outside the collar is 12 and 7/8" exactlyfranco b wrote: ↑Tue. Sep. 22, 2020 2:07 pmUsually the pipe fits over the collar. With modern pipe you might have to flatten the seam on the end to make it fit. Stretch a piece of string around the collar and measure it .If it measures 12.56, four inch pipe should fit. Furnace cement is very brittle when dry and cracks off easily when dry.
do I need a custom pipe?