Trivial question about hot water supply

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OrionRed

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I am having trouble figuring out why, when you turn on a distant faucet, the water SLOWLY gets hot. It seems to me that it should be cold...cold...cold...hot.

It doesn't seem like the copper pipe should cool it off that much between the tank my bathroom. It's maybe 50 feet of run.

So...is the cold water in the pipe also mixing with the hot water running towards the faucet, or is the copper taking all that heat?

Like I said, it's trivial. But now that I've noticed it, I can't stop thinking about it.
 
There are two physical properties to factor. One is the thermal mass of copper and the other is the thermal conductivity of copper to the surrounding air. Copper is quite good at both. The large solder irons are made of copper because they can absorb a lot of heat. Copper is used in heat exchangers such as a heat pipe inside a computer.
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It is also the reason why hot water pipes should be insulated, to retain the heat. The copper does NOT "soak up the heat" it transfers it from the water to the surrounding air. And it occurs in direct proportion to the difference in temperature between the water and the air. The cooler the air, the longer it will take for the water to get "hot".
 
Another reason for warm water before hot is heat migration from the tank to the outlet pipe. If you touch the outlet pipe it will be warm for a couple feet.
 
quote; Another reason for warm water before hot is heat migration from the tank to the outlet pipe.

As stated previously, it is NOT another reason, it is the ONLY reason why it happens.
 
No there are 2 things going on, 1 is the heat loss while the tap is open and running through the copper, the other (what I'm talking about) is the migration of hot water into the outlet pipe while there is no water being used. This will cause warm before hot as well.
 
So the water in the tank circulates a little bit up into the outlet pipe? Is it actually moving some water with convection, or is it the copper conducting heat out of the tank? Or both?
 
Convection is moving the heat out of the tank, but that is merely accelerating the movement of the hot water to the faucet when it is opened. The convection ONLY occurs in the piping that is rising from the heater. As soon as the piping turns downward the convection stops.
 
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