 |
Local tip: Get St. Louis AC bids in April or October and ask for a combined furnace-and-AC price at the same time; the second labor charge you avoid is bigger than any seasonal discount.
St. Louis at a glance
- Climate zone
- 4Amixed-humid
- Labor index
- 1.05vs. U.S. average 1.00
- Cooling degree days
- 1,700per year, base 65 °F
- Heating degree days
- 4,600per year, base 65 °F
- Min. AC efficiency
- 13.4 SEER2federal minimum for this region
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Should I replace my furnace and AC together in St. Louis?
If the furnace is past about 15 years, usually yes. St. Louis furnaces run through roughly 4,600 heating degree days a year and age as fast as the AC does, and doing both at once means one labor charge, a matched coil and blower, and one permit. If the furnace is under ten years old, a new AC or a dual-fuel heat pump that uses the existing furnace is the better spend.
What SEER2 rating is required in Missouri?
Missouri is in the federal North region, so a new split-system air conditioner must be at least 13.4 SEER2. With about 1,700 cooling degree days, St. Louis has enough summer to justify stepping up to 15 to 17 SEER2 with a variable-speed blower for humidity control, but the very high SEER2 tiers take a long time to pay back at Ameren's rate of about $0.14 per kWh.
Are there Ameren rebates for a new AC or heat pump in St. Louis?
Ameren Missouri has run residential efficiency rebates for high-efficiency AC and heat pumps in past program years, and Ameren Illinois runs its own programs for Metro East customers. Program budgets open and close, so ask each installer what is currently available for your address and who files the paperwork. No federal credit applies to equipment installed in 2026.
How do I protect a new AC from hail in St. Louis?
Site it away from roof edges where hail and ice slide off, ask the installer about a hail guard or fin protector for the condenser coil, and keep it off the ground on a raised pad in low areas near the rivers. Note the serial number and take photos at install, since hail-dented fins on a new unit are usually an insurance matter rather than a warranty one.
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