How many calories you burn depend on a hell of a lot of different things, including but not limited to your genetics, weight, type of activity, intensity level that you exercise at, what you ate beforehand, what you eat afterwards, etc. But as a generality, michael phelps swims for what, 6 hours a day? and he eats 15,000 calories every day. So that should give you the answer you are looking for.

Back when I was doing construction, lifting crap for 8 hours a day in the hot sun, I was eating anything and everything I could, and drinking about 6-8 beers a night, and losing a few pounds a week. Rememeber though, I have a different genetic makeup than you. +4