How Does a Furnace Work? : The Science Behind Heating Your Home


Furnaces are among the most important appliances in your home, responsible for heating them during those cold winter months. How does a furnace work? Let’s take a closer look at the science behind this essential appliance!

If you need a new furnace or some repairs, Landmark Air Canberra is the company for you. We offer excellent gas heating services, and we’re dedicated to keeping your home warm all winter long!

How a Furnace Works?

Although there are minor variations, the basic operation of all gas furnaces is the same. Exhaust fumes from the heat exchanger are expelled through the flue gas vent when natural gas is burnt.

Once the air has passed through the heat exchanger, a blower fan distributes it throughout your house. The thermostat switches off the furnace when it senses the correct temperature.

A draft inducer fan is used in modern furnaces to remove the exhaust.

The use of a forced draft further improves the effectiveness of the system. To condense water vapour, condenser furnaces employ a two-stage heat exchanger, absorbing even more heat from the burning fuel.

Efficiency and Rate

A few or yearly fuel usage efficiency is used to grade furnaces. In order to get this value, we divide the amount of fuel consumed by the amount of heat generated.

This means that just 70 per cent of the fuel is used to generate usable heat in older furnaces. High-efficiency condenser furnaces may reach up to 90 per cent efficiency, whereas mid-efficiency furnaces are roughly 80 per cent efficient. Single-stage and dual-stage furnaces are both available.

Modern vs. Traditional Furnace

When using a single-stage furnace, you get complete heat or no heat. When less heat is required, the speed of a two-stage furnace can be lowered. A quieter and more stable temperature may be achieved thanks to this.

System-wide safety switches ensure that the furnace shuts off if something goes wrong. The furnace will shut out if a switch is tripped.

Attempts to start the furnace will be made multiple times until a hard lockout lasting for up to an hour occurs. When a lockout occurs, the furnace uses flashing lights as a code to identify the shutdown’s cause.

Check your furnace’s handbook to determine what each of these codes indicates.


Voltage is supplied to the control board when the thermostat makes a heat request. Draft inducer fan then draws new air into the burner for a more efficient and clean burn.

The pressure switch will close when the draft motor achieves maximum speed, enabling the procedure to proceed. The pressure switch guarantees that the furnace may be safely operated by ensuring sufficient airflow inside the heat exchanger.

The switch will remain open if the pressure is low, preventing the furnace from starting.

A steady stream of electricity is transmitted to the heated surface if the pressure is adequate. Igniter. A spark igniter may be used in some furnaces.

The gas valve opens, and the burners are ignited after the igniter has heated up. With safety switches still in place, the flames will keep going.

The gas will be turned off if the flame sensor does not detect it after seven seconds.

For the heat exchanger to warm up, the blower fan is held back from operating when the burner is on. As a result, no cold air is circulated by the furnace.

The air is then circulated throughout your house by a blower fan, which blows it across the heat exchanger. A limit switch monitors the air moving across the heat exchanger to prevent the furnace from overheating.

The heat extender may overheat if the system overheats due to ventilation constraints. As a result, changing the furnace filter every three to six months is required.

Contact Us

Now that you understand how a furnace works, If you need a new or replacement furnace and want to know more about how a furnace works, be sure to call Landmark Air Canberra. We can help you find the best furnace for your home and provide expert installation and service.

Call us at (02) 6189 2972  to learn more! We’re always happy to help our customers in any way we can.


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