Ok I have a interesting question for someone to help me think out side of the box. I am still doing my research on indirect water heaters. It really sounds like I have a choice of going with a 80 gallon at a normal temp. Or I could go with a smaller one and turn the temp up to 150 160 degrees and use a mixing valve. All this would be very simple until I factor in my recirculating line. If I am not drawing hot water there can't be any cold water being mixed in there with it. I suppose a person could run the cold side of the return into the cold side of the mixing valve. That would only help to a point. I have a feeling I will have to go with the 80 gallon. I am just enjoying the academic excerise. Don't get me wrong if there is a viable option that I could come up with I would love to save the cost,weight,price.