How Does Ducted Central Heating Work?

If you are unfamiliar with how a gas ducted system works, or simply wish to know more about the options that are available we hope the following simply explains how the system works and provides options you may wish to consider.

Ducted Central Heating

A gas ducted central heating system is where heated air is distributed throughout the home by a network of ducts, usually in the roof cavity or under the floor. Air is heated in a heat exchanger, which is heated by clean burning gas. The warm air enters each room through an outlet located in the floor, ceiling or wall.

The heated air is then re-circulated through an inlet (Return Grille) that is normally centrally located and may be in the wall or ceiling. This air is then passed back over the heat exchanger, heated and re-circulated.

With heating a house we normally required 5 air changes per hour to keep warm. With cooling, the number of air changes increases to 10. The size of the heat exchanger is determined therefore by the size of the house, heating or cooling, insulation, building materials, windows and local climatic conditions.

We use our Bonres® system to help guide us with furnace size selection and the required number of duct outlets. All 4 and 5 star Bonaire units have high tech modulating fan technology that delivers whole-of-home heating efficiently and quietly.

Key Components

Heat Exchanger (or Furnace)

The heat exchanger is a gas fired burner that heats the air as it passes over the burners through air tubes. These are specifically designed to ensure the efficient transfer of heat from the gas burner to the passing air.

Heat exchangers vary in terms of:

Efficiency - Bonaire has 3 platforms:

  • MB4 – 4 star efficiency (90%)
  • MB5 – 5 Star efficiency (95%)
  • MB6 - 6 Star efficiency

Adjusts the gas rate as the home approaches the set temperature therefore enhancing the energy efficiency. Our Bonaire series MB4 and MB5 have the ability to reduce heat to 10% allowing you to further reduce your energy bills if you only want to heat a small area of your home.

Size (Energy)
Different size homes, climatic conditions and building materials affect the amount of energy required to heat the home. Bonaire units come in sizes from 14kW; 20kW; 30kW and 30kW extra-air to suit all conditions


Flexible ducting is used to transfer air to and from the furnace to outlets in the home. Ducting is designed with thermal properties to minimise any heat loss in the transfer. It is also well protected with a fire retardant jacket for the safety of your home.

Grilles & Vents

Often referred to as the outlets or inlets, the grilles and vents are the termination points of the ducting in your home, and critically they must be aesthetically pleasing. Therefore a wide range of air grilles, ceiling diffusers and floor and wall vents are available.

A typical installation within the home will have a return air grille in a central point, with the outlet vents on the extremities of the home. The effect of this is that the warm air is initially distributed to the extremities of the room and the air is drawn back to the return air grille before being re-circulated.

Typically though, vents can be placed in areas that work within the specific room’s design making allowances for windows, beds etc.

Zone Dampers

The Bonaire system can be fitted with multiple zones, which are mechanically driven shut-off ducts. These stop the flow of air.

When designing your home’s duct plan, there may be areas that are often not used e.g. guest or spare bedrooms, and by installing a zone damper you can stop the flow of warm air to those areas, thereby reducing your running costs.


Allow you to remotely set and control the furnace’s operation. Controllers typically allow 24/7 programmability, and also have set functions such as zone operations, summer breeze functionality and heating and cooling (if installed).

Controllers can be either wall mounted or remote (wireless). They also aid fault finding and help service people set-up the furnace in terms of fan speeds and temperature settings.