For my 5 gal boils I loose less than 1/2 gal over a 60 min boil. Temp is usually around 210 degrees at the top of the wort and that is with a lid covering 80% of the pot.
I then cool, take a gravity reading and add water to bring OG up to what it should be. Been working out pretty good this way.
*** Possum Trot Brewery ***
Beer Primary - Butthead Belgian
Beer Secondary - Belgian Tripel
Bottled - Big Breakfast Stout - Belgian IPA - Butthead Belgian White - Redneck Red - Moose Drool - Dirty Dubbel
Mead Primary - Nuttin
Bottled - Strawberry Trainwreck - Orange Spice - Blueberry Trainwreck