not exactly true. If you run the mini split to where the return air of your central air is, you reduce the return air temp which in turn, reduces the load.Unfortunaltely I cannot use a window air unit. My windows all slide open sideways. I do not have double hung windows. I did look for a mini-split, but that would only cool one room, and I already have central air. So even if I have a mini split, I would still have to run the central to cool the house anyway, there would be no savings. Thanks anyway!
I am not exactly sure how much effiicency you'd loose, but aint bad. The water heater is just the easiest of the bunch to do, but resistance water heating isn't as efficent as a heat pump water heater. There used to be a company called Glacier or something like that, that would make auxiliary add on heat pump water heating... but the company has since stopped making it.