Mini-Split vs Central AC: Zoning, Duct Losses, and Retrofit Cost
Ductless mini-splits vs central air compared — duct losses, efficiency ratings, zoning, retrofit fit, looks, and which cooling system to install where.
Updated August 22, 2026
A central air conditioner and a ductless mini-split move heat with the same refrigeration cycle; what separates them is the delivery system. Central AC cools air at one indoor coil and pushes it through a duct network to every room. A mini-split skips the ducts entirely: refrigerant lines run through a small wall penetration to one or more indoor heads, each cooling the room it hangs in.
The ducts are where the argument lives. Per DOE Energy Saver, duct losses can account for more than 30% of space-conditioning energy consumption, especially when ducts run through unconditioned spaces like an attic — losses a ductless system never pays. In exchange, the mini-split puts visible equipment on your walls or ceilings and its installed cost can run higher, while a house that already owns a good duct network can swap in a new central system with far less disruption.
Which one belongs in your house is mostly a question of what the house already has: existing ducts favor central, no ducts favor ductless, and single problem rooms favor a one-zone head. Size either system from a real load calculation — the DOE warns that oversized or badly located air handlers short-cycle, wasting energy and losing humidity control.
Side by Side
| Spec | Ductless mini-split | Central (ducted) AC |
|---|---|---|
| System architecture | Outdoor compressor/condenser linked to one or more indoor air-handling heads by a conduit carrying power, refrigerant lines, and a condensate drain — many models support up to four indoor units on one outdoor unit (DOE) | Outdoor condensing unit plus a single indoor coil at a furnace or air handler, distributing cooled air to every room through a supply-and-return duct network |
| Distribution lossesDucts sealed and buried inside the conditioned envelope give up far less than attic ducts — the DOE figure is the warning case, not a constant. | None from ducts — the head conditions the room it serves directly | Duct losses can account for more than 30% of energy consumption for space conditioning, especially when ducts run through unconditioned spaces such as an attic (DOE Energy Saver) |
| Efficiency rating metricsAHRI 210/240 is cited here as the rating basis only; compare specific equipment on its published ratings. | Rated by SEER2/EER2 (and HSPF2 for heat pumps) under AHRI 210/240 test conditions; the units bridge to COP via 3.412 Btu/Wh — EER = COP × 3.412 | Same SEER2/EER2 metrics under the same AHRI 210/240 basis, so ratings compare directly — but a rated SEER2 says nothing about what the duct network then loses |
| Zoning capability | Built in: each indoor head has its own thermostat, so you condition only occupied rooms — the energy-saving feature DOE highlights | One thermostat per system by default; room-by-room control requires a separately designed zoned-damper duct system or multiple systems |
| Retrofit installation profile | Suits houses with no ducts at all — hydronic, radiant, or space-heater homes and room additions (DOE): the hookup generally needs only a 3-inch hole through the wall, and the outdoor unit can sit up to about 50 feet from an indoor head | Straightforward where a duct network already exists and is sound; adding ducts to a house that lacks them is major construction that usually decides the comparison by itself |
| Indoor aesthetics & filtration | Visible wall-hung, ceiling-suspended, flush-mounted, or floor-standing heads about 7 inches deep — sleeker than a window unit, but DOE notes some people dislike the look; each head carries its own small filter to clean | Nothing in the room but registers and grilles; air passes a central filter at the air handler, one point of maintenance for the whole house |
| Heating capability | Most sold today are heat-pump versions that heat and cool; low-temperature heating capacity varies widely by model, so check the manufacturer’s published capacity-vs-outdoor-temperature tables for cold climates | Cooling only — heating comes from the furnace or air handler the coil shares, or from choosing a ducted heat pump instead |
| Cost drivers | Per-zone equipment: every conditioned room needs a head, and DOE notes installed cost can run higher than other systems — offset over time by zoning and the absence of duct losses | One coil and one condenser serve the whole house, so equipment cost per conditioned square foot is low where ducts exist; duct repair, sealing, or construction is the wildcard line item |
Which One for the Job
Adding cooling to a house with a ducted furnace
Central (ducted) AC
The expensive half of a central system — the distribution network — is already installed and already proven by the furnace. An evaporator coil on the plenum and an outdoor condenser buy whole-house cooling with no new equipment in any room; spend part of the savings sealing the ducts so the DOE loss figure stays theoretical.
1950s house with radiators and no ducts anywhere
Ductless mini-split
This is exactly the retrofit DOE names for ductless systems: hydronic-heated homes with no duct path. Retrofitting ductwork means sacrificing closets and chases through finished plaster; a mini-split needs a 3-inch penetration per head, keeps the radiators for winter, and adds heat-pump shoulder-season heating as a bonus.
One hot bonus room over the garage
Ductless mini-split
A single-zone head sized to the one problem room fixes it without touching the rest of the house — the room-addition case DOE calls out where extending ductwork is not feasible. Upsizing the whole central system for one room’s load, or dragging a duct branch across the garage ceiling, costs more and works worse.
Frequently Asked Questions
Do ductless mini-splits really save energy over central air?
Where the ducts are bad, yes, and the mechanism is simple: DOE Energy Saver attributes more than 30% of space-conditioning energy consumption to duct losses in the warning case — leaky runs through unconditioned attics or crawlspaces — and a ductless head pays none of that. A central system with tight, insulated ducts inside the conditioned envelope narrows the gap substantially, so audit the ducts before crediting either side.
How many rooms can one mini-split outdoor unit handle?
Per DOE, many multi-zone models connect as many as four indoor air-handling units to a single outdoor unit, each zone with its own thermostat; how many your house supports depends on the heating and cooling load of each zone, which insulation and air sealing directly affect. Beyond that count you add a second outdoor unit — at which point compare the total against a ducted system’s quote.
What is the difference between SEER2 and the COP a heat pump quotes?
They describe the same physics in different units. COP is dimensionless — watts of heat moved per watt of electricity — while EER states Btu per hour of cooling per watt, so EER = COP × 3.412, the Btu content of a watt-hour. SEER2 then averages that efficiency over a standardized cooling season with the revised (higher static pressure) AHRI 210/240 test conditions. The heat pump COP calculator converts between all three.
Will a mini-split heat pump keep up in a cold climate?
Modern cold-climate models hold useful heating capacity well below freezing, but the honest answer lives in each manufacturer’s capacity-vs-outdoor-temperature table: heat output and efficiency both fall as it gets colder, at rates that differ sharply between models. Size the system against a real heat-loss calculation for your design temperature, and plan supplemental heat where the published curve dips under the load line.
Try the Calculators
Sources
- DOE Energy Saver, "Ductless Minisplit Heat Pumps" — duct-loss share, retrofit applications, zoning, conduit and lineset installation details, indoor-unit form factors, cost and short-cycling cautions (read from Wayback snapshot; the live page was reorganized away)
- AHRI Standard 210/240 — Performance Rating of Unitary Air-Conditioning and Air-Source Heat Pump Equipment (cited as the SEER2/EER2/HSPF2 rating basis; definitions only, no per-model values)
- Heat pump COP calculator source (COP_TO_EER = 3.412 Btu/Wh), the mapped conversion constant