Which type of furnace produces the most condensate?

The correct answer is the condensing gas furnace, as this type is designed to maximize energy efficiency by extracting heat from the combustion gases that would otherwise be vented outside. In a condensing gas furnace, the flue gases are cooled to the point where water vapor condenses into liquid water, creating condensate. This process occurs because the unit is able to operate at lower temperatures by using a secondary heat exchanger to extract additional heat from the exhaust gases.

As a result, the colder exhaust leads to more moisture in the flue gases, resulting in an increased amount of condensate being produced. This is a key feature of condensing furnaces that not only enhances their efficiency but also plays a part in supporting environmentally friendly practices by minimizing energy waste.

In contrast, conventional gas furnaces, modulating gas furnaces, and oil-fired furnaces typically do not operate at the lower temperatures that produce significant condensation, thereby generating less or no condensate.