Which component is typically absent in a mid-efficiency furnace compared to a High Efficiency gas furnace?

A mid-efficiency furnace generally lacks a secondary heat exchanger, which is a key component found in high-efficiency gas furnaces. The secondary heat exchanger plays a crucial role in extracting additional heat from the exhaust gases after they have passed through the primary heat exchanger. This process enhances the overall efficiency of the system, allowing high-efficiency furnaces to utilize more of the heat produced during combustion.

In contrast, mid-efficiency furnaces typically vent more exhaust gases without the additional heat recovery offered by the secondary heat exchanger. This means that they do not make use of all the energy available within the gas being burned, resulting in a lower annual fuel utilization efficiency (AFUE) rating compared to high-efficiency models.

The presence of a main burner, blower motor, and thermostat is standard in both mid-efficiency and high-efficiency furnaces; hence their functionalities do not differentiate between these types of systems. The absence of the secondary heat exchanger is what distinctly separates mid-efficiency furnaces from their high-efficiency counterparts.