Mini-splits and multi-zone systems
How ductless systems work, how many indoor heads a home actually needs, where they should go, and the trap most people fall into when they buy a multi-zone.
One outdoor unit, one or more indoor heads
A ductless mini-split splits the system in two. The outdoor unit holds the compressor. Inside, a wall-mounted head blows conditioned air directly into the room. The only thing connecting them is a small bundle of refrigerant lines, a drain and a power cable through a three-inch hole in the wall.
No ductwork. That is the whole appeal. In a 1950s North Shore house with baseboard heaters and no duct runs anywhere, retrofitting ducts is expensive and ugly. A ductless system sidesteps the problem entirely.
A single-zone system is one outdoor unit serving one indoor head. A multi-zone system is one outdoor unit serving several, each with its own thermostat, each able to run or not run independently.
How many heads do I need?
The honest answer is one per area you want independently controlled — not one per room, and not one for the whole floor.
A head conditions the space it can actually blow air into. It will not push heat around a corner, down a hallway, or through a closed door. An open-plan living, kitchen and dining area is usually one zone. Three bedrooms off a hallway are usually three zones, or none, depending on how you live.
Bedrooms are the decision most people get wrong in both directions. Some put a head in every bedroom and spend thousands on capacity that runs a few hours a week. Others put none in, then find the bedrooms are the only uncomfortable rooms in the house.
What we ask on site: which rooms are uncomfortable now, which doors stay shut, and who sleeps where.
The multi-zone trap
Here is the thing almost nobody is told at quoting time.
On most multi-zone systems the indoor heads can be sized to add up to more capacity than the outdoor unit can deliver. That is normal and intended — not every room calls for heat at once.
The problem is at the other end. A multi-zone outdoor unit has a minimum output it cannot go below. If only one small bedroom head is calling on a mild October evening, the outdoor unit may be forced to run harder than the house needs, then cycle off, then start again.
That is why a three-head multi-zone can feel worse in shoulder season than a single well-chosen unit. It is also why we would rather talk you out of a head you do not need than sell you one.
When ducted wins
- You already have ductwork in usable condition
- You want even temperatures without visible wall units
- You want proper filtration for the whole house
- You have many small rooms, where a head each is uneconomic
- Resale matters to you and wall heads are a sticking point
A ducted heat pump and a ductless multi-zone are not competing products so much as answers to different buildings. How heat pumps work.
Where the equipment goes matters
Placement decisions are permanent in practice. They are worth getting right before anyone drills.
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Indoor heads
High on an interior wall, blowing across the room, not straight down at a sofa or a bed. Avoid blowing directly at where people sit.
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Outdoor unit noise
It makes noise, most of all during defrost. Under a bedroom window or hard against a neighbour's wall is a decision you will live with.
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Condensate drainage
Every head makes water in cooling mode. It has to go somewhere by gravity, or a small pump has to move it. Badly drained heads stain walls.
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Line routing
Shorter and straighter runs perform better. Long routes around the outside of a house are sometimes unavoidable, but they cost capacity.
Questions we get on the phone
Can one head heat my whole house?
Only if your house is effectively one open space. Air does not travel through closed doors. A single head in a living room will leave the bedrooms cold, whatever its capacity.
Do mini-splits cool as well as heat?
Yes — it is the same machine running in reverse. On the coast that matters more every summer, and it is one of the strongest reasons to choose a heat pump over any heating-only replacement.
Are they ugly?
Opinions differ and it is a fair concern. Modern heads are slimmer than the ones people picture. Where there is a ceiling cavity or a soffit, concealed and cassette units are available at more cost.
How much maintenance do they need?
Filters need rinsing regularly — monthly in a busy house. Beyond that, an annual service to clean the coils and check the charge. Neglected indoor heads grow mould in the blower wheel, which is unpleasant and avoidable.
Do they qualify for rebates?
Often, though whole-home and partial systems are treated differently, and the equipment has to meet the programme's efficiency requirements. See what decides your amount.
Not sure how many zones you need?
Tell us which rooms are uncomfortable and which doors stay shut. That conversation decides the system more than the square footage does.