How a gas furnace works:
The heating cycle starts when the thermostat senses that the room temperature is below the setpoint. On newer units, this causes an inducer fan to pull air through the unit establishing adequate combustion airflow. After proper airflow is verified, the gas valve is opened allowing gas to flow. The gas flows through the burners where it is ignited by a spark or the heat from the ignitor. (Older units have what is called a standing pilot which is a small flame that burns constantly to light the gas.)
After the unit senses the flame is lit, the spark or ignitor is turned off. A
flame sensor is on the opposite of the ignition sensing proper flame roll-out, if improper igition is sensed, system will end ignition sequence and shutoff. Normally, the gas will burn for approximately two minutes before the blower is started. This prevents blowing cold air out the vents at the start.
After the preset time or at a set temperature, the blower motor is energized and air is blown over the heat exchanger. The air is heated and supplied to the duct system.
How an electric furnace works:
Electric furnaces produce heat from an element which is made up of special wires. Electricity flows through the element. These units are 100% efficient and use all of the electricity to produce heat. The size of the units is expressed kilowatts instead of BTU/HR.
When a thermostat calls for heat, a relay energizes the heating element and indoor blower motor. Some units use multiple heating elements. These units have relays that turn on the other heating elements when more heating is called for.
When the thermostat is satisfied, the relays de-energize and after a short time delay, the elements and fan shut off.
Please give Airstream Services a call for all your furnace needs: (615) 685-8822