When I was contructing this latest darkroom I charted the cold water temperature once every two weeks for a full year, just to be certain I was below 68F for enough weeks to make the purchase worthwhile. Turns out my highest low came on August 11th and peaked at 66.9F. The following year it was coincidently the same (but on a slightly different date) and to my amazement even with only a 1.4F differential the unit had no problem whatsoever supplying a rock-steady 68F.
Although not really necessary, I baby mine in only two respects. First, I filter both the hot and cold lines down to 1-micron. Cartridges are cheap, and I figure it keeps pretty much ALL harmful grit out of those solenoid-driven valves. And second, I routinely purge all residual water pressure from both sides of the valves at the end of each darkroom session. That certainly can't hurt, and it might just help protect the seals over time.
I talked to Dave Hass personally over the telephone during my purchase and configuration cycle in 2003. He was pretty darned proud of these units. Ten years later and mine hasn't skipped a single beat.
Someone once wrote that if you are going to build a photo darkroom, definitely give up something else in order to get one of these. Best darkroom equipment advice I ever got.