4 ms·
I was just thinking about this earlier today when washing my hands in the sink. When you first turn on the hot water tap in most homes, the water that comes ou
by schoen 10mo ago
I was just thinking about this earlier today when washing my hands in the sink.
When you first turn on the hot water tap in most homes, the water that comes out is cold. After some period of time, hotter water starts to come out. My mom used to describe this as "waiting for the water to warm up".
For decades, I didn't consider the mechanism behind this. That is that there is water in the pipes between the home water heater and the tap. That water can't retain its heat without any further heat input, and gradually loses heat and comes into near-equilibrium with the temperature of the rest of the house. The hot water inside the water heater tank, on the other hand, is constantly being reheated as necessary by a heating element.
When you turn on the tap, after not having used it for some time, you're waiting for cold water from the pipes to be flushed out through the tap and be replaced with freshly heated water from the tank. Once this happens, the water coming out of the tap will be hot because it's been heated recently enough.
I probably didn't realize this until I was about 30 years old, and then I thought of Feynman's anecdote of his students not connecting their theoretical knowledge to understand the mechanism of a real physical situation. It seems I wasn't curious enough as a child to apply my own knowledge to the mechanism of the hot water tap!
- rramadass 10mo agoOne of the best ways to learn to think Scientifically i.e. in terms of Physics/Chemistry/Mathematics/Biology is to start with the classic Soviet era books by Yakov Perelman - https://mirtitles.org/?s=yakov+perelman https://mirtitles.org/?s=yakov+perelman Specifically; start with the 2-vol Physics for Entertainment (the breadth of coverage is really good) followed by Mathematics can be Fun, Algebra can be Fun etc. Note: Do not be misled by the words "Entertainment"/"Fun" etc. in the title. As is typical of Soviet era books these are serious works with precise, succinct and focused topics quite unlike most current "pop science" books.
- anovikov 10mo agoWeirdly enough, this is not the case in the former Soviet Union. Because there's always a reverse pipe ("obratka") that has hot water constantly circulate and the only part that cools down is the small portion of pipe between "obratka" connection and the faucet, so "heating up" takes a second tops. It's puzzling why no one in the civilised world adopted this idea :/ Many things are told about emigres being constantly homesick etc., and i believe this is largely bullshit, but this is the only thing i really miss from my Soviet past.
- wingspar 10mo agoIt’s a thing in the US too, but not common. I always understood them to be expensive to use, as you always have a pump running and hot water cooling down and needing reheating. Hot water recirculating pump. https://www.familyhandyman.com/article/hot-water-recirculating-pump/ https://www.familyhandyman.com/article/hot-water-recirculati...
- anovikov 10mo agoYes, in the Soviet Union, hot water was a byproduct of production of electricity - using combined heat and power, it was a waste heat. And it used lots of electricity to make weapons to advance dictatorship of proletariat, so there was plenty of free heat, too.
- jasonpeacock 10mo agoMy house originally had a recirculating pump for the hot water but it burned out. Somehow though, it still (mostly) worked and had instant _warm_ water. I think it was through natural convection/circulation - the hot water expanded in the tank and pushed it through the recirculating loop? So maybe there's a good-enough solution that doesn't require a pump, just a return loop. Now I have an on-demand water heater with a built-in recirculating pump, so it's instantly hot :)
- 0xfaded 10mo agoThis is how rooftop solar water heaters circulate water as well. Though these days you'd be better off with PEV plus a small electric heater.
- mixmastamyk 10mo agoYou can install an immediate hot water heater at the sink if you’d like.
- Tyrannosaur 10mo agoHot water recirculation is a thing I have heard of done in the United States. I don't know how common it is, but a simple Home Depot search brought up a bunch of results for options. https://www.plumbingsupply.com/recirculating-systems-explained.html https://www.plumbingsupply.com/recirculating-systems-explain... https://www.homedepot.com/s/hot%20recirculation?NCNI-5 https://www.homedepot.com/s/hot%20recirculation?NCNI-5
- cwmoore 10mo agoSame with cold water.
- schoen 10mo agoI don't think I have anything in my house (other than an ice cube tray?) that's meant to deliberately make cold water colder than the ambient temperature of the house! Maybe some people do, though, especially in hotter parts of the world.
- yetihehe 10mo agoWater in mains pipe is typically colder than your house walls (where the pipes go). So you need to flush some water from your pipes to get that colder mains water.
- schoen 10mo agoThis is a good point I think is comparatively less noticeable where I live. But on reflection, I've sometimes noticed it.