HP21. All in all works great. The one annoyance is the pellet hopper transition from the bin sidewall to the auger is not steep enough to allow the pellets to flow to the auger, reducing the usable capacity of the hopper by 1/4 to 1/3rd. I've tried different brands of pellets and see no difference. Did not see this issue with my previous stove, a St. Croix Lancaster. But that stove is not as wide, so the slope in the transition is steeper. The thing I love most is it is very easy to clean both when the ash pan fills and during the season and end season for general maintenance.