I would like to install a jotul direct vent propane heater at 7800 feet.  Currently the heater is operating at 3000 feet and doing a great job.  I have read that the non vented heaters have issues with the pilot light staying lit.  Does this  happen with the direct vent heaters?  Are there any other issues I need to know about with elevation? and free standing propane heaters?  Thank you!