I just don't know, haven't been that high since we got them. Spent the first three months of this year at about 4400 ft, then all over Alaska, but not real high, and it was summer anyway. Right now we are sitting at 47 ft, and in a couple of weeks moving to an old Army Fort that is probably a little bit lower.

One good feature is that they have a low oxygen shut-off, so you can't do yourself in that way. Still, we only use then when we are awake. Saves propane that way also...