How Gas Furnaces Work | Sierra Air

Understanding How a Gas Furnace Works

A gas furnace is perhaps the most popular type of central heating equipment in America. It looks simple on the outside, but it houses sophisticated assemblies of mechanical components designed to produce heat on demand.

Let’s explore how this HVAC unit works.

The Thermostat Sends a Request for Heat

The thermostat, whether manual, programmable or smart, monitors the air temperature. When it drops below a preset threshold, the thermostat sends a low-voltage electrical signal to the furnace, telling it to turn back on.

If your heating and cooling units are integrated into the same system, the thermostat should be on HEAT mode, so it knows it should talk to the furnace, not to the air conditioner.

The Gas Valve Opens to Send Fuel to the Burners

Once the signal from the thermostat is received, your furnace opens the gas valve to allow the natural gas to get into the burners and power the blower on.

The Air Is Heated

In the combustion chamber, the pilot light (or electronic ignition, if the furnace is a newer model) ignites the fuel. Heat is then created in a metal chamber, called the heat exchanger, where the air coming from the cold-air return is warmed up.

The Warm Air Gets Distributed Through the Ductwork

After the air’s temperature increases to a certain level as it flows around the heat exchanger, it’s then pumped into the hot-air plenum, which leads to the ducts. In an HVAC zoning system, there are dampers installed in the ductwork to stop the distribution of air to certain rooms.

Combustion Gases Are Vented to the Outside

Furnaces are designed so that combustion gases like carbon monoxide are directed to the flue, which stretches all the way to the roof. A high-efficiency gas furnace may use a sidewall power vent to expel gases outside through a draft fan installed at the end of an exhaust pipe.

Get the Best Out Your Gas Furnace With an Experienced Reno HVAC Expert

Sierra Air is the authority on all things HVAC. Call us at (775) 800-5500 to request service and gain access to top gas furnace solutions.