Hydronic Costs 4x a Heated Room. Whole-House Electric Slab Runs Dearer Than Gas Hydronic

Underfloor heating vs hydronic: the two prices cover different jobs

At Going Rate's prices, a hydronic heating system ($21,500) costs over four times as much as a typical electric underfloor heating job ($5,000). Going Rate prices underfloor heating by floor area, so a typical job is a room or zone, such as a bathroom, rather than a whole house. The hydronic price covers wall panels or pipes laid in the slab, run from a boiler or heat pump, and is usually meant to heat much more of the house.

Installers price the two by area in different ways. Comfort Heat, an underfloor heating seller, writing on ArchiPro, puts electric underfloor heating at $80 to $200 per square metre installed, and hydronic at $150 to $250 per square metre for pipe and screed, plus the heat source. The same vendor quotes $30,000 to $50,000 for a complete hydronic underfloor system, with pipe, manifold and heat pump, in a new build of around 200 m². Those are vendor figures, and they show how fast a floor heating price grows once it leaves the bathroom.

The terms blur too. NSW's BASIX rules define in-slab heating as hot water pipes or electric wires or mats laid in a concrete slab or topping, and exclude on-floor systems laid over a slab under tiles or carpet. Sustainability Victoria's running costs below are for whole-house in-slab systems, so they describe a far bigger job than a heated bathroom floor.

Hydronic heating running costs against a heated slab

Sustainability Victoria (SV), which has since closed, published annual running costs for common central heating systems. Its last tables survive in archived copies and use mid-2025 Melbourne default-offer tariffs, an average pre-2005 house heated to 20°C and unzoned systems, and they exclude fixed supply charges. For a 160 m² house, SV puts electric in-slab at $3,366 a year, gas hydronic at $1,915 (European A rating, 92%) to $2,097 (C rating, 84%), gas ducted at $2,299 to $2,921, and multi-split reverse-cycle air conditioning at $923 to $1,230. Electric in-slab is the dearest central system in the table. Ducted heating ($10,800) costs about half as much as a hydronic system to install at Going Rate's prices.

On those archived mid-2025 figures, whole-house electric in-slab costs about 1.76 times as much to run as A-rated gas hydronic. The ratio holds across SV's house sizes, on the same assumptions. In its 100 m² small house, in-slab is $2,104 a year against $1,288, about 1.63 times. In its 220 m² large house, it is $4,629 against $2,522, about 1.84 times.

YourHome, the Australian Government's housing guide, says electric in-slab heating generally has the highest energy use of any heating system. The ACT Government says it is usually the most expensive heating system to run. A resistive cable turns one unit of electricity into one unit of heat, and the ACT Government lists electric element heating at 100% efficiency against 250% to 600% for reverse-cycle heat pumps.

Why electric floor heating is sold room by room

SV's archived whole-house in-slab bill of $3,366 a year (160 m² pre-2005 Melbourne house, mid-2025 tariffs, excluding supply charges) comes to about two-thirds of a typical electric underfloor job ($5,000) at Going Rate's prices. Put the other way, about 18 months of whole-house slab running costs as much as that one install. We set a whole-house running cost against a room-sized install to show the scale of a whole-house electric slab. Neither figure describes the running cost of a heated bathroom.

Room-sized jobs cost far less to run. Comfort Heat, via ArchiPro, says a 5 m² bathroom with electric underfloor heating running 4 hours a day costs around 65 to 90 cents a day, and less than $65 for a whole winter. That is a vendor figure. It explains why electric floor heating suits a cold tiled bathroom and struggles as the main heater for a house.

YourHome gives a second reason. In-slab systems are slow to warm and cool because of the slab's thermal mass, which makes them unsuitable for houses that need heat only occasionally or for short periods. NSW BASIX calls electric slab heating a greenhouse-intensive technology. SV's archived mid-2025 figures put its 10-year emissions for a 160 m² pre-2005 Melbourne house at 69.4 tonnes, against 31.1 tonnes for A-rated gas hydronic and 19.8 tonnes for a 2-star ducted reverse-cycle system.

The running-cost gap between slab and gas hydronic is narrowing

SV's December 2023 edition, with figures last updated in June 2023, put whole-house electric in-slab at $3,944 a year and A-rated gas hydronic at $1,657 for the same 160 m² pre-2005 Melbourne house, excluding supply charges. That made in-slab about 2.38 times as dear to run. In the archived mid-2025 figures, in-slab had fallen to $3,366 and gas hydronic had risen to $1,915, bringing the ratio down to about 1.76. SV said electricity prices had fallen slightly since its August 2024 update while natural gas prices rose.

