It's hard to tell in the photo, but a friend of mine has a vigilant that looks about the same size. His is a whole new stove since I went over and encouraged him to fill 'er up. It doesn't make it hotter, that's controlled by air inlet, but it gives it the fuel it needs for a longer burn. But, now that he's learned to fill it up, he does run it hotter also.
It looks like you might not have a barometric damper. It's possible you are losing a fair amount of heat up the chimney.