Ducted gas versus reverse cycle
For thirty years ducted gas was the default way to heat a house in southern Australia, and for most of that time it was the right call. It is not any more, and the size of the gap surprises people.
What each costs
| State or territory | Ducted reverse cycle | Multi-split | Ducted gas | Electric heaters |
|---|---|---|---|---|
| New South Wales | $1,188 | $820 | $1,004 | $387 |
| Victoria | $1,450 | $1,006 | $1,906 | $834 |
| Queensland | $1,002 | $688 | $579 | $132 |
| South Australia | $1,800 | $1,254 | $1,579 | $814 |
| Western Australia | $1,369 | $949 | $1,698 | $444 |
| Tasmania | $1,870 | $1,304 | no gas | $1,243 |
| Australian Capital Territory | $2,635 | $1,846 | $2,804 | $1,661 |
| Northern Territory | $1,858 | $1,295 | no gas | $0 |
A 160 m² pre-2005 house, heating and cooling for a full year, at each state's reference rates. Cheapest in each row is in bold. Note that the ducted and multi-split figures are not doing the same job — see the conditions column in the calculator.
Reverse cycle wins on running cost in every state with mains gas. The reason is arithmetic rather than opinion: a gas furnace can never deliver more energy than it burns, and a heat pump routinely delivers three to four times what it consumes because it is moving heat rather than making it.
The margin varies far more than that suggests, though, and it is worth knowing where you sit. Replacing ducted gas with ducted reverse cycle in a 160 m² pre-2005 house saves about 53% in Western Australia and 31% in Victoria, but only about 13% in the ACT — dear electricity erodes a heat pump's advantage, and Canberra has the dearest electricity of any state with mains gas. Everywhere it is a saving; in Canberra it is a modest one.
The 86% on the compliance plate is not what reaches the room
A 6-star ducted gas furnace is rated at around 86% efficient. That figure is measured at the burner. By the time the air has travelled through ducts in an uninsulated roof space, what actually arrives in the room is well under 80% of the gas you paid for.
Our model uses 78%, which is the figure that makes it reproduce Sustainability Victoria's published running costs across all three house sizes. That is not a guess about duct losses — it is what the observed costs imply once the gas price and the heating load are known.
The comparison people make in their heads is 86% against a heat pump's "300%". The real comparison is 78% against an effective seasonal figure of around 300 to 380% depending on the star rating and the climate. The gap is larger than the marketing on either side suggests.
Then there is the connection charge
The same trap as hot water. A gas connection costs $0.80 to $0.96 a day — around $300 to $350 a year — before a single megajoule is burned. If heating is the last thing keeping you on gas, replacing it saves that entire charge on top of the fuel saving.
That is what makes the all-electric decision so much better than a system-by-system comparison suggests. Swapping ducted gas for reverse cycle saves the running cost difference. Swapping ducted gas and the gas hot water and the cooktop saves the running cost difference plus the whole connection charge, and only the last of the three has to happen for that saving to land.
Our hot water calculator asks what else you use gas for, and this is why.
What about emissions?
Unlike hot water, this one is not close, and it is worth spelling out why the two modules reach different conclusions.
A hot water heat pump has an effective coefficient of performance of about 2.2, because it is lifting water 45 degrees and losing heat from a tank all day. A space heating reverse cycle system runs at 3.0 to 3.8, because it is lifting room air a much smaller number of degrees. That difference is enough to flip the emissions comparison: a gas water heater can beat a hot water heat pump on today's grid, and ducted gas heating cannot beat reverse cycle heating anywhere in Australia.
Even in Victoria, with the dirtiest grid in the country at 0.78 kg of CO₂-equivalent per kilowatt hour, reverse cycle heating produces materially fewer emissions than ducted gas for the same warmth. Run the numbers yourself in the calculator.
What we would actually do
- Gas ducted has failed, and the ducts are sound? Replace it with ducted reverse cycle. Reusing the ductwork removes a large chunk of the installation cost and this is the cheapest moment you will ever get.
- Gas ducted still works? There is a real running cost saving in switching, but not usually enough to justify scrapping a working system on cost alone. Plan for it at end of life and put the money into insulation meanwhile — that saves more than the system change does.
- Building or renovating? All-electric, and do not run the gas connection at all. Connecting gas costs $1,000 to $2,500 before you buy a single appliance, and every incentive scheme in the country now points the other way.
- In Victoria? Check the Victorian Energy Upgrades program before you buy. Replacing a ducted gas system with reverse cycle attracts substantial support there, which changes the arithmetic on replacing a working system.
Frequently asked questions
Does reverse cycle heating work when it is really cold?
Yes, throughout Australia. Efficiency falls as the outside air gets colder, because there is less heat in it to move, but every Australian capital including Hobart and Canberra sits well within the operating range of a modern inverter unit. The concern is imported from northern hemisphere climates that routinely see minus twenty, which no Australian capital does.
Is gas heating warmer or more comfortable?
The common complaint is that reverse cycle air feels less warm, and there is something to it: gas ducted typically delivers air at a higher temperature, while a heat pump delivers a larger volume of cooler air. The room reaches the same temperature either way. If the sensation matters to you, that is a legitimate preference, but it is a comfort argument rather than a heating one and it is worth knowing that is what you are paying for.
How much does it cost to disconnect gas?
Abolishing a connection typically costs a few hundred dollars and varies by distributor; some charge nothing to simply remove the meter. Against $300 to $350 a year saved it pays for itself quickly, but get a figure from your distributor first because it is not standardised.
Will my switchboard handle reverse cycle?
Usually, but it is the most common surprise cost in a gas-to-electric conversion. A ducted reverse cycle system needs a dedicated circuit and older switchboards sometimes need upgrading, which can add $800 to $2,500. Ask for it to be assessed at quote stage rather than discovered on installation day — it is not included in the installed cost ranges on this site.
Can I keep gas for cooking and go electric for heating?
You can, and plenty of people do, but understand what it costs: keeping the connection for a cooktop means still paying the daily supply charge, which is most of what you would have saved. If the cooktop is the only thing left on gas, an induction cooktop is worth pricing at the same time — that is the change that lets the connection go entirely.