Wow! Quirt, your house is such a unique situation. I think it’s safe to assume that you’ll get a great ROI, esp. if you include comfort and convenience in the definition of “return.”

Dual speed fans for both. It saves a lot of energy. What typically happened was the higher speed fan brought everything to the right temperature quickly, then the lower speed fan kept it there. I think it was supposed to extend the life of the air handler since it wasn't constantly turning on and off.

Ahh good to know! Thanks!