I have begun installing my new vigas 40 in my basement. Ran into a small problem and I'm hoping someone can point me in the right direction. I am going to disconnect my oil boil in vent the vigas into my chimney, however the clay lining where the boiler connects is only 7" (the flue going up the chimney is a 12"X12"). The vigas needs to have a 8" vent. How would I go about increasing this portion of the chimney. Just breaking out the liner and cutting the brick out to accept a 8"?