I would really caution against assuming you are burning 1000 calories exercising. This is not to be mean or obnoxious, but to relay the very realistic possibility that you are overestimating your exercising (and therefore deficit and expectations about weightloss).
For most people, running for 30 minutes straight burns around 300 calories. Of course, individuals who are heavier may burn more. Strenuous aerobics classes may be around comparable. Ellipticals, exercise bikes, walking, yoga/pilates, etc generally all burn less.
By these very rough estimates, it takes around 1 1/2- 2 hours of intensive exercise to burn 1000 calories.
As a previous poster said, it's impossible to apply an equation to weight loss- each body is different and burns at different rates. Even heart rate monitors and body buggs are notoriously inaccurate.
That's why weight loss is a lot of trial and error. Play around with 1300 a day- if you feel good, are losing weight, and getting in ALL your nutrients, go with it. If you feel weak, lethargic, or too "deprived" (and then make bad eating choices) up them a bit.