Thanks for the replies. I'm leaning with Mongo on this, as others have told me the same. The burner is not only heating the air, but the actual structure, so the next few weeks things should slow down (I hope).
This was the first time the heater has been on, and I know that 242 gallons were in the tank initially (from the fill slip), so 1/4 used should be in the area of 55 to 60 gallons as Mongo states.
I'll let you know what the next week or so brings. Thanks for the replies!