Mark, Eric, George, and anyone else. Please consider using a tempering valve at the exit from your normal hot water heater, just prior to getting to the supply to the rest of the house.
Most domestic hot water is around 120*. any hotter and you risk getting scalded or a burn. If you use up the cooler 120* water in an average 40 gallon hot water heater, and then the 200* water gets into the supply you can have some painful consequences.
If you have kids taking showers this could be serious.
A tempering valve is not real expensive, around $50 if you shop around. and also not difficult to hook up. It adds water from the cold supply line into the hot water to control the temperature, it is manually set with a simple knob.
If I was at home I'd take a photo and post it, but I'm in Houston tonight. Maybe this weekend I'll get a photo and some links to suppliers of tempering valves.
Mark and Eric, I think you may have too much of a good thing: too much coil area for the amount of heated water you will be using. It may be necessary to hook up a length of baseboard heat or radiators to the system to drain away some BTU's.