What are the two main types of gas furnaces?

The identification of the two main types of gas furnaces as conventional and condensing is based on their design and operational efficiency. Conventional gas furnaces utilize a straightforward design to burn natural gas or propane to heat air, venting combustion gases directly outside. They typically have a lower efficiency rating, often around 80% or less, as they lose much of the heat generated through the flue gases.

Condensing gas furnaces, on the other hand, are engineered to maximize efficiency. They extract additional heat from the exhaust gases, which causes the water vapor in the combustion gases to condense. This process allows condensing furnaces to achieve efficiency ratings of 90% or higher. By capturing and reusing more heat, condensing furnaces can provide significant energy savings and decreased greenhouse gas emissions, making them the preferred choice for environmentally-conscious consumers.

The other options, while they address different categories and characteristics of furnaces, do not accurately reflect the primary types of gas furnaces in terms of their design and efficiency focused on gas burning technology.