Ducted vs ductless heat pump is a choice about delivery, not technology. Both are air-source heat pumps that heat and cool. A ducted system sends air through the house’s ductwork from one indoor unit; a ductless mini split puts an indoor unit in each room or zone. Usable ducts usually favor ducted; no ducts often favor ductless.
Key takeaways
- A ductless mini split is a heat pump; it delivers heat through room units instead of ducts.
- Houses with usable ducts are the natural fit for a ducted heat pump; houses with baseboard or radiators often suit ductless better.
- Neither is automatically more efficient: duct condition and location decide most of the real-world gap.
- The Seattle Heat Pump Company plans ducted systems only and does not install ductless equipment.
The Seattle Heat Pump Company plans and manages ducted heat pump installations in Seattle and King County, with the work carried out by licensed and insured contractors. We do not install ductless systems. That makes this guide a little unusual: it explains plainly when ductless is the better fit, even though that is work we do not do, because a heat pump in the wrong format serves no one.
Same machine, different delivery
A heat pump moves heat between indoor and outdoor air using refrigerant, a compressor and two coils. In both formats, an outdoor unit holds the compressor and the outdoor coil, and insulated refrigerant lines connect it to the indoor side.
The difference is what happens indoors. A ducted heat pump has one indoor coil, either on top of a gas furnace or inside an electric air handler, and a blower pushes air across it and through supply ducts to every room, with return ducts bringing air back. A ductless heat pump, usually called a mini split, runs refrigerant lines to one or more indoor units mounted on walls or ceilings. Each indoor unit has its own coil and fan and conditions the room it sits in. A multi-zone system connects several indoor units to one outdoor unit.
So when people compare a “heat pump vs mini split,” they are usually comparing a ducted heat pump with a ductless one. The how a ducted heat pump works guide covers the ducted side in more depth.
Side by side
| Ducted heat pump | Ductless mini split | |
|---|---|---|
| Indoor equipment | One coil and blower, on a furnace or in an air handler, usually out of sight | One indoor unit per room or zone, visible on a wall or ceiling |
| Air delivery | Through supply and return ducts to every room | Directly into the room from each unit |
| Best match | Houses with existing usable ducts | Houses without ducts, additions, single rooms |
| Zoning | Whole house on one thermostat, unless dampers are added | Each indoor unit has its own control |
| Filtration | One central filter, can take higher-grade media | A washable filter in each indoor unit |
| Works with a gas furnace | Yes, as dual fuel | No; it runs independently of a furnace |
| Duct losses | Depend on duct condition and location | None |
| Seattle refrigeration permit | Required | Required |
| Seattle side-yard noise review | Required | Not required unless there is a complaint |
| City Light discount | $300 or $600 by efficiency tier | $400 tier for mini and multi-split systems |
What Seattle permit data shows
Both formats are common in Seattle. Of the 19,466 single-family and duplex trade permits mentioning a heat pump over the latest three years of records, about 26% describe ducted equipment, such as ducts, an air handler, a furnace or central air, and about 36% describe ductless or mini-split equipment. The rest do not say. Regionally, NEEA’s 2022 survey found that 49% of Washington single-family homes heat primarily with a furnace and 19% with a central heat pump, both ducted, while 13% rely on baseboard or wall heaters, which have no ducts.
That split reflects the housing. Where a house was built around a furnace and ducts, a ducted heat pump replaces the furnace on the same distribution, which is the furnace to heat pump conversion path. Where it was built with baseboard heat or a boiler and radiators, there is nothing for a ducted system to connect to.
When ducted fits better
A ducted heat pump is usually the stronger choice when:
- The house already has ducts that test well, or can with modest fixes such as an added return and sealed joints. The distribution is already paid for and hidden in the walls and floors.
- You want the whole house conditioned evenly, including bedrooms, bathrooms and hallways that would not each get their own ductless unit.
- You want to keep the gas furnace as backup. A heat pump coil on the furnace makes a dual fuel system, which ductless cannot do.
- You prefer no equipment in the rooms, just registers and a thermostat.
- Central filtration matters to you, since one air handler can take a thicker, higher-grade filter than small room units.
Ducts are also the main risk in a ducted system. A heat pump moves more air than a furnace to deliver the same heat, so a single small return or undersized branch can leave rooms cold. A static pressure test before equipment is chosen tells you whether your ducts are ready. See using a heat pump with existing ductwork.
When ductless fits better
This is the section we are writing against our own interest. Ductless is often the better answer in these houses, and if yours is one of them, a mini-split specialist is the right call rather than us.
