How much it costs to run a heat pump depends on how efficient it is at heating or cooling the air. Heating and cooling efficiencies are also a factor in calculating a heat pump’s energy ratings.

Heating efficiency is called COP (coefficient of performance). A good heat pump has a COP of 3 or more, meaning 1kW of energy produces 3kW of heat. Plug-in heaters all produce slightly less than 1kW of heat from 1kW of electricity, so a heat pump with a COP of 3 is three times more efficient than a standard heater.

Be aware, though, that because de-icing takes extra energy, a heat pump’s COP can be lower in near-zero temperatures.

Cooling efficiency is called EER (energy efficiency ratio). An EER of 3 or more indicates energy-efficient cooling.

You can figure out your hourly heat pump cost using the formula below. Your electricity unit cost will be on your power bill and should be somewhere around 26c.

Before you can choose a model of heat pump, you need to think about where the main unit will sit, and how you’ll circulate the conditioned air through your house.

Split systems

The simplest and most common option in New Zealand, split systems work best when located in the main living area of an open-plan home.

A split system has an exterior compressor unit connected to an interior ceiling or wall unit by copper refrigerant pipes and wiring.

The interior unit consists of electronic controls and a fan. It circulates air over finned tubing to either heat or cool it, depending on the settings.

Much of the installation cost for a split system comes from running the pipes and wires from outside to inside.

Multi-split systems

In a multi-split system, the exterior unit connects to more than one interior unit (for example, one in the living space and another in a bedroom).

Multi-split systems are usually cheaper than having multiple external units for different parts of the house, but there may be extra installation costs from longer piping runs.

The interior units can have separate remotes – but it isn’t possible to have one interior unit cooling while another is heating.

Ducted systems

Ducted systems feature a single, large-capacity interior unit mounted in the ceiling or under the floor. The conditioned air is pumped through insulated ducts to ceiling or floor outlets in several rooms in the house.

Ducted systems have the least visual impact of any heat pump system – just small flush vents in each room.

Because there’s some heat loss from the ducts, they are slightly less efficient than other systems. They’re also expensive to install.