Honeywell expansion tanks are responsible for absorbing hot water within closed heating systems. With the help of butyl diaphragms, they separate the air from the system water. When pre-pressurized, the tank maintains minimum pressure to allow fluids to circulate. Honeywell recommends installing their expansion tanks by screwing them into the 1/2 in. connection on the bottom of a Honeywell Air Eliminator or air purger. Shop Honeywell Expansion Tanks and other great products right here at Jackson Systems & Supply.