Final answer:
The three types of furnaces in the HVAC industry are gas, electric, and oil.
Step-by-step explanation:
The three types of furnaces in the HVAC industry are gas, electric, and oil.
Gas furnaces burn a fossil fuel, such as natural gas, to provide direct heat for space heating, water heating, and cooking.
Electric furnaces use electrical current to generate heat by running it through a coil of wire that glows orange.
Oil furnaces burn oil for direct heat, commonly used in areas where gas or electricity may not be readily available.