Central HVAC systems use ductwork and mechanical blowers to deliver heating and cooling across a home’s primary living areas. Refrigerant-based systems, such as heat pumps and air conditioners, use pressurized gas that raises or lowers the temperature by absorbing heat. Their principal components include the evaporator coil, compressor, condenser coil, and blower. Furnaces generate heat by burning fuel, such as oil, propane, or natural gas. Energy from the burners is captured by a heat exchanger, and a flue exhausts combustion byproducts outdoors. Nowadays, homeowners can choose between dual-fuel systems, ductless heat pumps, and variable-speed models that provide enhanced comfort and efficiency.