# large vertical smoker calculations

Discussion in 'Smoker Builds' started by rusticsoul, Jul 19, 2015.

1. ### rusticsoulNewbie

HI Guys,

so I have been contracted to build a smoker that is a vertical smoker with 1500 in height, 1200 in lengh and depth (all in centimetres by the way)

I have used the feldon calculator but it says I need a chimney that is like 3000 inches long?

Being that the firebox is underneath is 600 high and the same lengh and depth what size do I really need to make the opening and chimney height.

any help would be good.

2. ### dmwtx79Newbie

I recently completed a horizontal smoker with a vertical on the side. Feldon calculator went crazy when I put all my calculations in. 20" dia all the way. I ended up with a 4"dia 12" tall exhaust. The vertical part will act somewhat as exhaust too, just have to make sure you have decent flow so you don't end up with stale smoke while your cooking. I actually tried to get a few more square inches out that could go in so I would have decency flow.
Hope this helps a little

3. ### ahumadoraSmoking Fanatic

I take it you meant millimeters.  The Feldon calculator doesn't work for vertical insulated smokers, maybe we can work on making a calculator for that.  My experience is the shorter the chimney the better for a vertical smoker.  So you have a smoker 1200mm deep? I think it maybe difficult reach to the back of the grill without burning yourself.  I have found about 800mm is deep enough.  For an insulated vertical that sure is a large firebox. I have found 25% of cooker volume works fine on the ones I have built.

4. ### rob siccSmoking FanaticGroup Lead

While you are thinking about a calculation for the chimney, can you also consider hot to calculate the size of a FireBox.

5. ### ahumadoraSmoking Fanatic

Make it between 15-30% for the CC volume and you will be fine.

I have been leaning towards running the internal vents and chimney on the larger side lately.

This last weekend I cooked up some ribs with this one at my house.

I used about 1/3 bag of lump charcoal and a few splits and let it take it's time to get up to temp.

Every hour I would add about 3" diameter x 10" piece of wood and had a miserable little fire going.

Held 225F all day and had the vents most of the way open.

The firebox is probably 15-18% of CC volume .

If your smoker is not insulated then add a much bigger firebox.