Ductless Mini-Splits

Four things move it, and none of them is the brand. The number of zones and the capacity each one needs. The style of indoor unit — a cassette recessed into a finished ceiling is more work than a head screwed to an exterior wall. The line set run, which is cheap through a basement and expensive up three storeys of a party wall. And the electrical: whether there is a spare circuit and panel capacity, or whether a sub-panel is part of the job. We price after the site visit, and state and utility incentives plus financing both apply.

Fewer than most people expect, and the common mistake is buying one per room. An open-plan floor with good air movement is often one well-placed unit. Rooms behind doors that stay closed need their own. A single outdoor condenser can carry several indoor units, but there is a floor to how far each one modulates down, so a tiny bedroom head on a large multi-zone system will short-cycle. Sometimes two smaller condensers beat one big one.

Yes, provided there is depth above the ceiling to take the body of the unit — an attic, a joist bay that will accept it, or a soffit that can be built. Full-size cassettes want real clearance; one-way and compact models slot into ordinary residential joist spacing. A cassette also needs a condensate lift pump, since there is no gravity fall from a ceiling. We check the cavity on the site visit before anything is promised.

Usually the condensate path, not the refrigerant. The drain line is blocked with the biofilm that grows in a damp plastic tube, the pump has failed or its float is stuck, or the line was run with a rise in it and water is backing up. Less often it is ice melting off a coil that froze because the filter is loaded or the charge is low. Switch the unit off if it is dripping onto plaster or a floor and get it looked at — the drip is cheap, the ceiling underneath is not.

More than any other system in the house, and this is the failing we see most. The mesh filters need rinsing every few weeks in season — that part is yours. The blower wheel and the coil behind it need a proper deep clean roughly every other year, because a ductless head has no filter rack in front of it and the wheel builds a fur of dust that goes musty. A unit blowing a smell a minute after starting is overdue.

Indoors, a modern inverter head at low speed is quieter than the conversation happening under it — quieter than a ducted system, because there is no return grille roaring in a hallway. Outdoors is the part worth planning: the condenser is small but it runs long and slow, so we site it away from bedroom windows and off the neighbour’s property line, on brackets or a stand rather than tight against a resonant wall.

The cold-climate models do, and they are what we specify for anything expected to carry a room through the season rather than just take the edge off. The equipment is a heat pump with the indoor half hung on a wall, so the same sizing discipline applies: the capacity that matters is the one at the winter design temperature, not the headline figure. A floor console suits a heating-led room better than a high-wall head.

A compact air handler feeding small flexible tubing that threads through existing wall and floor cavities, ending in outlets a few inches across that disappear into a ceiling or baseboard. It suits period houses where nothing may be visible and the plaster must stay intact. The trade-off: one zone unless you add controls, a mechanical space is needed for the air handler, and it is a more invasive install. Where appearance decides, it wins; where per-room control decides, ductless does.