My husband and I have a Lennox gas fireplace. After 3 weeks of us fussing with the ceramic logs, I *THINK* we finally got them in the right order. (seriously, sometimes I think we are too stupid to own a home - we're the first owners of this house) We have a 100 lb tank outside. It was filled last year but we never used our fireplace. This year - probably since Thanksgiving we have been using it occasionally - maybe for 4 hours at a time once a week. Over the holiday break we used it quite a bit - probably 6 hours/day for about a week How long will a tank of this size last?