Mini split installation, zone by zone

What is mini split installation?

A mini split is a ductless heat pump: an outdoor compressor connected by a slim refrigerant line set to one or more wall, ceiling or floor units inside. Each indoor head is its own zone with its own thermostat. A single-zone install is typically a half day to a day; multi-zone systems take longer because every head needs its own line run back to the outdoor unit.

Signs you need mini split installation

• You have a room the ducted system has never reached - a bonus room over the garage, a finished attic, a sunroom
• You are converting a garage, basement or outbuilding and extending the existing ductwork is impractical
• The house has no ductwork at all - hydronic baseboard, radiators, or electric resistance heat
• One or two rooms are consistently much hotter or colder than the rest and balancing the ducts has not fixed it
• You are running window units or portable ACs and want something quieter, more efficient and permanent
• Someone in the house wants a different temperature to everyone else, and the thermostat war is real
• You want to heat and cool a home office or workshop without conditioning the whole building to do it

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How mini split installation actually works

1. 1

   Room-by-room load calculation

   Each zone gets sized on its own, not on floor area. A south-facing sunroom with a lot of glass and a shaded interior bedroom of the same size need very different capacities.

   Watch forSizing from a chart of square footage to BTU. Oversized mini split heads are worse than oversized ducted systems: an inverter compressor already modulates down, and a head that is too large for its room will sit at minimum output, cycle, and never dehumidify properly.

2. 2

   Single zone or multi zone

   A single-zone system pairs one outdoor unit with one head. A multi-zone runs several heads from one outdoor unit. Multi-zone is tidier outside and shares one condenser; single zones are cheaper per unit, fail independently, and often modulate better.

   Watch forA multi-zone sold purely because it is one box outside. If one head is running and the others are off, some multi-zone systems run inefficiently at very low load. For two zones far apart in a house, two single-zone systems are frequently the better engineering answer.

3. 3

   Indoor head placement

   Wall units usually go high on an interior or exterior wall with clear space around them and a straight path for the line set to leave the building. Ceiling cassettes and floor-mounted units exist for rooms where a high wall unit is impractical or unwelcome.

   Watch forA head placed where the line set is easiest to run rather than where the air needs to go. Blowing across a doorway, straight at a bed, or into a wardrobe alcove is a comfort complaint you will live with for fifteen years to save an afternoon of routing.

4. 4

   Outdoor unit siting

   The condenser needs clearance for airflow, a level mounting pad or wall bracket, and somewhere that its noise and its winter defrost water are not a problem. In cold climates it is raised above expected snow depth on a stand.

   Watch forA condenser under a bedroom window or hard against a neighbour's boundary. It runs at night in summer. Also watch for units set at ground level in snow country - a heat pump that drifts over stops working when you need it most.

5. 5

   Line set routing and the wall penetration

   A three-inch hole through the wall carries the refrigerant lines, condensate drain and control wiring. Outside they run in a line-hide cover to the condenser. Shorter and straighter runs perform better and cost less.

   Watch forBare, untidy line sets taped to the exterior. It is not just cosmetic - unprotected insulation degrades in UV and the performance goes with it. Also make sure the condensate line falls continuously; a head that has to drain uphill needs a condensate pump, and that should be quoted, not improvised.

6. 6

   Electrical supply

   Most systems need a dedicated circuit and a disconnect at the outdoor unit. Multi-zone systems and larger single zones frequently need 240V, which in an older house can mean panel work.

   Watch forThe panel checked on install day rather than at the site visit. This is the most common cause of a mini split job stopping halfway through with the wall already drilled.

7. 7

   Evacuation, charge and commissioning

   Lines are pressure-tested with nitrogen, evacuated to a deep vacuum, then the factory charge in the condenser is released. Longer runs need additional refrigerant added by weight to the manufacturer's specification.

   Watch forThe extra charge for a long line run being skipped. It is a documented number in the installation manual, it is measured with scales, and omitting it quietly costs you capacity for the life of the system.

What does mini split installation cost?

A single-zone mini split installed typically runs $3,000 to $6,000, with each additional zone adding a few thousand more. Line run length, whether a condensate pump or electrical work is needed, and ceiling cassettes versus wall heads are the main variables.

See the full mini split installation cost guide - by material, size and region →

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