Missouri HVAC Match
An outdoor air conditioning condenser unit on a concrete pad next to the gray vinyl siding of a residential home.

AC Installation in St. Louis, MO

A new air conditioner in St. Louis will run from May through September every year. Tell us about the house, and a licensed contractor who covers St. Louis will get in touch.

Tell us about the job

It takes about a minute.

Step 1 of 3: Equipment
Overhead view of an air conditioning condenser unit on a concrete pad next to a house with asphalt shingle roofing and vinyl siding.

Five months of St. Louis heat, and the storms in between

Your air conditioner runs May through September here, with afternoons averaging 87°F. That is five months of steady work for the compressor, and the hotter the air outside, the harder it runs to move heat out of your house.

St. Louis also sees hail and wind. The last ten years brought 16 hail events, one with stones 2 inches across, and 28 damaging wind events. The outdoor unit sits outside through all of it, so the cabinet and the coil inside it take the hit. Any new central air conditioner installed today has to meet a federal minimum of 13.4 SEER2, so whatever goes in will meet that baseline for efficiency.

5 months
May through September, your air conditioner is on duty
87°F
the average summer afternoon it cools against
16 hail events
in ten years, and hail bends the fins on outdoor coils
13.4 SEER2
the federal minimum any new unit must meet
Isometric line illustration of a cutaway single-story house showing interior rooms with furniture, ceiling ductwork, an indoor air handler, and an outdoor condenser unit connected by lines along the exterior wall.
Your air conditioner works hardest from June through August.

NOAA nClimDiv, 1991–2020 normals

Overhead view of a gray outdoor AC condenser unit on a concrete pad beside a mulched garden bed and a house with vinyl siding.

A higher-efficiency unit would save about $30 a year to run in St. Louis compared with a new unit at the federal minimum.

  • A higher-efficiency unit$270 a year
  • A new unit at the federal minimum, 13.4 SEER2$300 a year

Estimates for a typical St. Louis home, from EIA household energy data, Missouri fuel prices and NOAA climate normals. Your home will differ.

What size air conditioner does my house need?
There's no single number that fits every house. Sizing comes down to square footage, how many windows you have and which way they face, how much insulation is in the attic and walls, and the layout of your ductwork. A contractor works this out with a load calculation, not a rule of thumb like tons per square foot. Getting it right matters, because a system that's too big cools the air fast but leaves the house feeling damp, and one that's too small runs nonstop and still falls behind on the hottest afternoons.
Should I replace the whole system or just the outdoor unit?
If your outdoor unit is original to the house and the indoor coil and furnace are the same age, replacing just the condenser usually isn't a good idea. The refrigerant and the coil have to match what the new unit needs, and an old coil paired with a new condenser can cause problems or just run poorly. A contractor can check whether your indoor coil is compatible before you decide. If the rest of the system is only a few years old, replacing just the outdoor unit can make sense.
Do HVAC contractors in St. Louis need a state license to work on my home?
Ask any contractor you're considering what license or permit they hold to do this kind of work. A licensed contractor can tell you directly what covers the job and show you the number. That's a fair question to ask before anyone starts work on your system.
Find a contractor