Hot water running out?

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So I live in northern Europe in an apartment and I’ve never had a problem or even head of people in my country having the hot water run out, so how does it do that? I guess in a house you have a water heater but doesn’t it just automatically heat up more water.

I hear this in a lot of tv shows and movies that’s now found out about this phenomenon

know it sounds stupid lol but I cant stop thinking about this

In: Technology

So it depends on your heating system. For older water heaters they basically had a tank of water that is pre heated. As it drains new water flows into it at the same rate and that is constantly heated. The issue is that it can drain faster than it is heated. In some modern heaters it doesn’t have a tank and is just heated really fast as the water passes through.

There are two ways of heating hot water for showers and such.

One system has a boiler that heats the water as it is being used. It runs through the boiler and is heated right then and there.

However in many places, instead there is a big water tank that is always kept heated. Those boilers don’t need to be as powerful as they can heat the water up slowly, but this also means that if you use a lot of hot water in one go, that tank can run out of hot water. Then you need to wait for a while until you have hot water again.

In the US, it’s common to have a water heater that has a tank to hold hot water, and the water heater isn’t actually powerful enough to heat the water as fast as you use it so if you take multiple showers back to back you can empty the tank of hot water. The water heater also serves the entire home (so two people can often take a shower at the same time and use up the hot water in the tank).

My understanding is in many places in Europe, you instead have an electric hot water heater for every spot that needs it (such as the shower), and not one central hot water heater.

American homes typically have tank water heaters, that [look like this](https://www.homedepot.com/p/Rheem-Performance-50-Gal-Tall-6-Year-38-000-BTU-Natural-Gas-Tank-Water-Heater-XG50T06EC38U1/205811151). They will typically have a capacity of approx. 50 gallons (so I guess about 200 liters).

So if you had multiple people showering in the home at the same time or somebody showering while another’s washing dishes, etc. you might experience enough hot water use that the tank can’t replenish as quickly as it’s being used.

Was probably more of an issue in the past when there were larger families, say when baby boomers were growing up and families often had 4+ kids. With smaller households in general now, it’s less of an issue.

A water heater is typically just a large tank filled with water, that has some kind of heat source embedded in it.

When you take a shower, some perfectly normal, fresh, cold water is added to the tank. And that cold water will, of course, chill down the hot water depot. So the second that happens, the heater turns on in the tank.

The heater is, however, not powerful enough to keep up with the water consumption of a shower. Which is why you need the “head start” of a already filled and preheated tank full of hot water; take a long enough shower, and the tank will eventually be filled with nothing but cold water. And that’ll be what you get in the shower as well. Cold water. Because you’ve ran out of hot water.

A few hours later, the tank is heated up to its intended temperature again. And you can again take a hot shower.

The trick is 100% about installing a hot water boiler with a tank that is large enough that it holds enough hot water to absolutely and certainly not run out with typical household use.

I’m my house, that number is two hours. Two hours showering, and I get nothing but cold water. Good thing it never happens with typical use…