Yesterday, I was at a home where the seller was boasting about his hot water tank replacement that he did himself. There were no inspection stickers on the tank, so I gather there was no permit pulled. He installed a expansion tank on the hot water pipe about a foot up from the tank. Now with a hydronic heat conveying medium, the expansion tank will obtain the extra water created when the water is heated and it expands. The diafram divider in the tank can also help increase water pressure in the system which I have read in the HVAC course here on Nachi. But what about the water tank?? Does this expansion tank help, hurt or no change in the system??. Your thoughts, Thanks Rick
The diafram type does not help increase the pressure. The closed steel tank does. I stand corrected.
Closed Steel Tanks
The closed steel tank has no diaphragm and no moving parts. It is simply filled with water (about two-thirds) and air (about one-third). When the boiler heats up the water, the water expands and enters the tank. As the water enters the tank, the air inside the tank gets compressed. The compression of the air inside the tank results in an increase of system pressure. That pressure can be measured at the pressure gauge of the boiler.