Central Heating in Australian Residential Builds

What it is

Central heating warms a whole house from a single source instead of room by room space heaters. In Australian residential builds the three common systems are gas ducted, hydronic and reverse-cycle (heat-pump) ducted. Each one moves heat from a central plant to the rooms through ducts, pipes or both. The choice changes the design of the slab, the ceiling space, the gas connection and the electrical load.

Gas ducted heating

Gas ducted heating burns natural gas or LPG in a furnace, usually in the roof or under the floor. A fan blows air across a heat exchanger then pushes it through sheet-metal supply ducts to ceiling or floor outlets. Cool return air is drawn back to the furnace through a return-air grille.

The ductwork has to meet AS 4254.1 for rigid duct and AS 4254.2 for flexible duct. AS 4254.2 caps each piece of flex at 6 m and sets sealing classes A, B and C. Most residential supply ductwork is Class B. Insulation in ceiling voids is generally R1.5 or R2.0 depending on climate zone, called up under NCC Volume Two for ductwork in the thermal envelope.

Gas ducted is fast on warm-up and cheap to run when gas prices are low. The downside is on-site combustion. Victoria has restricted new residential gas connections from 1 January 2024 under planning Amendment VC250, which is reshaping how heating is specified south of the Murray.

Hydronic heating

Hydronic systems use a boiler (gas, electric or heat-pump) to heat water then circulate it through panel radiators, in-slab pipes or trench convectors. There is no ductwork, so no return-air design and no duct leakage to chase down.

In-slab hydronic needs to be designed into the slab before the pour, with cross-linked polyethylene (PEX-a) pipe tied to the mesh and pressure-tested before concrete goes down. Manifolds usually sit in a recessed cabinet inside the house. Heat-pump hydronic plants pair well with photovoltaic systems because the boiler can run on solar during the day and store heat in the slab.

Hydronic is quiet and comfortable and pairs well with high-mass construction. It is slower to respond than ducted and the upfront cost is higher.

Reverse-cycle ducted (heat-pump)

A reverse-cycle ducted system is an air-to-air heat pump with a single outdoor unit feeding a ducted indoor fan coil. It heats in winter and cools in summer, which makes it the default choice in most new Australian homes.

The refrigerant work needs a Refrigerant Handling Licence issued under the Ozone Protection and Synthetic Greenhouse Gas Management Act 1989. The electrical side falls under AS/NZS 3000 (the wiring rules). The ducts again follow AS 4254. Condensate drainage from the indoor coil has to discharge to a stormwater point or tundish, not to sewer, under most state plumbing regulations.

A modern inverter heat pump in heating mode usually returns several units of heat for every unit of electricity it draws, which is the energy case that has pushed Victoria, the ACT and many local councils toward all-electric new builds.

Energy and NCC interaction

NCC 2022 Volume Two raised the residential energy efficiency requirement from 6 stars to 7 stars NatHERS plus a new whole-of-home annual energy use budget. Central heating choice now sits inside that whole-of-home calculation. A reverse-cycle ducted system with a high seasonal coefficient of performance scores better than a gas furnace at the same heating output.

Duct location matters too. Ducts run in unconditioned roof spaces lose heat through the duct wall. Putting ducts inside the thermal envelope, or specifying higher R-value duct wrap, recovers that loss.

What to check on site

Look for: duct supports at the spacing the standard sets (not zip-tied to ceiling battens); flex duct pulled taut with no sags or kinks; return-air grille sized for the airflow the unit needs; condensate drain to stormwater not sewer; ARC licence number on the install paperwork for any refrigerant work; and a gas certificate of compliance from a licensed gas fitter for gas plant.