Hello, I have two pellet stove installations at my home. One is working great and the other one that was installed before I bought the house had never worked well. The installation is on the first floor. The pellet stove is a Whitfiled Tradition 2004. The vent diameter is a 3 inches. The pipe is in a vertical direction. The equivalent lenght, including all elbows and everything is 25-27 ft. The area where I am located is about 700 m above sea level. The cap termination is under the roof line. The flame is lazy and the burning pot gets plugged with partially burn pellets after an hour or so. The glass gets coverred with soot. I have cleaned everything in the stove, cleaned the vents and pipes, but nothing seems to work. If I open a window and install another blower close to the combustion blower, it seems to get better a bit, but no significant change. The installation was made by professionals. I wonder if the stove is the problem...or if its a design problem with the venting system. I have made some calculations, and the pressure loss would be reduced significantly by increasing diameter to a 4 inches. I wonder if increasing the pipe diameter will fix the problem. What do you think ? Is it a stove problem or do you believe I increase vent diameter to 4 in ?? Also, anyone has an idea of what should be the targetted pressure in the piping during normal operation (pitot tubing measurement). The other installation I have is located in the basement and pellet stove is a Harman P61....it has been working great for 3 years. Thanks for you help, this is very appreciated.