What size heat pump do I need?

Capacity is sized from the room, not the appliance: floor area × an allowance in watts per square metre, scaled for ceiling height. The result is a range in kW, and the models registered for sale in New Zealand at that capacity.

Where to find the numbers

Measure the room at floor level, length by width, and the ceiling height. Room type is a judgement: a shaded, well-insulated bedroom sits at the low end; a west-facing living room with large windows sits at the high end.

What the figure is based on

The watts-per-square-metre allowances are the conventional sizing range (100 to 160 W per m² against a 2.4 m ceiling), not a heat-load calculation. A proper load calculation accounts for insulation, glazing, orientation, air changes and climate zone, and an installer should do one before purchase. Undersizing means the unit runs flat out; oversizing means short cycling and poor humidity control.

What changes the cost

• Insulation and glazing move the requirement more than floor area does; the same room can differ by a whole capacity class.
• Orientation: a west-facing room takes the afternoon sun and needs more capacity than a south-facing one of the same size.
• Ceiling height changes the air volume being conditioned, which is why the allowance is scaled against a 2.4 m reference.
• Open plan: an unclosed space is not the room you measured; size for the volume the unit actually has to hold.
• Climate zone changes both the load and the label figure, which is why the register reports energy use by zone.

Compare heat pumps by energy use and running cost to see every model behind this figure.

Once you know the size, see what a heat pump of that size costs to run.

For a specific model or any other appliance, use the electricity cost calculator.