I recently purchased a peerless MI-03 Boiler and discovered I could only fit a 4" chimney liner down my chimney. The Vent off of the boiler starts at 5". Is it safe to use the 4" chimney liner? I was able to use a 5" vent for 12" up off of the boiler to a 90 degree, 18" of 5" horizontally(small incline) and another 12" vertically before I connected to the 4" Chimney liner. My HVAC contractor said I would be okay. Any advice?
I live in a two story row house