Just learned how many bricks are in a standard chimney flue

I was cleaning out a flue on a 1920s house in Portland last week and got curious. I looked it up later in an old trade book I have. A standard 13x13 inch flue liner is made with exactly 72 bricks. Not 70, not 75. Seventy-two. I always just slapped them in there and never counted. The book said it's because of the standard size of the clay liner molds from back then. It's such a weirdly specific number to be the norm. I told my partner and he just stared at me like I'd lost my mind for caring. Has anyone else ever come across a random, fixed number like that in the old building specs?

2 comments

2 Comments

the_robert2mo ago

Honestly that's the kind of fact I'd hold onto forever. Tbh old trade specs are full of that stuff, numbers that just got locked in because of some machine they used back then. It's cool that you actually looked it up instead of just wondering. My partner gives me that same look when I go on about concrete mix ratios.

miller.jason2mo ago

Yeah but that's the part I find kind of sad, honestly. Those old numbers got locked in for a reason, and we just forget why. It's not just a cool fact... it's a lost piece of the story. If we don't ask why, we're just passing on a number without the meaning. Then it really is just a random spec, and the guy who figured it out might as well have not bothered.