First impression is why is the lo on the aquastat set and 190 and the hi set at 160. This is backwards unless you want to maintain a very hot boiler all of the time. A 190 degree hot boiler will create a lot of standby loss.
Second, A schematic might help more to analyize the problem. I am not sure what the three way valve is for on the boiler.
Third, think about installing the flue like this: AHS S130 : Barometric Damper and Flue diameter question
A quick change with some 5" pipe and elbow, 6" tee and a reducer. Reuse the barometric. Then set your draft with a manometer.
I don't see any insulation on the piping around the boiler. This will create heat loss.
Running a control wire between the house and boiler to cycle the boiler on when the pump calls for heat will reduce the standby losses of the boiler.