Part of the reason that I ultimately decided against a HW loop was the potential to cook the tank. Runaway heating is a very common cause of tank crashes. I've built redundancy into my current heating approach with multiple heaters and dual controllers, but the HW loop would have been much less secure. Since the amount of heat from my HW heaters is essentially infinite, a major failure of the control mechanisms would quickly spiral things out of control. OK, I get that there are folks that have done this without any problems but I just felt the benefits did not sufficiently outweigh the drawbacks. Also, when I converted my system from a 12mm glass tank to a 1 inch acrylic tank, heat wattage required dropped singificantly.