Cooling an Old St. Louis Brick Home Without Ductwork

Cooling an old brick home in St. Louis without ductwork is usually a choice between ductless mini splits, small-duct high-velocity systems and window units. Mini splits are the least invasive, small-duct systems hide the equipment best, and window units are the cheapest for one or two rooms. Which wins depends on rooms, walls and the street.

Why do so many St. Louis brick homes have no ducts?

They were built for radiators. The median home in the City of St. Louis was built in 1938, per ACS data compiled by Neilsberg, and Point2Homes counts 58.4% of City homes, 98,845 of 169,310, as built in 1939 or earlier. Those houses were heated by steam or hot water, with no room for air to travel.

Retrofitting full ductwork means cutting plaster, boxing in soffits or giving up closets. It can be done, and it is often the most expensive way to get air conditioning in.

What are your options for cooling without ducts?

Here are the three realistic paths and their tradeoffs:

ENERGY STAR says mini splits are designed for homes or sections of homes without ductwork, and lists older homes with radiators or baseboard heat as a good fit. Bob Vila's old-house cooling guide describes small flexible ducts that thread through walls, ceilings and floors, and cites $8,000 to $10,000 as a typical price for a high-velocity cooling retrofit. Treat that as a market figure, not a Kenan quote.

Small-duct systems need somewhere to put the air handler, usually an attic with enough height or a dry basement ceiling. Many two-story brick homes have that space, and a bungalow with a shallow attic may not. A technician has to look before anyone can promise it will fit.

Worked example: a two-story brick with three bedrooms upstairs

This is an illustration, not a job we did. The bedrooms are under the roof, one has a west window, and the attic is too shallow for a small-duct air handler. The family wants to keep the radiators and the plaster.

Ask for the layout options priced side by side. The right pick depends on how many outdoor units the side yard and the street view can take.

Drains, line sets and wiring: the old-house details

The unglamorous parts decide whether the install looks good:

• Condensate. Every indoor head drips water while it cools. It needs a gravity path to the outdoors or a basement drain, or a small pump when the slope is wrong.
• Line-set route. The refrigerant lines can run behind an exterior cover, through the attic, or up a closet chase. Cutting plaster is the last resort.
• Electrical. Most mini splits call for a dedicated circuit, and the installation manual sets the breaker size. Two-prong outlets and an old fuse box are reasons to bring in an electrician first.

What a good site visit covers

A proposal written from a phone description is a guess. A site visit should walk through six things:

1. Each room you want cooled, with its window count and orientation
2. Attic access and headroom, if small-duct is on the table
3. The electrical panel and any spare breaker space
4. Two or three candidate condenser spots
5. The path through the wall for the line set
6. Where each head's condensate drain will go

Cut the load before you size the system

Equipment is sized to the heat it has to remove, so shrink that heat first. Attic insulation and air sealing, shades or awnings on west windows, and tight storm windows all lower the load. The trade-off is that these steps help the equipment, but they will not replace it on a 95-degree afternoon. Do them in the same year, not instead.

How do mini splits work with thick masonry walls?

Brick holds heat. A south wall that soaked up sun at 4 pm is still radiating at 9 pm, so a bedroom may need more capacity than its floor area suggests. A load calculation that accounts for wall construction, window type and attic insulation gives a better size than a rule of thumb.

Installation is gentler than you might fear. A mini split needs one small core hole through the wall for the line set rather than a large duct opening, so mortar and brick are disturbed in a single spot. Our ductless mini split page explains the process, and AC installation covers sizing.

Two things to check early are the electrical panel and the condenser location. An older panel may have no spare breaker space, and a street-facing wall may not be the right spot for the outdoor unit.

Do historic district rules affect the choice?

They can. The City of St. Louis Cultural Resources Office reviews exterior work in local historic districts, City landmarks and similar properties. Each local district has its own standards, so what is allowed in one may need review in another. Call the office at (314) 657-3865 before you commit to a condenser on a street-facing wall.

Houses outside the city, such as those in Jennings or University City, follow their own municipal rules. Check with the local building office whether any exterior equipment or permit applies.

What about rebates?

Ameren Missouri's 2026 chart lists $500 per ton for mini splits at 19 SEER2 or higher, valid through December 31, 2026 and only through its PAYS program with a participating contractor. A 2027 chart may differ, so confirm it before you sign. Our rebates guide covers the checklist.

From the field: choosing among imperfect options

No cooling option is perfect in an old house. A Google reviewer, Candice F., wrote that Kenan is great at explaining things and giving you options. That is the right test for any contractor you hire here. A good proposal shows two or three layouts, with the number of heads, the rooms covered and the visible tradeoffs, and then lets you choose.

Another reviewer, Ms. O., described an old, rusty air conditioner that leaked water and could no longer hold the house at temperature. A new system fixed it. If your current setup is a tired window unit, the same logic applies to your bedrooms.

Talk it through before you commit

Talk to a specialist at (321) 478-0693 and describe the house: floors, radiators or boiler, attic access and the rooms you want cooled. We are open 24 hours, we run a load calculation before sizing, and we give a clear, upfront quote before work starts. Jennings is about 20 minutes from our base near Spanish Lake in normal traffic.