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Why most hydronic heating advice gets it wrong
Most hydronic content sells the comfort, the lovely even warmth, the warm tiles underfoot, and stops there. Comfort is real and worth having. But the articles rarely separate it from running cost, leaving people to assume hydronic is simply "expensive" or "luxury", when the truth is more useful: the comfort comes from the radiators and slab, the cost comes from whatever heats the water.
Get those two ideas apart and the decision clears up. You don't choose between "comfortable but pricey" and "cheap but harsh". You choose a comfortable delivery system, then pick an efficient source to feed it. The mistake is letting a gas boiler ride along by default when a heat pump would give the identical warmth for far less.
How hydronic heating costs work
A hydronic system has two parts: the emitters (radiators or in-slab pipes) that deliver the warmth, and the source that heats the water. The emitters set the comfort. The source sets the cost.
Gas boiler vs heat-pump source
A gas boiler burns fuel to heat the water at around 85 to 90% efficiency, and brings a daily gas supply charge. An air-to-water heat pump moves heat from outside air into the water, delivering roughly three units of heat per unit of electricity. Because hydronic water runs hotter than the air a normal aircon handles, the heat pump's efficiency is a bit lower than an air-to-air unit, but it still comfortably beats a gas boiler on running cost.
Steady, slow and worth timing
Hydronic systems heat slowly and hold warmth, so they tend to run longer, steadier hours than a blast of ducted air. That suits a heat pump well, and on a time-of-use tariff it rewards running the system through cheaper periods rather than only in the evening peak. The thermal mass of an in-slab system in particular can be "charged" with cheaper or solar power earlier in the day.
Boiler vs heat pump: the hydronic running cost
This calculator costs a winter of hydronic heating fed by a gas boiler versus an air-to-water heat pump, for the same comfortable warmth. Every figure also appears in the worked example below.
Hydronic source running cost
Same warmth, per winter. Edit any input.
Gas boiler at 88% efficiency; heat pump = heat ÷ COP × electricity rate. Excludes the gas daily supply charge, which widens the gas gap. Rates are editable defaults, not your plan.
Worked example (the calculator's default). 5 kW of heat, 8 h/day, 100 winter days, gas 4 c/MJ, electricity 30 c/kWh, heat-pump COP 3.2:
| Source | Energy used | Cost for the winter |
|---|---|---|
| Gas boiler (88% efficient) | ~16,360 MJ | ~$655 |
| Heat-pump hydronic (COP 3.2) | ~1,250 kWh | ~$375 |
Same comfortable warmth, about $280 less a winter from the heat pump, plus the gas supply charge of roughly $400 a year that only the boiler carries.
How Aussies overpay without realising it
Hydronic and gas got bundled together for years. Many buyers never realise a heat pump can feed the same radiators for far less.
An ageing boiler failing is the cheapest moment to switch the source to a heat pump, often missed in the rush to restore heat.
Hydronic holds heat well, so charging it earlier on a time-of-use plan dodges the priciest hours.
Zoning radiators or slab loops to occupied areas saves the same way it does on ducted systems.
The insider insight: the emitters outlast the source
Here's the detail that reframes the whole decision: in a hydronic system, the expensive, long-lived parts are the emitters and pipework, the radiators and the in-slab loops. Those can last decades. The source, the boiler or heat pump, is the shorter-lived, swappable component. So the comfort you paid for is largely permanent, while the thing that sets your running cost is the part you can change.
That means a household with gas-fed hydronic isn't stuck. When the boiler nears end of life, swapping in an air-to-water heat pump keeps every comfortable radiator and warm floor while cutting the running cost and shedding the gas supply charge. The luxury stays; only the expensive fuel leaves. Seen that way, hydronic isn't a "gas system", it's a comfortable delivery network waiting for the cheapest source you can bolt onto it.
What you should actually do
| Do this | Why it works |
|---|---|
| Choose (or switch to) a heat-pump source | Roughly three units of heat per unit of power, far cheaper than a gas boiler for the same comfort. |
| Treat a dying boiler as a source-swap moment | Keeps the radiators and slab, changes only the expensive-to-run part. |
| Run steady and charge earlier on time-of-use | Hydronic holds heat, so it rewards heating outside the evening peak. |
| Zone to occupied areas | Heating the rooms you use cuts cost without losing the comfort. |
| 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. For the broader picture see our home heating and underfloor heating guides.
Why this matters right now
With gas dear and air-to-water heat pumps increasingly common and rebate-eligible, hydronic comfort no longer has to come with a gas bill attached. Households with existing hydronic have a clear upgrade path that keeps the comfort and drops the cost.
The takeaway: buy the comfort once, choose the source for cost. A heat pump feeding your radiators gives the same warmth as a gas boiler for hundreds less a winter.
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.
| Air-to-water heat-pump efficiency (COP) | ~3 units of heat per unit of power |
|---|---|
| Gas boiler efficiency | ~85–90% (plus a daily supply charge) |
| Typical electricity rate | ~25–35 c/kWh [verify: your plan] |
| Typical gas rate | ~3–5 c/MJ [verify: your plan] |
| Typical gas daily supply charge | ~$1.00–$1.30/day [verify: your plan] |
| Recommended set point | 18–20°C |
| 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.