The model tag says NAT for fuel supply but it was attached to propane. 264,000 BTU in and 198,000 BTU out. I have been seeking information/manuals for 2 months. No response from Raypak. I was tild the unit works but i dont want to fire it without first reviewing operation procedure. Any help or at least advice would be greatly appreciated. jeffdreffs@hirotecamerica 810-656-2643