How Much Does Furnace Replacement Cost in Missouri?

If your furnace is aging out or has just failed, the first question you're asking is: what is this going to cost? It's a fair question, and the honest answer is that furnace replacement prices vary quite a bit based on what you need. Here's a realistic breakdown for Missouri homeowners — no vague ranges, just the key factors that drive the price and what you should expect to pay.

The Overall Cost Range in Missouri

For most Missouri homes, furnace replacement runs between $3,000 and $7,000, including equipment and installation. A basic 80% efficiency unit in a straightforward installation is at the lower end of that range. A high-efficiency 96–98% AFUE system with variable-speed components and any required modifications to the venting or gas line lands at the higher end.

Very large homes, systems with complex installation requirements, or premium brands can exceed $7,000. Simple replacements in smaller homes using mid-range equipment can come in below $3,500.

Efficiency Rating: The Biggest Price Driver

Furnace efficiency is measured in AFUE — Annual Fuel Utilization Efficiency. The higher the AFUE, the more of the gas you burn becomes heat in your home. Two main tiers are common in Missouri:

80% AFUE (standard efficiency): Less expensive equipment, $1,000–$2,200 for the furnace itself. These units vent through a metal flue (the same as older furnaces), so installation is typically simpler. 20% of the gas burned exits through the flue as waste heat.

90–98% AFUE (high efficiency): More expensive equipment, $1,500–$3,500+ for the furnace. These units pull so much heat out of the combustion process that the exhaust gases are cool enough to vent through PVC pipe. This often requires new venting, which adds to installation cost — but the monthly gas savings can be substantial over time.

ENERGY STAR-certified furnaces must meet minimum efficiency thresholds and may qualify for federal tax credits and utility rebates, which help offset the higher upfront cost.

System Size (BTU Capacity)

Furnaces are sized by BTU output to match the heating load of your home. A properly sized furnace for a 1,500 square foot home in Missouri is a different unit than one for a 3,500 square foot home. Larger capacity units cost more. More importantly, the sizing should be based on a proper load calculation — not just "same as the old one."

If your current furnace is oversized (common in older homes where original installations weren't precisely calculated), a properly sized replacement may actually cost less while also running more efficiently and lasting longer.

Installation Factors That Add to Cost

Equipment cost is only part of the total. Installation variables that affect the price include:

• Venting modifications: Switching from an 80% to a 90%+ AFUE system typically requires new PVC exhaust venting. This can add $200–$600 depending on the run length and access.
• Gas line work: If the gas line serving the furnace needs to be modified or extended, this adds cost and requires a licensed plumber or gas fitter.
• Electrical: New furnaces sometimes require a dedicated circuit or updated wiring.
• Duct modifications: If the existing ductwork doesn't connect cleanly to the new unit, modifications may be needed.
• Removal of old equipment: Most installers include old equipment disposal in their quote; verify this.

Tax Credits and Rebates in 2024–2025

The federal Energy Efficient Home Improvement Credit (Section 25C) offers homeowners up to $600 for qualifying high-efficiency gas furnaces. To qualify, the furnace typically needs a 97% or higher AFUE rating. This credit can be claimed on your federal tax return for the year the equipment is installed.

Several Missouri utility companies also offer rebates for high-efficiency HVAC equipment. Laclede Gas, Ameren Missouri, and others have run rebate programs in recent years — ask your installer or check your utility's website for current offers.

These incentives can meaningfully reduce the net cost of a high-efficiency system and should factor into your decision when comparing 80% versus 96%+ AFUE equipment.

The Repair vs. Replace Math

A common decision rule: multiply the repair cost by the age of the furnace. If the result exceeds $5,000, replacement is likely the better value. This isn't a hard rule, but it captures the logic that a costly repair on an aging system still leaves you with an aging system.

Factor in efficiency too. If you're repairing an old 70% efficiency furnace, you're also choosing to keep paying high gas bills. A new 96% AFUE system might save $300–$600 per year in heating costs. Over 15 years, that adds up to $4,500–$9,000 in fuel savings — a number that belongs in the replacement calculation.

Planning a Furnace Replacement in the St. Charles Area

Getting ahead of a furnace replacement — before the system fails in January — gives you time to make a deliberate decision, compare options, and take advantage of available rebates. Emergency replacements are possible, but they happen under time pressure that isn't ideal for major equipment decisions.

AAA Home Services has been replacing and installing furnaces across St. Charles and all of St. Charles, St. Louis, Lincoln and Warren Counties since 1970. Our technicians do not work on commission, which means the recommendation you get is based on what's right for your home — not on which unit produces the highest margin.

Learn more about our heating services or call (636) 397-3200 to schedule an in-home estimate. You can also request service online. We'll give you a straightforward quote and explain the options clearly so you can make a confident decision.