Hello, as far as what I would do different is a tough answer because I do not know is the outcome would be desirable or not. My recommendation to someone would be to build it like I did. We had 117 degree water in the tempering tank this morning. This gives my "normal" furnace little work to do to top off the temperature.
Would I do it again? Absolutely. Especially with the cost of oil. I am looking into switching out my oil fired boiler and going with natural gas for the 2013 heating season. I did the calculation and for the tonnage I use (four @ $266 per) if you convert that over to what they charge per therm ($1.04) of natural gas it comes out less expensive. So we will see what rebates New Jersey will offer for 2013 for switching to natural gas.
I will always keep the coal stove and might use it to keep the basement at 72 during the winter months.
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Best of luck and post questions if needed.