Well, go figure! This one works running NG! So pleased I don't need to go through anymore challenging communications with seller. For what it's worth, I did visit a couple of the Chinese manufacturers websites and they all list these heaters as available in LP or NG varieties, so they must know there is a difference. But why this one works and the other one refused to I am not clear. At any rate I've got a dedicated outside mobile LP unit and an NG unit in the garage all for a total of $150 including shipping.... I'm happy with the outcome.... finally.