The two types of heat in HVAC systems are mechanical heat and thermal heat. Mechanical heat is generated by a furnace or boiler, which uses fuel to create heat energy. This energy is then transferred to the air in the form of hot air. Thermal heat is generated by a heat pump, which uses electricity to transfer heat from one area to another. Heat pumps can be used to both heat and cool a space, making them a more efficient and cost-effective option than mechanical heat.