Fireplace Xtrordinair has "relief ports" built into the unit. The glass is not there relief port. A 100 pound LP tank produces 1,946,800 BTU's of heat. An STR fireplace produces up to 40,000 BTUS's of heat per hour and is 85% efficient. I think you can do the math as to how long a fireplace will burn on a 100 lb LP tank. (should equal 57 hours or so). Temperature outside is also a factor. Any fireplace that is 40,000 BTU input at 85% efficiency should give you the same results.