# Firebox Vent Opening Size Survey



## pianov (Sep 28, 2013)

I just joined this forum - I have never before had the opportunity to talk to others who smoke meat. I built my masonry side-box smoker 20 years ago and have used it ever since. I had no guidance for the design. I am trying to determine whether I can tweak some things about my smoker to make it work better. Mostly I slow smoke pork butts and ribs and the like.

Below is a picture of my smoker. The smokebox is open in the photo. The door is wood, detachable and is leaning up against the smoker. I burn oak wood in my smoker - I have never tried charcoal.

file://localhost/Users/terryfarrell/Desktop/P1010036.jpg

If by chance the picture is does not appear, here is a link to it:  P4150009.jpg

I have one question at this point:  When slow cooking a pork butt or ribs or whatever - you're trying to keep the smokebox at  220 degrees for many hours (6 to 24 hours) - what size opening do other smokers commonly have while maintaining the slow smoking described above?

The reason I ask this is that I used Feldon's BBQ Pit Builder Calculator on my smoker and it checked out - okay, I guess - or maybe not.

Here is a link to my data calculations:  Link to BBQ Pit Calculator

Seems my firebox is a reasonable size for my smoke box, although on the large size - it is almost 60% the volume of the smoke chamber. The opening between the two is small - it is 20 square inches rather than the recommended 41 square inches.

The size of the firebox vent is WAY small - it is just one square inch - recommended is 20 square inches! What's up with that? Even my 1" pipe that is my firebox vent, I have to choke down or my firebox will get too hot and heat up the smoke box too much if I don't. Where do they come up with 20 square inches? If I had that kind of vent opening, my fire would burn out in no time and the smoke chamber would climb up to 1,000 degrees!

Is the 20 square inch recommended opening used just to provide enough air for when the fire is first starting (I need to open my firebox door for the first 20 minutes or so while the fire gets going)? And then once the fire is going good most smokers with their 20 square inch vents are throttled WAY down - almost closed - for the long burn to keep the smoke chamber at 220 degrees?

So that's why I ask - how many square inch opening do you maintain on your firebox vent when smoking a pork butt for 18 hours?

I know all smokers are different and will require different settings - heck, even the weather will affect those things. But I'm trying to learn more about how my smoker works, how it should work, and whether there is anything I could change to make it work better. In another thread I started, someone recommended using a grate for my wood - I have always just put the wood on the floor of my firebox. I'm thinking here that maybe I should be making a smaller, hotter fire that sits up on a grate - and that might require more air flow - which again I read may generally be a good thing - less white smoke, more clear(ish)/blue smoke, less smoke stagnation in the smoke chamber - and it might require a larger vent opening on my firebox. Perhaps if I find that most other smokers find that a much larger opening is needed on their firebox vent, I'll look seriously at trying some different things on my smoker - specifically, using a grate, making a larger vent opening and sealing the 38 leaks I have in my firebox.

Thanks for any responses!


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