What Is a Heat Pump? How It Works, and Why It Uses So Little Power

What is a heat pump?

A heat pump is a device that moves heat from one place to another rather than generating it. That is the whole idea, and it is why the name matters: it pumps heat, like a water pump moves water, instead of burning fuel or glowing an element to create heat from scratch. Because moving heat takes far less energy than making it, a heat pump delivers several times more heating or cooling than the electricity it consumes. You already use them: a fridge is a heat pump that moves heat out of its cabinet, and a reverse cycle air conditioner is a heat pump that moves heat into or out of your home.

How does a heat pump work?

How does a heat pump work? It circulates a refrigerant through a cycle of four steps. The refrigerant absorbs heat from a source (the outside air, even when cool), a compressor raises its temperature, it releases that heat where you want it (inside the room, or into your water), and then it expands and cools to start again. In heating mode it gathers warmth from outside and delivers it indoors; a reverse cycle unit can run the cycle the other way to remove heat in summer. The clever part is that the electricity only drives the compressor and fans; the bulk of the delivered heat is gathered free from the environment, which is why the output exceeds the electrical input.

COP: the number that explains everything

A heat pump's efficiency is its Coefficient of Performance, the ratio of heat delivered to electricity used. A COP of 4 means four units of heat for one unit of power, an effective efficiency of 400%, which is impossible for any device that makes heat but routine for one that moves it. Modern home heat pumps sit around a COP of 3 to 4.5. This single number is why a heat pump beats every resistive heater, which is stuck at a COP of 1, and why it undercuts gas on the cost of delivered heat.

Heat pump power consumption

Heat pump power consumption is low for the comfort delivered precisely because of the COP. To work out the electricity a heat pump draws, divide the heat you want by its COP: 4 kW of heating from a COP-4 unit needs just 1 kW of power. The calculator below turns a heat or cooling demand into the electricity used and the cost, and shows what the same job would cost with a resistive device. Every figure also appears in the table beneath.

Where heat pumps fit in an Australian home

A heat pump powers three of the biggest jobs in the house. For space heating and cooling, a reverse cycle air conditioner, split or ducted, is a heat pump that does both seasons from one unit. For hot water, a heat pump hot water system heats your water for about a third of the energy of an electric tank, with CO2 units such as Reclaim Energy among the Australian options. For homes with radiators or underfloor pipes, an air-to-water heat pump can replace a gas boiler as the hydronic heat source. The same technology, in three forms, covers heating, cooling and hot water, the bulk of a home energy bill.

How Australians misjudge heat pumps

The common doubt is that a heat pump cannot work in the cold. Modern units extract usable heat from air well below zero, and their COP only eases as it gets very cold rather than collapsing, so for the vast majority of Australian conditions they heat efficiently all winter. The second misjudgement is buying on price and overlooking the COP, which is the number that sets the running cost; two units at the same price can differ markedly in what they cost to run because their COP differs. The third is not claiming the rebates, which for heat pump hot water and reverse cycle heating can run into the thousands.

The insider insight: you already trust a heat pump

People hesitate over heat pumps as if they were unproven, while a heat pump has been humming away in their kitchen for decades: the fridge. A fridge is a heat pump that moves heat out of its insulated box and dumps it into the room, running reliably for fifteen years. A home heat pump is the same physics pointed at your living room or your hot water tank. Once you see that the technology you already rely on to keep food cold is the technology now asked to keep you warm, the hesitation falls away. The only real question left is the COP and the rebate, not whether the idea works.

What you should actually do

When you next replace heating, cooling or hot water, default to a heat pump and compare units on their COP, not just their price, since the COP sets the running cost. Use a reverse cycle system for space heating and cooling, a heat pump hot water system in place of an electric tank, and an air-to-water heat pump as a hydronic heat source. Claim the STC discount and any state rebate through an accredited installer.

Because every heat pump runs on your electricity rate, households in VIC, NSW, SA, QLD and the ACT can compare plans against the DMO or VDO reference price, and pairing a heat pump with rooftop solar makes its cheap heat cheaper still. See our guides to the most energy efficient heater, water heaters and heating and cooling for each application.

The bottom line

A heat pump moves heat instead of making it, which is why it delivers three to four times more warmth or cool than the power it uses, and why its power consumption is so low for the comfort it gives. It is the technology behind your fridge, your air conditioner and the cheapest hot water available. Compare units on COP, claim the rebate, and let the physics do the saving.