I built one of those rocket waterheaters. It works exceptionally well I do say. I used the pass through technique using 50 feet of 1/2" copper tubing running through a 40 gallon stainless steel kettle. There is no pressure to it. It has an over flow hose going to the outside. The core is a 30 gallon barrel turned on its side with 6" pipe holding the form and I have a clay perlite mixture filling the space. I insulated the outside of the whole thing with rockwool. Anyway here's some pictures.
He loves you so much! And I'm baking the cake! I'm going to put this tiny ad in the cake:
Composting Chickens Comic (e)Book - The Ulitmate Guide to Compsting with Chickens - Digital Download