Yes martyinmi the motor actually creates a negative draft in the fire chamber. the air is drawn from outside the building, through the boiler to the front coller were it travels counterclockwise around the air coller to the secondary air inlet [top] then to the primary air inlet [bottom] as the air tavels around the coller it gets super heated before it enters the firebox, makes for good combustion. from there it is pulled through the first 4 passes of the heat exchanger pipe and it is pushed out the last pass exhaust straight out the building, no need for a vertical flue. the nozzle was bought online precast, works good. a person could build that out of fire brick, which i thought about but they are expensive also. it is very easy maintinence, but i need to make some kind of flexible type brush to follow the pipes vertical to clean them. i've only been able to clean the horizontal pipes thus far, so i know i'm losing performance there plus my exhaust temps will go down and i will gain heat transfer. don't seem to matter what kind of wood i burn, it all burns hot. best wood burner i ever built, and i've built my share . Thanks for the compliments and the interest.