How Much Does AC Replacement Cost in St. Louis? [2025 Data]

AC replacement costs in St. Louis, Missouri, average $4,335, with costs commonly ranging from $2,689 for smaller units with lower efficiency ratings to over $6,386 for larger, more complex systems. St. Louis has humid summers with average temperatures in the high 80s to low 90s, so a working AC system is essential if you want to avoid feeling sticky and sweaty while relaxing at home.

AC Replacement Cost Factors

AC replacement costs in St. Louis depends on several different factors, from the square footage of the space you want to cool to the type of AC unit you want to the unit’s efficiency rating.

Home Size

The median home size in St. Louis, Missouri, is around 1,700 square feet, which needs 3 tons of AC. Here’s how much you can expect to spend on AC replacement in St. Louis based on the size of your home.

AC Unit Size

Your home needs the right AC unit size to cool your home efficiently. You should consult with an HVAC pro in St. Louis, Missouri, to find the appropriate AC size for your home, but you can estimate your costs with the guide below. Each 400 to 500 square feet of space needs about one ton, or 12,000 British Thermal Units (BTUs) of AC.

Type of AC

AC replacement costs in St. Louis depend on the type of AC you’re replacing. If you replace a central AC system that has existing ductwork with another central AC system, you’ll save on the costs to install new ductwork. However, the cost increases if you switch from ductless options to something with ductwork.

Efficiency (SEER)

The higher the Seasonal Energy Efficiency Ratio, or SEER, of your AC system, the more efficient it will be. This can mean a higher up-front cost for higher SEER units, but that also translates to lower energy bills month after month. The minimum SEER requirement for St. Louis is 14.

HVAC Pro Costs

You may be able to replace a window or portable unit yourself, but if you’re replacing central AC, a ductless system, or another large AC system, you’ll need to secure permits and have the work completed by a licensed, certified pro.

Labor

To replace an AC system, you’ll pay $1,500 to $3,500 in labor costs in low- or medium-cost-of-living areas, including St. Louis. In total, labor makes up 30% to 50% of the total cost to replace your AC.

Permits

St. Louis requires AC replacement to be handled by a city-licensed mechanical contractor as well as a mechanical permit. The county of St. Louis requires a permit, which costs $79 per unit plus additional fees for inspections. Fortunately, your mechanical contractor will be able to schedule inspections and apply for proper permits and can conveniently add permit costs into the project total.

Additional Pros to Consider Hiring

If you’re installing a completely different type of AC system than your previous unit, you may want to consider hiring the following experts:

• Electrician: An electrician can upgrade your electrical panel to properly support an updated AC system, especially if you go from a smaller AC unit to a larger one. Hiring an electrician in St. Louis, Missouri, costs $148 to $466.

• Plumber: Expanding from a window unit to central AC? Make sure you have the proper drainage for a bigger system by hiring a plumber. Hiring a plumber in St. Louis, Missouri, costs $169 to $420.

Does AC Replacement Increase Home Value?

St. Louis summers bring high temperatures and humidity, so a newer AC system is an attractive feature for any home. AC replacement can increase home value in St. Louis by up to 10% and has a 30% or higher ROI.

How Angi Gets Its Cost Data

Home is the most important place on earth, which is why Angi has helped more than 150 million homeowners transform their houses into homes they adore. To help homeowners with their next project, Angi provides readers with the most accurate cost data and upholds strict editorial standards. We survey real Angi customers about their project costs to develop the pricing data you see, so you can make the best decisions for you and your home. We pair this data with research from reputable sources, including the U.S. Bureau of Labor Statistics, academic journals, market studies, and interviews with industry experts—all to ensure our prices reflect real-world projects. 

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