We've got a place we camp at just over 10,000 ft. in Cali. A few years back I invited a friend to go camping in June with us. Me, the wife and 2 dogs was all the tent heat I needed. He, brought a brand new mr. buddy heater. We go to bed the first night of a planned 3 nighter, and all night long I hear the mr. buddy striker lighting up. About 5 in the a.m. I hear the friend moving about, and I get up to see what is up. It is frosty cold, to say the least. He is sitting on a rock, down by the lake, trying to catch the early morning sun coming up, cursing the new mr. buddy heater. He couldn't believe a brand new heater, out of the box, didn't work. We go up to check it out, and I start laughing at him as I read the box. In big letters, it says, 7500 ft. is as high as it will work due to the low oxygen sensor. Needless to say, 1 night was all he wanted, and for some reason, he won't go back up there any more unless I loan him a dog at night. :)