Why start a sous-vide with hot tap water instead of cold tap water?
Maybe commercial appliances are smarter than the DIY controller I put together (a more modular version of this http://boingboing.net/2011/11/04/diy-sous-vide-cooking.html) but I’ve found that when you’re starting from way below your desired temperature, not only does it take quite a while to heat the water up, but it tends to overshoot at first - it’s a lot easier to maintain a specific temperature than to reach one.
As such, I tend to mix hot tap water with a few cups of boiling water when getting things started, so I’m within 5-10F of my desired temp before I even turn the controller on. It really makes a world of difference. And if you go overboard it’s super-easy to cool things down by scooping out a little of the just-too-hot water and replacing with an equal volume of tap water.
