Heat pump sizer

What size heat pump do you really need?

A 60-second, region-aware sizing tool — single room, whole house, or a multi-split system. No installer guesswork, no upselling.

NZ climate zones Watts-per-m² method Free & independent
Choose your mode

Most NZ households need multi-split if they have 2+ rooms to heat. It's the fastest-growing segment — and almost no other site sizes them properly.

Tell us about the room

Recommended size

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—Floor m²
—Heat load W
—Model class

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Indicative installed cost
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Add the rooms you want to heat
Rooms you want to heat

For each room, tell us the dimensions and how much glazing it has — we'll work out the heat load.

—Total kW
—Zones
—Cost band
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Why this matters: a multi-split outdoor unit is not just the sum of the indoor heads. Real installers apply a diversity factor (you don't run every room flat-out at once) and a combination ratio (manufacturers allow 100–130% indoor:outdoor). We do the maths the way installers do.
Configure your indoor heads

For each indoor head, tell us the room size and glazing — we'll auto-pick the right indoor kW and round it up to the nearest standard model.

—Indoor heads
—Sum indoor kW
—Outdoor kW
—Comb. ratio

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Estimated total system cost (supply + install)

Costs are NZ-typical mid-2026 ranges across Mitsubishi, Daikin, Fujitsu and Panasonic multi-split systems. Real quotes vary with brand, run lengths and electrical work.

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How we size it
  • Base heat load: NZ region × room m² × ceiling height multiplier
  • Adjustments for insulation level, glazing area and sun aspect
  • Multi-split: indoor sum × diversity factor (0.55–0.7 by head count), then matched to nearest standard outdoor unit, targeting a 110–120% combination ratio
  • Costs reflect typical mid-2026 NZ supply-and-install pricing across Mitsubishi, Daikin, Fujitsu and Panasonic

Heat pump sizing — frequently asked

As a rough NZ rule of thumb, allow 80–120 watts per m² of well-insulated living space. So a 30 m² lounge typically needs a 2.5–3.5 kW (heating capacity) heat pump. Cooler regions (Otago, Southland, central plateau) and poorly insulated rooms push you to the top of that range; modern, well-insulated Auckland homes sit at the bottom. Use the sizer above for a tailored number that factors in your region, ceiling height and insulation level.

No — oversizing is one of the most common (and most expensive) mistakes Kiwis make. An oversized heat pump short-cycles, runs at low efficiency, costs more to buy, costs more to run, dehumidifies poorly, and is noisier. Pick the size the room actually needs; modern inverter heat pumps modulate down very effectively when it's mild but cannot turn down past a certain floor.

Massively. A poorly-insulated room can easily need 50–80% more heating capacity than the same room with R3.6 ceiling insulation, R1.4+ underfloor and curtains over the windows. If you can possibly afford to insulate first (or apply for a Warmer Kiwi Homes grant), do — it lets you buy a smaller, cheaper, quieter heat pump that runs more efficiently for the next 15 years.

Sometimes — usually not. A single high-wall heat pump in the lounge will warm that room beautifully, but heat doesn't move well through doorways and hallways without help. For a whole-home solution either install separate heat pumps in each main living area and the master bedroom, or look at a ducted central system. Most NZ homes get the best results from 2–3 well-sized split units rather than one huge one.

Heat pump nameplates show two important kW figures. Heating capacity (typically 2.5–7 kW for splits) is how much heat the unit can deliver to the room — that's the number you size against. Power input (typically 0.5–2 kW) is how much electricity it draws to do that. The ratio between them is the COP — a COP of 4 means 1 kW of power becomes 4 kW of heat, which is why heat pumps beat resistive heaters by a huge margin.