How a Gas Furnace Works

For most Twin Cities homeowners, the forced-air heating and air conditioning system in their homes is something of a mystery. Today’s high-efficiency gas furnaces operate reliably and quietly, usually in the basement, and get noticed only when they aren’t working properly. The homeowner sets the desired temperature on their thermostat and that’s it, except for changing the filter occasionally. The house stays comfortable and the central heating and cooling system often can’t even be heard in well-insulated homes. As a leading residential heating service company in Minneapolis and St. Paul, we believe that understanding more about this equipment can be very useful, so we’re glad to provide this brief guide to explain how your gas furnace works. Here’s a step-by-step description of the basic operation sequence:

• The thermostat controls the process – The thermostat in your home is little more than a temperature-controlled switch. It may be a simple device or a programmable unit that gives you unmatched control of your home’s comfort system. Operating on a low voltage supplied by the furnace, it monitors the temperature in your living area. For heating, when the temperature drops below the level you set, the thermostat sends a signal to the control board in your furnace, telling it to start heating. When the temperature reaches the desired setting, the thermostat sends a “turn off” signal.
• The controller starts the ignition sequence – When the start-up signal comes from the thermostat, the digital control board starts the process to begin heating your home. The sequence is:
  • The draft inducer fan starts – This fan blows air through the combustion area and exhaust vent. Once the draft is established, a sensor confirms that the combustion airflow is correct and sends an OK signal to the controller.
  • The gas valve opens – With confirmation that correct combustion airflow is established, the controller opens the gas valve, allowing natural gas to flow into the burners.
  • The ignition sequence begins – The ignitor, either a spark or heated surface ignitor, lights the gas flame.
  • Ignition is verified – A sensor indicates that the gas flame is burning by detecting the heat.
  • Safety tests – If any of the steps in the sequence fails to occur correctly, the controller shuts off the gas flow and terminates the ignition sequence.
• The main blower circulates warm air – Once the burners are lit, a timer or temperature measurement signals the controller board to start the main blower after a short delay. This prevents cold air from being sent though the air ducts. After passing through the air filter, cooler air from the return ducts flows over the heat exchanger, where it is heated. The warm air then circulates through the home through the air duct system and registers.
• After the desired temperature is reached, the furnace shuts down – When the temperature in the home reaches the desired level, the thermostat sends a “shut off” signal. The controller board closes the gas valve and extinguishes the flame. The main blower continues to run for a set time or until the heat exchanger has cooled, and then it stops.

Designed for Safe Operation

The controller board monitors every operation of a gas furnace. Any time an error is detected, the system shuts down for safety reasons. Depending on the brand and model, the nature of the error may be stored as an error code by the circuit board and can be recovered by a technician. In other models, the technician uses a manual diagnostic process to determine the cause of ignition failure. For the homeowner, though, most problems will be noticed when the furnace stops heating the home. That’s when to call a reliable, trusted HVAC contractor like our award-winning company.

Expert Gas Furnace Diagnosis and Repair Services – Minneapolis St. Paul, MN

Only fully trained, experienced technicians should handle home-heating problems. Handymen and homeowners should never attempt to repair any gas furnace, for obvious safety reasons. As a leading home heating and cooling contractor in the Twin Cities, our team of highly trained, certified HVAC technicians has the long experience needed to handle any problem with your heating system, regardless of brand. When you call us, we’ll respond quickly, diagnose the problem, and give you an accurate, competitive cost estimate for the repair. With your approval, we’ll fix the problem efficiently and correctly. For many repairs, any needed parts are already in our service van. Restoring your heating quickly is our priority. Call us anytime, even on weekends or at night.