How is the pressure maintained in hot water coming out of the heater? Obviously, when cold water runs into the heater, its pressure is dissipated in the empty area above the water level, around the sacrificial anode…but how is the pressure restored when hot water issues from the tank?
It’s a sealed unit. So the pressure is alway the same.The cols water inlet lets the cold water out at the bottom of the tank , And the hot water outlet pipe is near the top.So when you turn on the hot water , cold water is let in at the same time.
Oh, OK. Thanks. 
Be sure to install a pressure relief tank into the system , if you ever have to install a one way valve at the water source to prevent backflow. The tank will contain the expanded water when heated. Without the tank the weakest link will fail as the pressure increases, be it the water heater, a pipe, or faucet, something will leak.
Unbelievably, I’m on my third hot water heater in eight years. Damnation, they don’t make 'em like they used to. At any rate, every one I’ve had pass through here has had a built-in Blow Valve. In the somewhat tragic event that the thermostat gives out, and the heater won’t STOP boiling the water, the blow valve will let out the pressure. They are typically located on the wall of the heater, but up high very close to the top of the unit. Make sure yours WORKS- the manuals all had a small test you could do to insure this.
Nothing worse than coming home at 1:30a.m. after a long hard day, to find superheated water shooting up into the ceiling of your mud room at high pressure from a bad solder seam…all because the blow valve failed. Water raining down on lights, the floor, the hallway…etc. On a hot water heater that had been installed THAT DAY. :mad:
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