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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A lot don’t, if I take a “normal” shower there is no problem, if I want to take a very long shower it runs out of hot water
Maybe outside the scope of the eli5 (and potentially pedantic?) but a boiler and a water heater (which is what the OP is asking about) are different appliances.
Water heater – for potable water (drinking/bathing)
boiler – for a baseboard heating system
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Sparky here.
There is 3 main components to your water boiler.
1. A cylinder supplied with constant COLD water.
2. A heating element that heats the water
3. A thermostat that turns the element off when the water has reached the set temperature.
The thermostat will typically be set between 55-65C (you do not want BOILING water coming from your tap for safety reasons).
Take brand new installation, the water is cold, the element will switch on until the water reaches temp, the element is turned off.
Your tank is sealed and insulated and will stay hot for quite sometime, when the thermostat notices the temp has gone too low, it will kick the element back in until it reaches temp again.
When you use water, that temp will drop faster as you are introducing cold water while losing hot water.
You likely have a large tank and a water restrictor in your shower head.
Your element is able to keep the the heat up enough to combat the fresh cold input.
At my unit I have no water restrictors and a small tank. I get about 5-10minutes of hot water before the temp drops faster than the element can heat.
Fire make water go hot hot. Are you really 5?
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.
How does it work with places like hotels? Sometimes hundreds of showers with many guests using many at once? Is it multiple boilers or one huge boiler providing constant hot water? At any decent hotel you seem to never run out of hot water.
The sad thing is he has videos for a lot of common questions, but it’s “illegal” via ELI5 rules to just post a video link as a top-level answer.
You can solve the problem of your showers going cold by switching to a tankless water heater.
You got the explanation of how a boiler tank works, but also take the mixer in your shower into consideration.
The water in your boiler will usually be 60°-80°C (140°-176°F) – way to hot for a shower. So you’ll adjust the mixer to get a pleasant 30°C or 86°F. These mixers also have a bit of safety built into them so that you are unable to scold yourself.
The mixer itself has a clever little wax valve that keeps the output fairly the same even when the hot water supply slowly drops in temperature. You wouldn’t notice that the temperature in the tank dropped until the hot water drops below your set temperature.
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