Undersink tankless hot water heater?

[GH85Carrera]

Originally Posted by Zeke

What is a hot water heater? Never seen one.

My parents lived in a house built in the 1930s. The regular water heater was in the detached garage. The hot water went first to the master bathroom, then to the front 1/2 bath and then to the kitchen. When mom wanted to wash dishes or wash her hands in warm water, it was a 60 second wait at best. In the winter, it took even longer.

They installed a little cute water heater on the hot water line to have enough instant hot water for most tasks. It was fed by the hot water line, so it heated the hot water.

At the last photo lab where I worked we had three heavy duty water heaters plumbed in series. We had multiple processors that required a continuous flow of 100 degree water. In the cold dead winter, the water came into the building at 40 to 41 degrees. The first water heater would get the steady flow up to 60 the second one took that water and got it up to 90 or 100 but all the processors were running it would drop to 85 or 90. The third water heater would get it to 110 and the processors had a mix valve to add cold water to have it stay at 100. So it was heating the hot water.

In the summer we would put the first heater in vacation mode, and the second one in low heat and only the last one in normal heat. If one failed, it was fast and easy to swap just the one unit and not have to buy some enormous commercial water heater that was crazy expensive and massive.