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Ducted system vs ductless mini-split: which to install
Existing ductwork and whole-building ventilation favor ducted; no ducts and room-by-room zoning favor ductless.
Short answer
Pick a ducted system when usable ductwork already exists or the building needs whole-house airflow with ventilation and filtration in one path; pick a ductless mini-split when there are no ducts, running them is expensive or destructive, or you need independent room-by-room setpoints. The single biggest deciding factor is the ductwork: a mini-split earns its place on retrofits, additions, and rooms a central duct system never reached, because you skip the cost and demolition of running duct. If ducts are already there and one main zone suits the space, ducted usually wins on first cost and built-in ventilation.
Ducted system vs Ductless mini-split: side by side
| Factor | Ducted system | Ductless mini-split |
|---|---|---|
| Distribution | Conditions air centrally and ducts it to the rooms | Runs refrigerant lineset to each head, which blows into the room; no duct |
| Zoning | One main zone served well; more zones need dampers or a second system | Each head is its own zone with its own remote and setpoint |
| Field refrigerant connections | Lineset brazed to coil and condenser; flow nitrogen while brazing | Flared and torqued mechanical joints, no torch on a standard install |
| Ventilation / fresh air | All-air path carries ventilation with economizer and outside-air damper | Recirculates room air only; add a separate OA path, ERV, or DOAS |
| Efficiency | Loses delivered capacity to duct leakage and reach over distance | Inverter modulates at part load with no duct losses; rated SEER2/HSPF2 |
| Install disruption | Running duct adds cost and demolition where it does not exist | Skip the duct; lineset, drain, and comms leave through one wall penetration |
| Main callback source | Duct leakage and reach; brazed-joint and charge issues | Flare weep and condensate drip from a head not sloped to drain |
| Charge / commissioning | Field braze, evacuate, set charge by subcool or superheat | Factory pre-charge (often ~25 ft/port) plus per-foot adder; evac ~500 microns |
| Best use | Homes and buildings with existing ductwork and one main open zone | No-duct retrofits, additions, and single rooms needing their own zone |
Which should you pick?
Choose Ducted system when
- Usable ductwork already exists or the design includes it
- One main open zone with whole-house even airflow
- You want ventilation and filtration handled in one central air path
- Central filtration and humidity control for the whole envelope
Choose Ductless mini-split when
- Retrofit, addition, or a room the central duct system never reached
- Room-by-room zoning with an independent setpoint per head
- You want to avoid the cost and demolition of running duct
- Cold-climate primary heat, with rated output on some models to about -13 to -22 F
Bottom line
It depends on the ductwork and the ventilation plan. Where ducts already exist and the space is one main zone, a ducted system is usually cheaper to install and ventilates in one path. Where there is no duct, running it is expensive or destructive, or the building needs fine room-by-room control, a ductless mini-split wins by going refrigerant straight to the zone and zoning without dampers. The catch on ductless is that it brings in no fresh air on its own, so the ventilation path has to be planned separately, and multi-zone head cost adds up. Run the load, map how the building zones, and confirm the ventilation path before the bid locks it in.
FAQ
Is a ductless mini-split cheaper than a ducted system?
It depends on the ductwork. In a space with no duct, a mini-split is often cheaper because you skip the cost and demolition of running duct. Where ducts already exist, a ducted system usually wins on first cost, and a multi-head multi-zone mini-split adds up fast because each head is its own unit to buy and hang.
Can a ductless mini-split replace a whole ducted system?
Yes, a multi-zone mini-split can condition several rooms off one outdoor unit, each head its own zone. Two things to plan: it recirculates room air and brings in no fresh air on its own, so ventilation must be added separately, and the indoor heads are visible in each room rather than hidden behind grilles.
Which is more efficient, ducted or ductless?
It is design dependent, but a ductless mini-split avoids the duct leakage and reach losses a ducted system carries, and its inverter compressor modulates at part load instead of cycling full on and off. That part-load running is why mini-splits post the SEER2 and HSPF2 numbers they do. A tight, sealed duct system narrows the gap; a leaky one loses delivered capacity.