The archived figures probably understate gas costs in 2026. SV's 160 m² table assumes gas at 3.41c/MJ. EnergyAustralia's Victorian general residential standing offer from 1 July 2026, in the AusNet Central zone, charges 4.98c/MJ for the first 100 MJ a day in its 1 June to 30 September peak, the heating months, falling to 3.07c/MJ for the heaviest use. SV also leaves out supply charges. On our arithmetic, the same offer's 158.4c a day supply charge comes to about $580 a year for a household that keeps gas only for heating. Electricity has moved less. The Essential Services Commission's 2026-27 Victorian Default Offer flat usage rates run from 25.96c a kWh (CitiPower) to 31.98c (AusNet Services) including GST, either side of SV's 29.2c peak rate, and the average Victorian Default Offer household bill fell $84, or 5%, to $1,591 a year.

Worked example (our arithmetic on SV's archived mid-2025 figures). Swapping whole-house electric in-slab for A-rated gas hydronic in SV's 160 m² pre-2005 Melbourne house saves $1,451 a year, excluding supply charges. Paying for a hydronic heating system ($21,500) out of that saving would take about 15 years, or about 17 years with a C-rated boiler. The Going Rate price is a typical job and may not match a 160 m² whole house. Gas supply charges and 2026 gas tariffs above SV's rate would stretch the payback, servicing is not counted, and the example only applies to an existing house that already runs whole-house slab heating.

Victorian gas rules: who can still choose gas hydronic

Victoria's 2024 rule covers only homes that need a planning permit. Planning amendment VC250 stops new dwellings, apartments and residential subdivisions connecting to reticulated natural gas where the planning permit application was lodged on or after 1 January 2024. It does not cover a new dwelling that needs no planning permit, or bottled LPG. The broad rule arrives on 1 January 2027, when the Victorian Government says all new homes must be built all-electric, whether or not they need a planning permit.

Existing homes keep their options. Energy Victoria says owner-occupiers face no requirement to replace gas space heating, though from 1 March 2027 a failed gas hot water system must be replaced with an electric one. In rentals, from 1 March 2027, a heating appliance that breaks and cannot be repaired must be replaced with an efficient reverse-cycle air conditioner in the main living area. The ACT Government has commenced a regulation preventing new fossil fuel gas network connections, and says at least 90% of the roughly 3,000 new connections a year are for new homes.

For a new Victorian home, that means hydronic heating will need an electric heat source such as a heat pump. SV's archived tables have no heat-pump hydronic row, and neither YourHome nor the ACT Government gives a running cost for one. Solar Victoria says only that it involves a higher initial investment for purchase, installation and operation than reverse-cycle air conditioning. Energy Victoria consulted from 23 April to 22 May 2026 on a new Victorian Energy Upgrades activity to replace gas hydronic boilers with heat-pump hydronic, which is a proposal and not yet a discount.

Climate and insulation move the bill more than the system

SV's archived tables scale by climate. It says to multiply the Melbourne figures by 1.5 for a cold climate such as Ballarat and by 0.8 for a warm one such as Mildura. On our arithmetic, that puts whole-house in-slab at roughly $5,000 a year in Ballarat and A-rated gas hydronic at roughly $2,900, for the same 160 m² pre-2005 house at mid-2025 tariffs, excluding supply charges.

House quality matters more. SV says to multiply its Melbourne figures by 0.4 for a 5-star house and by 0.3 for a 6-star house. In a 5-star 160 m² house that would bring in-slab to roughly $1,350 a year and A-rated gas hydronic to roughly $770, on our arithmetic at the same archived mid-2025 tariffs. SV's multipliers describe houses built to those ratings. They do not promise what an insulation retrofit will save in an older house.

For scale, ceiling insulation ($3,500) costs about a sixth of a hydronic system ($21,500) at Going Rate's prices, and a broader insulation job ($3,950) a little under a fifth. In NSW, BASIX requires insulation at the edge of every slab with in-slab heating, and underneath any suspended slab, in all climate zones.

Servicing and safety for gas hydronic and electric floors

Gas hydronic needs a gasfitter. Energy Safe Victoria recommends servicing all gas heaters, central heating units included, at least every two years, including a test for carbon monoxide leakage. Budget for a typical gas heater service ($330) at that interval. A boiler service may differ, since the Going Rate price covers gas heaters generally.

Electric underfloor heating has no burner to service, but it needs a properly protected circuit. HIA says the AS/NZS 3000:2018 wiring rules require RCD protection on all final subcircuits in new domestic work and alterations, which covers a new underfloor heating circuit.

The carbon monoxide deaths Energy Victoria cites involved open-flued gas space heaters, and since 10 August 2022 Victoria has banned new or replacement installations of open-flued heaters that do not meet the revised standard. Energy Victoria links those heaters to the deaths of Chase and Tyler Robinson in 2010 and Sonia Sofianopoulos in 2017. Hydronic boilers are a different appliance, though the two-yearly service and CO test still apply.

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