GAS FURNACE OPERATION AND DIAGRAM BASICS - thermix GAS FURNACE OPERATION AND DIAGRAM BASICS. How Gas Furnace Operation Works? The gas furnace is the simplest to operate and understand. Therefore, we will use it here to look at a typical heating system. This type of natural-gas furnace is used to heat millions of homes in the United States. How a Gas Furnace Works - hometips Mar 08, 2018Gas Furnace Diagram. This illustrated guide diagrams the various parts of a gas furnace and explains how they all work together. Need Help NOW? Get a Local Heating Pro Fast! A gas forced-air heating system goes into action when the thermostat tells it that the room temperature has dropped below a preset comfort level.