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Why most ducted heating advice gets it wrong
A lot of ducted heating advice still treats ducted gas as the natural default and reverse-cycle as the alternative. That reflects how things were a decade ago, not how the running costs stack up today. Gas lost the lead as prices climbed, and the comparison most guides skip, gas burning fuel versus reverse-cycle moving heat, is exactly the one that decides your bill.
The other thing they gloss over is zoning. Whether your ducts run on gas or reverse-cycle, heating the whole house to occupy one room is the dominant waste. Talk about the heat source without talking about zoning and you've answered half the question.
How ducted heating costs work
Two things drive the cost: the heat source and the volume of air you warm.
Gas vs reverse-cycle through the ducts
Ducted gas burns fuel in a central furnace and blows warm air through the house, at maybe 80% efficiency, plus the daily gas supply charge. Ducted reverse-cycle uses a heat pump to move warmth from outside air, delivering three to four units of heat per unit of power, and it reverses to cool in summer. For the same heat, reverse-cycle typically costs less than half as much to run, before you even count the gas standing charge.
Zoning is the multiplier
Zoning sets how much of the house each system actually heats. Heat half the home instead of all of it and you roughly halve the running cost, on either fuel. An unzoned ducted system is the most expensive heating in the house precisely because it conditions every room by default. Set points matter too: each degree above 18 to 20°C adds 5 to 10% to the energy used.
Ducted gas vs reverse-cycle: see the gap
This calculator costs a winter of ducted heating on gas versus reverse-cycle, and lets you set how much of the house you actually zone. Every figure also appears in the worked example below.
Ducted heating: gas vs reverse-cycle
Per winter, heating only. Edit any input.
Delivered heat = capacity × zoned share. Gas at 80% efficiency, 4 c/MJ; reverse-cycle = heat ÷ COP × electricity rate. Excludes the daily gas supply charge, which widens the gas gap further. Rates are editable defaults.
Worked example (the calculator's default). 6 kW system, zoned to 50%, 6 h/day, 100 winter days, gas 4 c/MJ, electricity 30 c/kWh, COP 3.8:
| System | Energy used | Cost for the winter |
|---|---|---|
| Ducted gas (80% efficient) | 8,100 MJ | ~$324 |
| Ducted reverse-cycle (COP 3.8) | ~474 kWh | ~$142 |
Less than half the running cost for the same warmth, and that's before the gas supply charge of roughly $400 a year that only the gas system carries.
How Aussies overpay without realising it
When the old gas furnace dies, swapping in another one locks in the dearer fuel for another 15 years instead of switching to reverse-cycle.
Heating the whole house to use one room can double the bill versus zoning to the rooms you're in.
If ducted gas is your only gas appliance, the daily supply charge is dead money for most of the year.
Each degree above 20°C adds 5 to 10% to the energy a ducted system burns through.
The insider insight: the install crew defaults to what they always fit
Ducted gas held the market for so long that it's still the reflexive recommendation in plenty of quotes, especially as a like-for-like replacement when a furnace fails. The path of least resistance is to fit what was there. But that default now points at the dearer-to-run system, and it often skips the chance to switch to reverse-cycle and drop the gas connection at the same time.
The savvy move is to treat a failing ducted gas unit as the moment to reconsider the whole setup, not just replace a box. Reverse-cycle ducting reuses much of the same duct network, adds cooling, qualifies for rebates and removes the gas standing charge. And whichever system you land on, insisting on proper zoning is what keeps a whole-home ducted system from being the most expensive way to heat the house.
What you should actually do
| Do this | Why it works |
|---|---|
| Favour ducted reverse-cycle over ducted gas | Less than half the running cost, plus summer cooling and no gas standing charge. |
| Zone the system and use it | Heating half the house instead of all of it roughly halves the cost. |
| Treat a dying gas furnace as a switch point | Reuses much of the ducting and is the cheapest time to change fuel. |
| Set 18–20°C, seal draughts | Each degree and every gap multiplies a whole-home heating bill. |
| In VIC, NSW, SA, QLD, ACT: compare plans against the DMO/VDO | A better rate lowers the cost of every heating hour. |
In Western Australia (Synergy) and the Northern Territory (Power and Water) there's no retailer to switch to. See our home heating guide for the source comparison and heating and cooling for the all-electric case.
Why this matters right now
With gas prices and supply charges high and rebates available for efficient electric systems, the running-cost case for ducted reverse-cycle over ducted gas is the strongest it's been. If your gas ducting is ageing, this is the cycle to switch.
The takeaway: reverse-cycle ducting heats for less, cools too, and drops a standing charge, and zoning decides whether any ducted system is affordable.
Frequently asked questions
Current figures — last updated 2026-06-13
All values in AUD and Australian units. Volatile figures change; check your own plan before relying on them.
| Ducted reverse-cycle heating efficiency (COP) | ~3–4 units of heat per unit of power |
|---|---|
| Ducted gas efficiency | ~80% (plus a daily supply charge) |
| Running-cost saving from zoning to half the home | ~50% |
| Typical gas daily supply charge | ~$1.00–$1.30/day [verify: your plan] |
| Recommended set point | 18–20°C |
| Typical electricity / gas rate | ~25–35 c/kWh · ~3–5 c/MJ [verify: your plan] |
| Reference price (NSW, SA, SE QLD / VIC) | AER DMO / ESC VDO [verify: current value] |
Sources: energy.gov.au, Australian Energy Regulator (DMO), ESC Victoria (VDO), manufacturer specifications.