I am just finishing up installing 2 Lochinvar 400,000 BTU/h boilers. There is a barometric damper on each boilers vent pipe(negative draft) right before they T into the main vent pipe that goes to the roof. Right now when I fire boiler 1 the damper for itself opens as it should. When I fire boiler 2 the damper for boiler 1 opens. I have not yet calibrated the dampers and am curious as to how you calibrate them?