Underroof copper pipe water heating

[ashdown]

In an effort to cut water heating enegy costs do yoou think it would help significantly to run perhaps a hundred yards of copper piping directly under my south facing roof so that I could feed slightly heated water into my roof-mounted hot water cylinder?

[master plumber mark]

for alll the trouble , probably not...especially if you are only trying to heat your water.

even the solar systems people put in sometimes never re-coupe the original investment.


theres lots of PASSIVE things that can work for a heating exchange by just moving hot air alone on the south side of your home through air type solar panels.... if you want ot heat your house in the winter.

[jimbo]

You didn't explain much about this "roof mounted cylinder". True that if the attic is hot, then standing water in the pipes would warm up. But if there is any flow at all, the temp rise would be minimal. It seems to boil down to this: you would save the cost of heating the volume of water in that pipe loop ONCE per day. Not much savings here. There is a bi difference between a loop of pipe in a warm attic, and a true solar collector.

[hj]

Plain pipe is notorious for not absorbing many therms, except when the water is stationary. Once the water begins to flow, you can calculate how much water was stored in the pipe, and that is the amount of hot water you will inject into the tank. Now if the pipe had "radiator" fins on it and was painted black like in a solar collector it would absorb more heat, but probably would not save as much as the pipe would cost. A true solar collector on the roof next to the heater would probably cost very little more plus the controls and would do a much better job.