Haven't started a fire yet this year but a couple of years ago when the heater was out I would start out with about 4 cubic ft (18 deep x 18 tall by 22 wide) in a top down fire. I would usually let it burn down about halfway and top it off again at least 3 or 4 times a night. We never burned during the day and I bought it by the truckload in my long wheel base truck and it never lasted more than 10 days iirc.