There was a thread about that a couple of weeks ago, when it was real cold here. There is one in my S-250 shelter, which was originally setup as a psy ops shelter. It is coming out as soon as I get some cable raceways removed. According to what I found out about my shelter, it was older technology and has not been used in about a decade. When I get mine out, I'll weigh it and maybe we can come to a meeting of the minds.