Thanks.
In fact, over the weekend, I found two almost turn-key solutions.
This UK one almost out of the box:
http://www.stokvisboilers.com/HeatPlateExchangers.asp
And this Dutch one (also available with Alfa Laval) needs a little more work of putting together the items but both solutions are made specifically made to use hot cooling water to heat up tap water.
http://www.itho.nl/Pages/Itho.aspx?F...5E02/8549.aspx
Thorwald