The performance specifications are applicable to elevations up to 2,000' above sea level. Some manufacturers offer high altitude kits to compensate for lower air density at higher elevations, but for the Burnham Alpine boiler, there is no high altitude kit necessary. Instead, expect ratings to be reduced 4% for every 1,000 feet above sea level. For full details on ratings, you can check out the Alpine product data sheet in our Manuals tab, or here.