I am in the process of building a 3600 Sq ft. Home (not including ext. Walls.) The hvac system called for a 3 ton and a 2 ton unit. My installer is recommending miami heat pump for the equipment. I sent the manuel j to them and they are recommending steping up the two units 1/2 ton each. If I do so I would need to redo the duct sizes to accommodate more air flow. I am building with efficiency in mind with the radiant barriers and high r value insulation. I think I am going to start from scratch and have a new Manuel j done from a different company and compare the two. Any suggestions on this? While checking into this I found a lot of installers use the marathon water heater with the desuperheater. I am planning on two 50 gal tanks on each unit. This may be a stupid question but why install a desuperheater with a second circulation pump when one could pipe the hot water output to the closed loop, to the heat exchange in the two tanks with a temperature control valve that would bypass the tanks when they come to a preset temperature. This is assuming that the Geo ports in the tank are a heat exchange (I don't know for sure). In fact, it seems like one could hook the same hot water loop side to the drain of an ordinary water heater and then t off the top to the loop field. Of course have temp. Bypass valves. All in all instead of having two or three water systems, there could be one. Suggestions and opinions will be greatly appreciated.