Nearly all closed-loop hydronic heating and cooling systems are supposed to be filled with water or a mixture of water and antifreeze. The only intentional air in the system is that contained in the expansion tank.

Water is the life-blood of hydronic systems. Just as we strive to maintain the health of our own circulatory systems, it’s important to maintain the health of the water-based solutions that circulate through the hydronic systems we construct and maintain.