I take long hot showers after bike rides, so I’m used to the feeling of the water going cold in a shower. What’s interesting to me is that this happens fairly quickly, seemingly toward the end of the supply of water that was hot when you began showering.
But i’ve been thinking about boilers and it’s not clear to me how this works. It occurred to me that maybe the tank only begins refilling with cool water from the pipes once it runs low — but the tanks in most places I have lived are in the basement and don’t have obvious pumps attached. If the tank weren’t full I don’t think you’d be able to maintain constant water pressure upstairs. At the same time, the hot water seems to stay hot for 30+ minutes, even as the tank is presumably refilling itself with cold city water. How does this work? Thanks!
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What a lot of people haven’t mentioned here is the mixing valve.
A vast amount of hot water heaters store water significantly warmer than you would/should ever use at the tap. So the hot water leaving the boiler gets cooled down with cold water before getting to your faucet.
This increases the length of time you receive hot water before it’s too cold to use.
As an extremely basic example, let’s say you have 100 gallons of hot water. You use the 100 gallons up and that’s it, you have to wait for the water to heat up again before you can take another warm shower.
But if the mixing valve introduces 25% cool water before it reaches you (again, just to bring it down to a reasonable temperature that won’t scald you), now you effectively have 133.33 gallons of hot water before it’s empty.
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