Most will tell you that heat kills membranes. That has not been my experience. Mine is in a garage as well, in Phoenix where it gets plenty hot, over 110 in the summer. The incoming water temperature (cold) is 90-105 at times. After my first year I replaced the membranes and cut them open just to see. They were perfectly fine. I’ve been running the same membranes for three years now without issue. That said, they are Dow membranes and not generic. There’s a lot of us here that have rodi with hot incoming water, some have the units in the garage like me, others have them inside. Either way, there’s no way around having hot water going through the membrane during the summer and I haven’t heard of anyone chilling thier incoming water yet. Your results may vary