Hi Sunshine,
To be honest, I have yet to be convinced why I should invest in a hot water system through cleaning. I admit I can see the benefits for the winter with freezing but having said that it is still alot of money.
All my vans use cold water and through the winter we instal water heaters to avoid freezing.
As for cleaning windows, it is fine with cold water.
I would look around and do some homework before buying, there are a lot of good sytem options available.
Best of luck,
Trev