How Ducted Heating Works — Melbourne Guide

Melbourne’s cold winters — overnight temperatures regularly dropping to 5 to 8°C in the outer suburbs from May through August — make ducted heating one of the most important systems in a Melbourne home. The large majority of established Melbourne homes use a gas ducted heater: a central furnace that burns natural gas, transfers that heat to circulating house air through a metal heat exchanger, and distributes the warmed air through ceiling or floor ductwork to every room. Understanding how the system works helps Melbourne homeowners recognise normal operation, identify early fault signs, and know what is involved in annual servicing.

The Gas Combustion Cycle

A gas ducted heater uses controlled combustion of natural gas to produce heat. The process begins when the thermostat or wall controller signals a call for heat. The gas valve opens and the igniter lights the burner — either a standing pilot or an electronic ignition depending on the heater’s age and model. Brivis and Rinnai units produced since the mid-1990s use electronic ignition; older models may have a continuous pilot flame.

The burner generates a sustained flame in the combustion chamber. The heat from this flame transfers through the walls of the heat exchanger into the air stream passing on the other side. Combustion gases — carbon dioxide, water vapour, and small amounts of other combustion products — exit through the flue to the outside. The house air that has been warmed by the heat exchanger is then pushed into the duct distribution system by the blower motor.

Ignition sequence

On a modern Brivis or Rinnai Melbourne heater, the ignition sequence after a thermostat call is approximately: controller sends heat call → gas valve opens → spark igniter fires → flame sensor confirms ignition → blower motor ramps up → warm air distributes. If the flame sensor does not detect ignition within a set period, the controller performs a retry sequence and then may lock out with an error code. This is the most common cause of “no heat” faults — see our ducted heating not working guide for the full fault-finding sequence.

Heat Exchanger — The Critical Component

The heat exchanger is the most important component in a gas ducted heater from both a performance and safety perspective. It is a series of metal chambers — typically stainless steel or aluminised steel — through which combustion gases flow on one side and house air flows on the other. Heat transfers through the metal walls from the hot combustion side to the cooler house air side without the two gas streams mixing.

The critical safety point: if the heat exchanger develops a crack, perforation, or corrosion hole, combustion gases — including carbon monoxide — can pass through into the house air stream and be distributed through the duct system throughout the home. Carbon monoxide is colourless and odourless. This is why professional heat exchanger inspection is the primary safety function of the annual service.

Heat exchanger lifespan in Melbourne conditions

Most Melbourne gas ducted heater manufacturers rate their heat exchangers for a service life of 10 to 15 years under normal operating conditions. Factors that accelerate degradation include: operating the heater with a blocked filter or restricted return air (causing the heat exchanger to overheat); Melbourne’s coastal humidity on systems in poorly ventilated roof spaces; and infrequent servicing that allows acid-forming combustion byproducts to accumulate.

Air Distribution Through Ductwork

The blower motor draws return air from the home through the return air grille (typically in a central hallway ceiling or a main living area) into the heater body. This indoor air passes across the heat exchanger surface, picks up heat, and is pushed by the blower into the supply duct system. The supply ducts branch out through the ceiling or under-floor space to outlet grilles in each room.

Supply duct layout

In Melbourne homes, ceiling ducted heating outlets are the most common configuration — the heater sits in the roof space and flexible or rigid duct runs to outlets in every room ceiling. Under-floor ducted heating (floor outlets) is less common but found in some Melbourne homes, particularly those with concrete slabs that could not be easily retro-fitted with roof-space systems.

Return air requirements

A ducted heater’s performance depends critically on adequate return air — the volume of air returning to the heater to be reheated. The return air grille and its filter must be kept clear. A blocked filter is the most common cause of reduced performance and overheating in Melbourne ducted heating systems. See our filter replacement guide for Melbourne cleaning and replacement intervals.

Zoning — How Zone Control Works

Zone control allows Melbourne homeowners to direct heated air to specific areas of the home while closing off unoccupied rooms. This reduces gas consumption significantly by not heating rooms that are not in use — a Melbourne ducted heating system with effective zoning can reduce heating costs by 20 to 40 per cent compared to whole-home operation.

Zoning is achieved through motorised dampers — butterfly-shaped metal flaps installed in the duct runs serving each zone. The zone controller opens or closes these dampers based on which zones are activated. Simple zone systems use manual damper levers at each outlet; more sophisticated electronic zone controllers (fitted as standard or retrofit on modern Brivis and Rinnai systems) control motorised dampers automatically based on thermostat settings and occupancy.

Ducted Heating and Melbourne’s Winter Climate

Melbourne’s climate creates a clear seasonal heating demand. The city experiences cold winters with overnight temperatures regularly falling to 5 to 8°C in the eastern and outer suburbs (Ringwood, Doncaster, Frankston, Greensborough) and somewhat milder overnight lows closer to the bay. Cold fronts from the Southern Ocean can bring subzero overnight temperatures in outer suburban Melbourne in June and July. Ducted heating provides whole-home warmth from a single system — critical in Melbourne’s large brick houses where localised heating options struggle to maintain comfort across multiple bedrooms simultaneously.

Melbourne’s transition months (May and September) are when the ducted heater is used most intermittently — cold overnight and morning, warm during the day. This start-stop cycling is harder on ignition systems and heat exchangers than steady winter operation. Start-of-season faults — when the heater is first switched on in April or May after months of dormancy — are the most common service call pattern in Melbourne.

Key Maintenance Requirements

For the full annual service checklist and what each task involves, see our ducted heating annual service guide. For Melbourne 2025 service costs, see our service cost guide.

Frequently Asked Questions