How a Furnace Works

How does a furnace actually work, and what is all that whirring and clicking that happens before any heat comes out of the vents? This video opens up the box in your basement and walks through the whole machine in plain language, in the exact order things happen when you turn up the thermostat. The simple version is that a furnace only does two things. It makes heat and it moves heat, and every part inside is there to do one of those two jobs. We follow the full sequence from the moment the thermostat calls for heat: the draft inducer fan that clears the vent first, the pressure switch that proves the airflow, the hot surface igniter, the gas valve and burners, and the flame sensor that confirms the fire actually lit. Then the blower kicks on and pushes warm air through the house. You will finally understand the heat exchanger, why the fan keeps running after the heat shuts off, and what the difference is between a single-stage, two-stage, and modulating furnace. We cover electric furnaces too, plus AFUE efficiency, why high-efficiency units drip water, and the carbon monoxide safety you should know. None of this is complicated once you see it laid out. Sources: HVAC.com - How Does a Gas Furnace Work, and What Is an Electric Furnace. PICKHVAC - Gas Furnace Sequence of Operations and how a gas furnace works. The Furnace Outlet - Single-Stage vs. Two-Stage vs. Variable Speed, and heat exchanger crack symptoms. Structure Tech - Heat Exchanger Cracks and Carbon Monoxide.