Heat Exchanger: I went with a PEX heat exchanger. One coil, 300 feet long, one-inch nominal size. I liked the idea of having a large volume inside the tube. However, it did have a nasty plastic smell for the first three weeks of use. I’m not convinced it is any better or worse than a shorter copper coil, it’s just what I went with (3/4”x60’ copper was the same cost). I bought Uponor brand, and as I measured the inside diameter, there is 8.6 gallons of water inside. The c