Another option would be to use a tankless water heater such as this http://www.homedepot.ca/product/rheem-ecosense-tankless-water-heater/902393
They come in electric or propane versions , use in a closed loop system with a small circulating pump.
Just buy one and plumb it in , simple
That was exactly my first thought but I figured I don't have the expertise to know if it's a good idea. Could that have a PID wired in to control the circulating pump?