Don wrote:I believe its just plain not true that the kaa6 runs better is built better or is in any way better than the kaa2. They are different for a reason, big house big boiler small house small boiler. Before i bought my boiler I took the keystoker tour with one of the owners who has heated his house for decades with a kaa2 . After a great tour and a through explanation of his products I was convinced to buy a properly sized boiler . Do your homework .