Wood fired domestic hot water heater

I made this wood fired water heater from a used 40-gallon natural gas fired Rheem water heater. I just removed the gas burner and then added a firebrick-and-perlite-refractory-lined firebox to the bottom. The firing door is just a $10 Vogelzang chimney cleanout door. The grates are welded together from 5/8" concrete rebar. It makes lots of hot water with very little firewood. Yes, I know the term "hot water heater" is redundant. Find other fun projects on http://www.dansworkshop.com

Update: December 29, 2012 - The water heater is still in great working condition, I estimate that it has saved me over $300 already in water heating costs (teenagers in the house) in the three and a half months of use.

Update: December 31, 2020 - The water heater is still working great! I have to patch the fire brick every so often, and also rebuild the grates once a year (which only costs about $5).