I purchased an harman Invincible T model a few months ago. I have been trying to run this stove at high output and can't seem to get more than a bag every 11 - 12 hours. I believe I should be able to burn double that rate. The heat exchangers gets sooted up pretty fast (1 to 2 weeks) with light fluffy black ash. I've replaced the door gasket with 3/8" rope gasket, hopper gasket with some rubber weather stripping. I generally perform a full seasonal maintenance every 1 1/2 to 2 weeks but have yet to achieve a good burn rate. The unit is currently direct vented with 3" PV. 1 90 deg on the back of stove, 3ft section going up 1 90 deg to outside, with a 3' section. No cap currently. Originally the unit ran hot, and shut down on over temp when I first hooked it up. The unit was leaking air through the hopper door, front door, and a small leak in the cover gasket on the side of the auger in the back where the feed rate screw is. The main leak was the hopper gasket, causing too much air to enter and it overheated. I am unsure if the hopper in this model should be completely sealed off, which is what I've achieved with rubber weatherstripping. I've cleaned and checked the combustion motor several times. I've removed the burn pot and checked the gasket and cleaned it out. I'm at a loss as to what else I can check. I have noticed that the right hand side vent seems to run cooler than the left even when it's just been cleaned, and it gets worse as the week goes on. The right side glass also accumulates some black soot. I burn ~ 2 bags a day, every day and I can't seem to burn any faster. I'm very fustrated and don't know what else to check. Thanks for your time.