The Short Version

A mini split — also called a ductless mini split or ductless heat pump — is a heating and cooling system that moves heat between the outdoors and a room without using any ductwork. One outdoor unit connects to one or more indoor air handlers mounted on the wall, ceiling, or floor. Each indoor unit conditions only the space it serves.

Mini splits are common in room additions, garages, older homes without ducts, and any space where running new ductwork would be impractical or expensive.

How a Mini Split Works

A mini split operates on the same refrigerant-cycle principle as a central air conditioner or heat pump — it just skips the ductwork. Here's the basic sequence:

• Cooling mode: The indoor unit absorbs heat from the room air into refrigerant. That refrigerant travels through a small refrigerant line set (typically 1–2 inches in diameter) to the outdoor unit, which releases the heat outside. Cool air is blown back into the room.
• Heating mode: The cycle reverses. The outdoor unit extracts heat from outside air — even at temperatures well below freezing — and delivers it to the indoor unit, which releases it into the room.

The refrigerant line set, a power cable, and a condensate drain line run through a small hole (typically 3 inches) in the wall. That's the only penetration required.

Single-Zone vs. Multi-Zone

A single-zone system pairs one outdoor unit with one indoor unit. It's the simplest and least expensive configuration — ideal for one room or one addition.

A multi-zone system connects one outdoor unit to two, three, four, or more indoor units, each in a different room. Each zone has its own thermostat and can be set independently. Multi-zone systems cost more upfront but can replace a whole-home HVAC system in homes without existing ductwork.

Indoor Unit Styles

Mini splits come in several indoor unit configurations to fit different spaces:

• High-wall mount: The most common style — mounted near the ceiling on an exterior or interior wall. Unobtrusive and easy to install.
• Ceiling cassette: Recessed into the ceiling and distributes air in four directions. Popular in open-plan spaces and commercial settings.
• Floor console: Sits near the floor, similar to a baseboard heater. Good for rooms with limited wall space or large windows.
• Concealed ducted: Hidden in the ceiling with short duct runs to one or two registers. Looks like a traditional system from inside the room.

Efficiency: Why Mini Splits Are So Efficient

Central forced-air systems lose 20–30% of their conditioned air through duct leaks and heat transfer through duct walls. Mini splits have no ducts, so there's no duct loss. That's the primary reason mini splits routinely achieve SEER2 ratings of 18–26+, compared to 14–18 SEER2 for most central systems.

Variable-speed (inverter-driven) compressors also help. Instead of cycling on and off at full capacity, the compressor modulates its speed to match the exact load — running slower and more efficiently when the demand is low.

Mini Splits in Chicago's Climate

Chicago winters are cold — temperatures regularly drop into the single digits and below zero. Standard mini splits lose capacity and efficiency as outdoor temperatures fall. Cold-climate mini splits (sometimes called hyper-heat or cold-climate heat pumps) are designed to maintain full or near-full heating capacity down to -13°F to -22°F, making them viable as a primary heat source in Chicago.

If you're considering a mini split as your only heat source in Chicago, confirm the model's rated heating capacity at 5°F and 0°F — not just at 47°F, which is the standard test condition. D's Air & Heating can help you select the right model for Chicago's climate.

What Mini Splits Are Good For

• Room additions, sunrooms, and converted spaces that aren't connected to the main duct system
• Garages, workshops, and finished basements
• Older Chicago homes (bungalows, two-flats, greystones) with radiator heat and no cooling
• Supplemental cooling in rooms that are always too hot or too cold
• Whole-home heating and cooling in homes without existing ductwork

What Mini Splits Are Not Good For

• Homes with existing ductwork in good condition — a central system is usually more cost-effective
• Spaces where wall or ceiling mounting is not practical
• Homeowners who strongly dislike the look of wall-mounted units (though floor consoles and cassettes are alternatives)

Installation Overview

A typical single-zone mini split installation takes 4–8 hours. The technician mounts the indoor unit, drills a 3-inch hole through the wall, runs the line set and wiring to the outdoor unit, vacuums the refrigerant lines, and charges the system. No ductwork, no major construction.

Multi-zone systems take longer — typically one to two days depending on the number of zones and the complexity of the line set routing.

D's Air & Heating installs mini splits throughout Chicago and the surrounding suburbs. Every installation includes proper line set sizing, refrigerant charging to manufacturer specifications, and a full system startup and test.