A ducted reverse cycle system can seem like magic — one electric box outside that somehow heats your whole home in winter and cools it in summer, without burning anything. But the principle behind it is simple and well understood: it moves heat rather than making it. Understanding how it works helps you see why it is so efficient, why it keeps working in a cold Melbourne winter, and what the parts of your system actually do. This guide walks through it step by step.
The Heat Pump at the Heart of It
At the core of every ducted reverse cycle system is a heat pump — the same technology in your fridge, scaled up and made to work both ways. The key idea is that a heat pump does not create heat by burning gas or running an electric element. Instead, it moves heat from one place to another using a refrigerant that absorbs heat when it evaporates and releases heat when it condenses.
This is why heat pumps are so efficient. Creating heat by burning fuel can, at best, turn one unit of energy into one unit of heat. Moving heat is different: by using a little electricity to pump heat that already exists, a heat pump delivers several units of heat for each unit of electricity it uses. That ratio is the system’s efficiency, and it is the reason ducted reverse cycle is central to Melbourne’s shift to electric homes.
The Refrigeration Cycle
The heat pump moves heat using a continuous four-stage loop called the refrigeration cycle. A refrigerant circulates around the system, changing between liquid and gas, and at each stage it either absorbs or releases heat. The diagram below shows the cycle in heating mode — pulling heat from the cold outside air and delivering it into your warm home.
Following the loop: the compressor (1) squeezes the refrigerant gas, raising its pressure and temperature. The hot refrigerant flows to the indoor coil (2), where it condenses and releases its heat into the air being blown into your home. The now-cooler liquid passes through the expansion valve (3), which drops its pressure and temperature sharply. The cold refrigerant then reaches the outdoor coil (4), where it absorbs heat from the outside air and evaporates — before returning to the compressor to start again. The hot, high-pressure side of the loop is shown in red; the cold, low-pressure side in blue.
Heating Mode vs Cooling Mode
The clever part — and what makes it “reverse cycle” — is that the same system runs this loop in either direction. A component called the reversing valve changes the direction the refrigerant flows, which swaps the jobs of the two coils.
In heating mode (shown in the diagram), the outdoor coil absorbs heat from the outside air and the indoor coil releases it into your home. In cooling mode, the valve reverses everything: now the indoor coil absorbs heat from inside your home (cooling the air), and the outdoor coil rejects that heat outside. It is the same hardware and the same refrigeration cycle — simply flipped. This is how one system delivers both heating and cooling, and why a ducted reverse cycle replaces both a heater and an air conditioner.
Distributing Air Through the Home
Heating or cooling the air is only half the job — it has to reach every room. In a ducted system, the indoor unit (the fan coil) sits hidden in the roof space and connects to a network of ducts. A fan draws air from the home through a return air grille, passes it across the indoor coil to heat or cool it, and pushes the conditioned air out through supply ducts to outlets in each room’s ceiling.
This whole-home distribution is the defining feature of a ducted system, and what separates it from a split system that conditions only one area. The ductwork is sized and balanced so each room receives the right amount of air, and the same ducts carry warm air in winter and cool air in summer. In many Melbourne homes that already have ducted gas heating, this existing ductwork can be reused for a ducted reverse cycle system — see our adding cooling to existing ducts guide.
Zoning and Control
Because a ducted system serves the whole home, it would be wasteful to condition every room all the time. Zoning solves this. The ductwork is divided into zones — groups of rooms — each with a motorised damper that opens or closes to direct air where it is wanted. A zone controller lets you choose which areas are conditioned, so you can heat or cool the living areas during the day and the bedrooms at night, without running the whole house.
Zoning is the single biggest lever on running cost in a ducted system, and a major reason modern ducted reverse cycle is economical to run. By only conditioning the rooms in use, the system does less work and uses less electricity. See our zoning explained guide for how to set zones up well.
Efficiency and COP
The efficiency of a heat pump is measured by its Coefficient of Performance, or COP — the ratio of heating or cooling output to the electricity it consumes. A COP of 4 means the system delivers four units of heating for every one unit of electricity, because it is moving heat rather than generating it. Ducted reverse cycle systems typically achieve a COP of 3 to 5, depending on the model, the conditions and how well it is zoned.
This is what makes reverse cycle so much more efficient than older forms of electric heating, and competitive with — often cheaper than — gas. The higher the COP and the better the zoning, the lower the running cost. Combined with the removal of the gas supply charge when a home electrifies, it is why so many Melbourne households are making the switch. See our running costs guide for what this means in dollars.