Is it true hot water pipes can freeze before cold water pipes if no water is drawn from either...?

The water heater is fed directly from the cold water line, so both systems recieve equal water pressure. As far as the hot water line reaching the same temperature as the cold water line, yes, depending on the insulation, the hot water pipe, if no water is drawn through it, will eventually reach ambient temperature. The local radio station has been advising people to leave their cupboard doors open to allow heat to get to the wall where the pipes are, but I am kind of taking this with a grain of salt. It is true that any little bit helps, but if cabinet doors were good insulation, we would be lining our walls with them. as far as one pipe freezing before the other, I would almost think that if a person is going to put pipe insulation on only ONE pipe, they would put it on the hot line and not the cold line, which would give it more freezing protection. I would think that with a new, well insulated house, in weather that is not unusually cold for the region, there would not be a great deal of danger, though you say that you are letting the interior temperature stay cooler than is usual for an inhabited house; and that invites the possibility of a freeze-up. sounds like you may be away from the house? I'd suggest if you have an emergency contact, you think about having them boost the temperature a bit, and run some water from each tap, just to check for a frozen pipe.

I remember studying this a bit in a chemistry class in college. It's definitely true that hot water can sometimes freeze faster than cold water but it's not always the case. It depends on the environment, the difference in initial temperatures, etc. My chemistry teacher explained it in terms of acceleration. Picture a drag race with the cold water starting halfway to the finish line in a yugo but the hot water at the starting line in a sports car. The hot water has further to go but because of the greater difference in temperature it changes faster(accleration) so there's a chance it can pass the cold water before the finish (freezing). This phenomenon is known as the Mpemba effect. There's a very, very thorough explanation of the Mpemba effect at this site.

read the following at the address below: http://www.xs4all.nl/~johanw/PhysFAQ/General/hot_water.html

The hot water pipe will fall to the same temperature as the cold water pipe if left long enough but neither will freeze in the air surrounding them is above freezing point. The cold water pipe may freeze quicker since some of it is outdoors. Water under pressure boils at a higher temperature than water under a low pressure and so I would guess that the cold water will freeze at a higher temperature than that at a low pressure. I hope this helps but I am applying logic and do not have any hard facts to substantiate this.

I don't know the reason why be I have personal experience that tells me that a hot water pipe will freeze before a cold water pipe even it they are side by side. I suspect it is because the hot water contains less dissolved air as a result of having been heated. I have not facts to support any of this other than my personal experience.