High efficiency gas furnaces may use ______ pumps.

• A. condensate
• B. circulating
• C. fuel
• D. air

Answer: (A)

High efficiency gas furnaces produce liquid condensate from the combustion gases as they cool in a secondary heat exchanger. That condensate collects in a trap and must be moved away to prevent overflow and corrosion, so a condensate pump is used to lift and discharge the water to a proper drain. This pumping is a direct result of the condensing design, which differentiates high-efficiency units from older non-condensing models. Other pumps mentioned don’t fit this setup: circulating pumps are for circulating hot water in radiant or hydronic systems, fuel pumps aren’t part of typical natural gas furnaces, and air pumps aren’t used for handling combustion condensate.