Frozen pipes. ..

[philr]

I have a hard time believing that cold water boils faster than hot water. When I leave hot water in the electric kettle, even after an hour when I turn it on again, it boils almost immediately while it takes a few minutes for cold water to do the same!

 

When I was a kid, my father also told me hot water freezes faster than cold water to explain me why they used hot water to resurface the ice with a Zamboni at the arena. I didn't believe him and I told him it probably helped melting a part of the rough ice surface to do a better resurfacing... 

 

I thought about that again when I noticed that a hot water pipe I ran next to a cold water pipe would often freeze and not the cold one, but I thought that there must have been a better explanation...  I figured that the hot water pipe when unused dropped to the same temperature as the cold one since the water doesn't circulate and being just two inches away from the cold water pipe, nearer to a concrete floor and some air leak from outside was enough to make it freeze. The pipe would freeze even with a room temperature of 80°F.

That problem was quickly fixed with a can of foam insulation that did away with the small air leak!  A friend of mine has the same problem in the kitchen of his old house with "piece-on-piece" construction (I'm not sure how to say that in English, I hope you understand what I mean!). He needs to remove the lower panel on his dishwasher to let the air circulate and leave the cabinet doors open to avoid freezing. Otherwise, even the drain pipe of his KDSC-18 freezes...  He thinks the problem comes from a former kitchen remodel where they relocated the vent hood exhaust and didn't care re-insulating the hole adequately at the former location.  That makes sense but to correct that, he'd need to remove the cabinets and ceramic tiles on the wall and he's not ready for that yet... I suggested to simply cut holes in the floor under the cabinets/dishwasher as the basement is well insulated with urethane foam and he keeps it hot to have a warmer floor. He didn't bother doing that either so he just leaves the cabinet doors open and the faucet dripping...

 

[kb0nes]

Phil,

You are correct, cold water in NO way boils faster then water from a higher temperature. Yes it is true that heat flows through a thermal resistance faster if the temperature difference across that resistance is greater. But the higher temperature water has such an energy head start that any tiny thermal transfer advantage is moot. I ran a couple cycles with a recording thermocouple bringing 2 Kg of water to a boil, the 120 F water boiled in a fraction of the time the 50 F water took... Myth busted

My hunch is that freeze testing will prove out that any possible Mpemba effect is tiny and fleeting. I'm running some tests now on hot vs cold water freezing currently. I will post the results in a different thread once freezing tests are done. I'd have responded to my father in the same manner as you did regarding the Zamboni statement too.

In the case of household plumbing, with all variables normalized, I still believe there is no practical difference between the time either line would take to freeze. And given a tiny amount of flow, the hot will be less likely to freeze due to the additional heat energy the incoming water has.

If I had the issue of freezing in long lines running through an unheated crawlspace I'd install one of the hot water recirculation pumps as was posted up thread. Heat tape would work too but the recirculation system would be useful anytime as it reduces time to get hot water. Of course since it flows back through the cold line it would prevent freezing in both lines! The pump is simpler to install too as it is done under the sink, although the lines should be insulated too so I'd still have to get dirty if they weren't already insulated.