What type of furnace employs a secondary heat exchanger for added efficiency?

The type of furnace that employs a secondary heat exchanger for added efficiency is the condensing type. This design utilizes a secondary heat exchanger to capture additional heat from the combustion gases that would otherwise be vented outside. In a condensing furnace, as the hot exhaust gases pass through the secondary heat exchanger, they cool down, allowing moisture in the gas to condense into water. This process not only maximizes the heat extracted from the fuel but also improves the overall thermal efficiency of the furnace, often exceeding 90%.

In contrast to condensing furnaces, standard and low-efficiency furnaces do not use secondary heat exchangers and typically vent higher-temperature gases, resulting in lower overall efficiency. High-efficiency convective models may still lack the specific condensation process that characterizes true condensing types. Therefore, the design features of a condensing furnace uniquely position it for optimal efficiency in heat recovery.