Ducted vs Split-System Heat Pumps: Which One Actually Fits Your Home

Around eighteen months ago I sat in a client's roof cavity in Melbourne's outer east with a tape measure, working out whether there was enough room for return-air ducting between the trusses. There wasn't, not without dropping the ceiling in two rooms. That conversation, ducted or split, comes up on almost every consult I do, and the honest answer is that it depends on things a glossy brochure won't tell you.

A ducted heat pump puts one outdoor unit and one indoor fan-coil unit in the roof space, then distributes heated or cooled air through a network of ducts to registers in each room. A split system puts a separate indoor head in each room you want to condition, each wired back to its own (or a shared multi-head) outdoor compressor. Both use the same refrigeration cycle we've covered elsewhere on this site. The difference is entirely about distribution, not the underlying technology.

Where ducted wins

Ducted is the better fit when you want the whole home conditioned to a similar temperature, you value not seeing indoor units on the walls, and, this is the part people underestimate, you actually have the roof space and access for it. A single-storey home with a pitched roof and decent truss spacing is usually straightforward. A home with a flat or skillion roof, or one already crowded with solar conduit and insulation batts, can turn a "simple ducted retrofit" into a much bigger job than the quote implied. I've had installs blow out by a full day once we found the roof cavity had barely enough clearance to crawl through, let alone run 250mm flexible duct.

Ducted systems also do zoning well when specified properly. Motorised dampers let you close off unused rooms so the system isn't wasting capacity heating a spare bedroom nobody's in. The catch is that zoning has to be designed in from the start. I've seen too many project-home installs where "zoning" means one thermostat and a single zone covering the whole house, because it was cheaper to install that way and nobody flagged the tradeoff at quote time. Ask specifically how many zones are being installed and whether each has its own damper and sensor, not just a single return-air sensor reading the hallway.

Where split systems win

Splits are the right call for a room-by-room retrofit: an extension, a granny flat, a single room that's always too hot or too cold relative to the rest of the house. They're also usually cheaper to install per room if you genuinely only need one or two rooms conditioned, since you're not paying for ductwork and a full-house fan coil you'll only half use. A single split can be running within a day. A ducted retrofit into an existing roof is realistically a two-to-three-day job once you include ceiling access, electrical upgrades and commissioning.

The tradeoff is aesthetic and, over enough rooms, financial. Five rooms means five indoor heads, five sets of remote controls (unless you spring for a proper multi-head controller), and five things on the wall. Once you're past three or four rooms a well-designed ducted system with real zoning often ends up cheaper and tidier than an equivalent spread of splits. The crossover point in my experience sits somewhere around four to six rooms, though it moves a lot depending on your specific floor plan and how far apart the rooms needing conditioning actually are.

A worked example from a recent job

A client in Ringwood had a four-bedroom single-storey home and was leaning toward five separate splits, one per living zone. Once we mapped the actual roof truss layout, there was clean access for ducting through the whole footprint, and a two-zone ducted system (living areas on one zone, bedrooms on another) came in cheaper than five splits over a ten-year horizon once you accounted for five separate services and five sets of ageing compressors failing on different schedules. That won't be true for every home. It's exactly the kind of comparison a good installer should run for you rather than defaulting to whichever system they happen to prefer selling.

The sizing conversation nobody wants to have

Whichever direction you go, the installer should be doing an actual heat-loss and heat-gain calculation on your home, not eyeballing floor area and applying a rule of thumb. I still see oversized systems quoted because a bigger unit is an easier sale than a correctly sized one paired with an honest conversation about your insulation. An oversized heat pump short-cycles, which is hard on the compressor and worse for humidity control in cooling mode than a correctly sized unit running longer, gentler cycles. If your quote doesn't mention a heat-loss calculation, ask for one before you sign.

Running cost differences in practice

People assume ducted must cost more to run because it's conditioning more air. That's often true if you're heating the whole house when you only need two rooms warm, but a well-zoned ducted system closing off six of eight rooms overnight can be genuinely competitive with splits, room for room. What actually drives the bill is whether the system is matched to how you live in the house, not the distribution method in the abstract. I'd rather see a smaller, well-zoned ducted system than an oversized one "for flexibility," because that flexibility rarely gets used and the running cost doesn't reflect it.

What I'd actually do

For a whole-home renovation or new build where the roof space is designed in from the start, I lean ducted with proper zoning. It ages better and keeps the walls clear. For a retrofit into an existing home with limited roof access, or where you genuinely only need one or two rooms conditioned, splits usually make more financial and practical sense, and you're not gambling on what's actually up in that ceiling cavity until the installer has been up there with a torch.

Whatever you land on, get the sizing calculation in writing and ask what happens to ducted access if you add solar or extra insulation later. Both of those change the roof-space equation, and it's cheaper to plan for it now than to re-route ductwork around a battery inverter in two years' time. See our explainer on how heat pumps actually work for the refrigeration-cycle basics behind both system types, and our running-cost comparison against gas if you're still deciding whether to electrify heating at all. If you're at the quoting stage, our guide on choosing a trade covers what a proper heat-loss-based quote should look like.

Manufacturer capacity and zoning specifications are published by bodies like the Air-Conditioning, Heating and Refrigeration Institute (AHRI) in the US, and installation and efficiency standards in Australia sit under the Australian Government's Energy Rating scheme. Both are worth a look if you want to check a specific model's certified output rather than trusting a brochure number.

What I ask clients before recommending either

I run through the same short list every time. How many rooms need conditioning at once, and how often. Whether the household wants uniform whole-house temperature or is happy with some rooms warmer than others. What the roof cavity actually looks like, not what the original floor plan suggests it should look like. And whether there's a renovation or extension likely in the next five years, because a ducted system designed for today's floor plan can be expensive to extend later, while an extra split can just be added to an existing multi-head outdoor unit if there's spare capacity. None of these questions has a universally right answer. They're the actual inputs that should drive the recommendation, rather than an installer defaulting to whichever system is easier for their crew to install that week.

One thing I'd flag honestly: the split-system market has a much wider spread of quality between the cheapest and most reputable brands than the ducted market does, partly because ducted installs are a bigger, more considered purchase that buyers tend to research harder. If you're going the split route, don't assume all splits are roughly equivalent just because the technology is the same. Compressor quality, refrigerant management and long-term parts availability vary a lot between manufacturers, and it's worth asking your installer directly which brands they've had good long-term service experience with, not just which one they happen to stock.

— Priya Nathan, Heat pumps & HVAC