Ductless Mini Split Installation in St. Louis, MO

A ductless mini split cools or heats a room with no ducts, using one outdoor unit and a wall-mounted indoor head joined by a small bundle of lines. It is the practical answer when ducts do not exist, cannot fit, or would cost more than the room is worth. It is not the cheapest way to cool a whole house that already has good ducts.

When does a ductless system beat ducts?

A mini split wins where ductwork would be costly or intrusive. Three situations come up most often in St. Louis.

• Brick homes built for radiators. Plaster walls and tight chases leave no path for a retrofit duct system.
• Additions and garages. A new room often exceeds what the existing central system can serve.
• Rooms that never match the rest. A sunroom or third-floor bedroom may need its own zone.

Signs a room needs its own ductless zone

A window unit that runs all summer, a space heater in a finished attic and a bedroom with no register at all are the usual signs. So is any room the central system has never reached. In St. Louis the cause is often the house itself: the median home in the City was built in 1938 (ACS via Neilsberg), and in University City 38 percent of units date to 1939 or earlier (ACS 2020-2024). Those houses were built around radiators and plaster, with no attic runs. Adding ducts means opening finished walls, which is why one head on an outside wall often costs less than the retrofit.

Where good ducts already serve the house, a central system usually costs less per cooled square foot. Our AC installation page covers that route.

Which mini split layout fits your rooms?

The choice is among a few configurations, each with a trade-off.

A heat pump model heats as well as cools. See heat pump installation for how that compares with a furnace.

What a ductless installation includes

A mini split installation covers the design, the hardware and the hookup, and the quote should list each part by name. Ask for model numbers, because the head and the outdoor unit must be a matched set. Anything excluded, such as electrical work or patching, should be marked excluded. The core scope:

• A room-by-room load calculation and a head placement plan
• Indoor head or heads and the outdoor heat pump unit, with model numbers
• Line set, drain and control wire, with one sealed wall penetration per run
• A pad or wall brackets for the outdoor unit
• A dedicated circuit and disconnect, with who does the electrical work stated
• A permit plan, evacuation of the lines and a heating and cooling test

How do you size and place the indoor heads?

Each head is sized to the load of its room, not the house, using a room-by-room load calculation. Oversizing short-cycles a unit and leaves the room damp. Placement matters as much as size: high on an exterior wall, clear of furniture and not blowing directly onto a bed or desk.

Line length, height difference and the outdoor unit location are checked against the manufacturer's limits. A short, direct run beats a long one in cost and performance.

What does ductless mini split installation involve, and how long does it take?

A single-zone job is usually shorter than a ducted install. Multi-zone work and electrical upgrades extend it. The order is consistent.

1. Run the room load calculation and agree on head locations.
2. Give you a clear, upfront quote that lists lines, electrical work, wall penetrations and the permit.
3. Mount the indoor head and drill one small wall penetration.
4. Set the outdoor unit on a pad or wall brackets, clear of snow drift and downspouts.
5. Connect the line set, drain and control wire, then seal the penetration.
6. Evacuate the lines, open the valves, and test heating and cooling.
7. Show you the remote, filter and condensate path.

What does a mini split cost, and what does Ameren pay?

Inch Calculator, a cost-estimating site, puts installed ductless systems at $2,000 to $14,000, with a single-zone 12,000 Btu system at $3,000 to $4,900 and professional labor at $800 to $2,300 (page updated August 2023; confirm locally). Its figures also add refrigerant lines at $5 to $7 per foot and electrical at $6 to $8 per foot.

Ameren Missouri's chart for 2026 only pays $500 per ton for mini splits at 19+ SEER2, valid January 1 through December 31, 2026. A 1.5-ton system would earn $750 if it qualifies. HVAC rebates run through tier 4 of Pay As You Save (PAYS), and the work must go through a participating contractor who submits the paperwork. Use Ameren's Find a Contractor tool, and confirm everything in writing; a 2027 chart may differ.

Which permit, electrical and license rules apply?

A mini split is mechanical work and generally needs a permit. St. Louis County requires one to install heating or cooling systems, and licenses mechanical contractors through its Department of Transportation and Public Works. Missouri has no statewide HVAC license, and the City of St. Louis requires a City-licensed mechanical contractor for new heating and cooling units.

A new circuit may call for an electrician or an electrical permit, depending on the city. Statewide electrical licensing is voluntary under RSMo 324.900 to 324.945, so local rules decide. Ask each contractor for the license number that applies to your address.

How do you care for a mini split?

Rinse the indoor filter every few weeks during heavy use, keep two feet clear around the outdoor unit, and clear leaves, snow and grass clippings. Schedule a professional check each year to look at the coil, drain and line insulation. Keep the model and serial numbers where you can find them.

Why Kenan Corporation for a ductless project

Ductless work rewards careful design, and these are the proof points behind ours.

• Options explained. A Google reviewer, Candice F., describes Kenan as great at explaining and giving options, which is the point of comparing layouts.
• Load calculation first. We run one before sizing, room by room.
• Open 24 hours. Google lists 4.6★ from 29 reviews as of October 2026.

We install in Jennings, University City, Richmond Heights and Webster Groves. Jennings is about 20 minutes from our base near Spanish Lake in normal traffic; University City and Richmond Heights run about 30 to 35 minutes. See Jennings, University City and Richmond Heights.

Where we install ductless systems

Drive times are normal-traffic estimates from our base and are not arrival promises.

• Jennings, about 20 minutes: 22 percent of occupied homes heat with electricity, so a heat pump head can carry part of that load in a single room.
• Ferguson, about 20 minutes: Old Ferguson West's Victorians have upstairs bedrooms where plaster and framing leave no practical duct path, and Code Compliance takes the permit.
• University City, about 30 minutes: 6,797 of 17,841 units predate 1940, and the city's own permit office sits at City Hall on Delmar Boulevard.
• Richmond Heights, about 35 minutes: median year built is 1947, and the city's mechanical permit rule could not be confirmed online, so call the building office first.
• Clayton, about 35 minutes: 65 percent of units are in multi-unit buildings, so ask the building association where an outdoor unit may sit.
• St. Charles, about 35 minutes: brick buildings near Main Street leave little room for duct runs, and the city licenses HVAC contractors through Community Development.
• Maplewood, about 40 minutes: half the housing is in multi-unit buildings, and the city sends mechanical permits to St. Louis County Public Works.
• Webster Groves, about 40 minutes: with four historic districts, ask the city about wall-mounted hardware on street-facing walls before choosing head and unit locations.
• Kirkwood, about 50 minutes: a municipal electric utility serves about two-thirds of the city, so confirm your utility before counting on Ameren's $500-per-ton rebate.
• Washington, about 1 hour 45 minutes: stone and brick houses in the Tibbe Historic District area may have no duct space, so call first to confirm scheduling this far out.