A condensing warm air furnace has?

A condensing warm air furnace is designed to maximize efficiency by utilizing two heat exchangers. The first heat exchanger is responsible for transferring heat from the combustion gases to the air being circulated through the system. The significant aspect of a condensing furnace is the second heat exchanger, where the remaining heat from the flue gases is extracted while also condensing the water vapor present in those gases.

This process not only improves the overall thermal efficiency of the furnace but also allows for the capture of latent heat, which would otherwise be lost in non-condensing systems. The dual heat exchanger design plays a crucial role in achieving higher efficiency ratings, often exceeding 90% annual fuel utilization efficiency (AFUE), making these systems more environmentally friendly and cost-effective in terms of fuel usage over time.

In contrast, options indicating fewer or more than two heat exchangers do not align with the conventional design of condensing warm air furnaces.