A condensate drain pump is used to transport water from a heating or cooling system, such as an air conditioner or boiler furnace, that creates condensation. Condensation in a system generally develops when it is operating in warmer water and the humidity in the air is high.
A condensate drain pump is generally not necessary in a system that is installed where gravity can be used to drain excess water. The pump becomes necessary when an air conditioning system is installed in a basement or without gravitational access to a drain pipe. As of 2015, the size of home-grade condensate drain pumps are generally around the size of a shoe box.