-=> Quoting Floyd Williams to Tim Hutzler <=-
TH> I need more information on the last part of your question. If you
  > paint your tanks ultra-black, and you don't live higher than
  > 60-deg lat, then you can expect about 100W/per sq/ft. input.
FW> Is this Watts/sqft/time??
You can take it either way. The heat input is about 100W. Over the
period of one hour it would be 100W/hr.
FW> Mobile, Alabama near the Gulf of Mexico. I will look the latitude
  > up on a chart.
 
No need to - you have plenty of sun energy units there - even on the
coastline.
TH> I used three water heater tanks in a 5x8 box - that's 40 sq/ft...
 
TH> Right now in the afternoons the water too much too hot to touch.
  > That's when we run the dishwasher. Those who adjust their
  > lifestyle ! Origin: Madman BBS * Chico, California * 916-893-8079
  > * (1:119/88)
FW> What do you think of this idea as a comprise: I have noticed that
  > we seldom use more than about 10 gallon of hot water at any one
  > time.
But how often do you draw from this 10-gallon increment?
FW> Since I have had little luck in finding a discarded water heater,
Suggestion, post a message in a few of the plumbers stores and pass
the word around. Offer free pickup. They *will* call. However make
sure you find out why the tanks are being discarded. If the thermostat
went out, it's a good candidate. If they are replacing a electric
unit, and it's not too old, that's another good candidate.
Watch out for old, leaking units. Avoid the galvanized talks, they are
crap. The glass lined tanks usually only leak around the fittings, and
that is easily repaired. Figure on two out of three. The bad ones
still make a nice smoker. 
Cut the ends off and you have a culvert. 
FW> I'm thinking of just placing two lengths of 2 1/2" black plastic
  > pipe on the roof just above the hot water heater. This would
  > store about 10 gallon and discharge directly into the existing
  > gas fired hot water heater. Black pipe laying on a black roof
  > would absorb the heat. If I placed the pipe in a box, the box
  > would be about 2 x 21 feet. Area of the pipe exposed itself is a
  > little less than 9 ft2. Is this idea creditable?
Plastic is a poor conductor of heat, but it is cheaper than copper. I
think it will work fine in your area. You don't get too many freezing
nights, do you? Also note that in the winter you will loose heat,
lowering the street water temp, which your waterheater has to
overcome.
FW> I think the pipe would look better that the box?
I take it that the front of your house faces mostly south?
FW> How much heating capability would I loose by not putting the pipe
  > in a box?
Quite a lot. Convection currents and wind are real heat robbers.
best regards,
Tim
 
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