Houses with no ducts
Homes heated by electric baseboard, wall heaters or a boiler with radiators have no duct system. Putting in a ducted heat pump means designing and building ducts from scratch: finding routes through walls, floors, an attic or a crawlspace, and patching finishes afterward. In some houses that is practical, especially with an open crawlspace and attic. In many it is not, and ductless units deliver heat and cooling to the main rooms with only small holes through exterior walls for the refrigerant lines. For PSE electric customers replacing resistance heat, PSE offers a conversion rebate for air-source heat pumps; confirm with PSE which equipment qualifies, and see the PSE rebate guide.
Additions, converted attics and detached spaces
A finished attic, a garage converted to living space, an addition or a detached backyard unit often sits beyond the reach of the existing ducts, or would overload them. A single ductless unit conditions that space on its own control without touching the main system.
Ducts that are beyond saving
Some older Seattle houses still have the large round ducts of an early gravity furnace, or duct systems pieced together over decades. Sometimes those can be reworked or replaced at reasonable cost. Sometimes replacing them would mean opening plaster walls throughout the house, and ductless becomes the more sensible route. There is no local data on how common each case is, so this is something to have measured, not assumed. The older homes page covers what an assessment looks for.
Efficiency: does ductless always win?
No. Ductless systems have one built-in advantage: no ducts, so no air leaks into crawlspaces or attics and no heat lost through duct walls. Published SEER2 and HSPF2 ratings for ductless equipment also often run higher, partly because the test does not push air through a duct system.
But the real-world gap depends on the ducts you would otherwise use. Tight, well-sized ducts inside the heated part of the house lose very little. Leaky ducts running through a cold, vented crawlspace lose a lot. Sealing and insulating ducts, or adding a return, can close much of the gap. And a ductless system with too many oversized indoor units can cycle on and off and run less efficiently than its rating suggests. Comparing ratings alone misses all of that. The SEER2 and HSPF2 guide explains what the ratings measure, and the sizing guide covers why the load calculation matters in both formats.
Comfort, looks and upkeep
Comfort. A ducted system conditions every room with a register, which keeps temperatures even through the house if the ducts are balanced. A ductless system conditions the rooms with indoor units well, and rooms without one depend on air drifting through open doors. Bedrooms with doors closed often need their own unit.
Looks. Ducted equipment hides in a basement, closet, crawlspace or attic. Ductless indoor units are visible, and line sets often run on the outside of the house in covers.
Upkeep. A ducted system has one filter to change and one condensate drain to keep clear. A ductless system has a filter in every indoor unit, and each unit’s coil and fan need periodic cleaning. The maintenance guide covers the ducted side.
Find out whether your ducts can carry a heat pumpAn assessment measures the ducts, the load and the panel, and tells you plainly if ducted is the wrong fit.
Get an EstimateCost structure
A ducted heat pump on usable ducts typically runs about $6,700 to $20,000 in the Seattle area. The ducts are the swing factor: sealing and an added return keep a project near the published range, while whole-house duct replacement runs about $1,400 to $5,600 in HomeGuide’s national figures and up to about $17,100 for complex installs in Fixr’s figures. The installation cost guide covers the drivers.
We do not publish ductless prices, because we do not install ductless systems. What drives ductless cost is the number of indoor units, the length of each line set route, whether a condensate pump is needed for each unit, and the electrical work. A multi-room ductless system adds an indoor unit, and its cost, for each zone.
Permits, noise and incentives in Seattle
Both formats are split systems, so in Seattle both need a refrigeration permit, which only a licensed refrigeration contractor can obtain, plus an electrical permit. A ducted system also needs a mechanical permit when the indoor equipment is installed or altered.
Noise is handled differently. Seattle’s noise code limits residential sound at the property line to 55 dBA by day and 45 dBA at night for any equipment. For ducted heat pumps, the city adds a noise review whenever the outdoor unit is in a side yard, and a predicted level of 47 dBA or less on the heating rating passes. Ductless systems need no noise review unless there is a complaint, though they still have to meet the limits. The noise ordinance guide explains the review.
City Light’s contractor discount pays $300 or $600 on ducted heat pumps by efficiency tier and $400 on qualifying mini-split and multi-split systems, one system per home. The rebate guide covers the full list.
Mixed systems
Many houses end up with both: a ducted heat pump on the existing ducts for the main floors, and a ductless unit for a space the ducts never reached. That approach keeps the hidden, whole-house distribution where it works and avoids stretching undersized ducts to reach an addition. If that is where your house lands, we plan the ducted system, and a mini-split specialist handles the ductless unit.
How to decide
Start with three questions:
- Does the house have ducts, and do they pass a static pressure test? If yes, ducted is usually the natural fit.
- Are there rooms the ducts do not reach, or reach poorly? Those are candidates for duct fixes or a separate ductless unit.
- Do you want to keep a gas furnace as backup? Only a ducted system can pair with it.
An assessment answers the first two with measurements. If the answer is that your house needs ductless, we will say so. If it is ducted, the cost estimator gives a range, and a call or a few details about the house gets the planning started.