My friend Russell has been installing rocket stoves here in Ladakh at 11,500 feet, and is starting a business to make and install them, along with some Ladakhi friends of mine.
Himalayan Rocket Stoves
We made a couple of rocket cookstoves at our school at 10,500 feet, and they worked but we didn't work out the design completely so we had problems with ash buildup and smokeback. But it seems they'll work if we do them right. Ours were J-type, I guess. Russell's are, too.