Question 199General Subjects - 1st Asst/Chief

The correct answer is A) The introduction of air via the makeup water. The primary source of air contamination in a properly filled hydronic heating system is the makeup water that is added to the system. When makeup water is introduced, it often contains dissolved air that can come out of solution and cause air pockets or air bubbles within the piping system. This can lead to reduced heat transfer efficiency and potential system damage. The other options, such as air from the expansion tank vent, convector steam supply, or atmospheric drains tank vent, are not the primary sources of air contamination in a properly filled hydronic heating system.