Stealing Heat to Warm your Water

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I just read one of the most amazingly radical ideas I have seen in a long time.

One thing we use a lot of is warm water.  Compared to heating the house, of course, it doesn't cost a lot, but taken by itself, the energy for water heating is quite significant.

On the other hand, in many states --most states south of the snow line-- roads and sidewalks get very hot in warmer weather.  The idea is this: pipe cold water through these sidewalks and similar places (e.g. parking lots) in the summer: cheap hot water.  As an additional incentive, the sidewalks and parking lots are kept a little cooler (or a lot cooler, depending how the water is piped), improving the temperatures outside living areas, and lengthening the life of the sidewalk/parking lot.

A similar idea is to use passive solar heating, but that is --when you think about it-- a very individualistic idea: you invest in passive solar heating to benefit you and your family solely.  This sidewalk idea is more of a community thing: an entire block can benefit from it, or an entire apartment complex.

A sort of hybrid idea is to put water pipes just under the roofs of apartment buildings.  This is simply passive solar heating without special equipment.  The roof heats the water, the water cools the roof (and the building), sweet!