Why does nobody talk about how much pitch buildup changes draft over time

I was cleaning out a chimney last week for a lady in Portland and I swear the draft felt different than what I expected based on the flue size. So I got curious and looked up some old manuals from the 70s and found out that even a 1/8 inch layer of creosote can reduce cross sectional area by like 15 percent depending on the flue shape. That blew my mind because I always just scraped till it looked clean but never thought about how the smoke flow actually changes month to month. Has anyone else noticed a big difference in how a chimney pulls after a heavy buildup season vs right after a clean?

3 comments

3 Comments

the_eric17d ago

Guess that shiny creosote was playing hide and seek with your draft.

the_holly17d ago

Bet that stuff gets real toxic if you burn it without knowing it's there.

lucasw8417d ago

Oh man, this is wild timing. I was helping my buddy clean out his parents' old wood stove setup last fall and we kept noticing the fire would just sit there smoldering even after we thought we got everything off the walls. Turns out there was this super thin glaze of that shiny hard creosote that you can barely see but it makes the flue feel like it's half the size. I had to run a chain knocker through it three times before the draft finally opened up.