Free: Contests & Raffles.
Some of the stoves out there - and I'm operating from the viewpoint of using nearly every sized Kifaru stove and some homemade, are akin to backcountry nuclear reactors. If you stoke them up to the point were they are actually working they put out a lot of heat. And 8-man with a large is a great combo, whereas a 6-man with a large stove ripping along will have everyone demanding both doors be opened wide and will come home from the trip with a very nice tan. Bottom line, you've got to get the right stove output for the shelter size.