I can't speak for harmon, but with the Leisure line we gain about 20% more. your chimney draws x amount of air when it is working properly, as it get hotter and it gets colder outside the draw of the chimney increases. As the chimney draws harder and harder it needs to get air from someplace. Without a baro it will sometimes reach into the hopper to get its needed air, but because of harmans feeder design, I don't think you need to worry about this. When you use a baro, it lets room temp air in and mix with the 500* stoker air. As a result, the temp of your chimney lowers and causes less draw. BINGO, it keeps the hot air in the stove a little longer letting the convection fan do its job better.