Why does hot water seem to run slower from the tap than cold water? Something to do with molecules?

Wow, I was just planning to ask that very same question. I’ve always noticed it. Especially when you turn the hot water on, and once the hot water actually makes it to the tap it slows down.


Maybe your hot water pipe is blocked. Water molecules ain’t the problem here.

No, it’s something to do with your water heater; it delivers (hot) water at lower pressure than the house line delivers cold water.

It would help if you can give some more details like type of heater etc. Gas on-demand heaters cause a substantial pressure drop which they use to open the gas valve. Not knowing what heater you have or anything else I have no idea what the cause may be except to say it is probably related to the laws of physics, fluid dynamics and “that time of the month” (to repeat a joke I made in another thread and which sank like a stone).

If you have old plumbing, this CecilLink[sup]TM[/sup] might explain it:Why does the hot water slow to a trickle after initially blasting out?

More details on query: I have electric water heater that is about 30 feet from sink. Sink has single lever faucet. It takes a few seconds for hot water to come from faucet due to distance from tank. when I first turn it on, cold water comes out fast, when it starts getting hot, flow slows down. Could be the washer theory, as this type faucet has very small o-rings and not washers.