Expansion tanks are essential for managing pressure in plumbing and heating systems by absorbing thermal expansion using a sealed air bladder. In this how-to, Eric explains how to pre-charge and install these tanks, emphasizing pressure matching for optimal function. He compares potable and hydronic models, shows off his favorite inflator tool for setting psi, and cautions against under pressurization. Oversizing is safe and even encouraged if you're unsure. Throughout, Eric provides practical installation tips and stresses the importance of proper setup for system longevity.