What is the BTU released by condensing water vapor on a gas furnace with over 90% efficiency?

In a gas furnace with over 90% efficiency, particularly those that condense water vapor, the process of combustion not only heats the air but also generates significant latent heat from the water vapor in the flue gases. In this case, when the furnace operates efficiently, about 970 BTUs are released due to the condensation of water vapor.

This value represents the effective amount of heat recovered when water vapor condenses back into liquid form, contributing to the overall efficiency of the furnace. These high-efficiency furnaces are designed to utilize this latent heat — which would otherwise be lost in less efficient systems — increasing the total heat recovery from the gas combustion process.

Understanding that the efficiency rating of these systems often means they are set up to capture this latent heat is crucial. Thus, the specific number of 970 BTU delineates the effective utilization of the energy produced during the condensation process, confirming it as the correct choice in this scenario.