My family is building a small house in central MN on a property with a 30 gallon/minute Artesian well at 47 °F. These calculations, if correct, show that there should be more than enough thermal availability in the well water to supply a 1.5 - 2 Ton heat pump. I am trying to size the heat exchanger for the Artesian well. Proposal for HEAT EXCHANGER: 3 Ton spiral-coil Turbotec heat exchanger, 36 kBTU/hr 0.833" ID outer spring water pipe. 0.625" ID Copper, twisted heat pump fluid pipe inside outer pipe. OR possibly a 1.125 ID outer pipe and 0.875 ID Inner pipe for less flow restriction. Model Number Nominal Size A B C D E F G H J K L M Unit Weight C-5984-01 36K 0.883 0.883 0.625 0.625 14.00 15.75 5.19 10.88 2.50 2.50 4.44 4.00 26.00 lbs. OR C-5924-01 60K 1.125 1.125 0.875 0.875 17.25 18.00 7.63 14.00 2.50 2.50 6.75 5.38 56.00 lbs. turbotecproducts d@t com /products/spiral-coils ======================================= OPERATIONAL SCENARIO: Water Temperatures on coldest Winter night with 47 °F Artesian spring water temperature. 30 °F Cold pipe at house, cooled by heat pump 31 °F Cold pipe at Artesian Well 42 °F Hot pipe at Artesian Well, 11 °F temperature rise with 16 °F differential. 41 °F Hot pipe at house; 11 °F temperature differential for heat pump to work with. For each Gallon/min flow rate and 1 °F temperature, there are 147W of available thermal energy. At 1/4 spring flow rate, 30/4= 7.5 GPM -> 1104 W per °F 2.5 kW would need 2500/1104 = 2.26 °F (2.5 kW is calculated actual heat load, < 1 Ton) Given the heat exchanger Diameter "E" of 15.75, 3 full revs (from drawing), count the 4 smaller, inner revs as 2 outer -> 5, 15" revs. 5 * PI * 15 = 235" = 19.6' heat exchanger linear length. The Volume of spring water in the heat exchanger would be the differences in the circular areas of the outer and inner tubes times the length. I estimate 0.311 gallons. At 7 gal/min -> 2.67 seconds trip time from A to B through exchanger. The inner tube is twisted to create turbulence and increase surface area of heat transfer. (5.42 seconds running the Artesian water through the inner, 0.875" with the larger heat exchanger) With almost 20 linear feet of contact length and 2.67 seconds contact time and 47 °F spring water contacting 31 °F antifreeze for 16 °F temperature difference, 2.26 °F final temperature rise should be quite easily done. I am not sure at which temperature difference Turbotech sizes its devices. Is this analysis reasonable?