Keystone Size

[K79]

Re: Keystone Size

I was trying to figure it out building it out of clay flue liner and brick. I couldn't find anyone local that had any ideas on how to run the 8" ss stack out the peak of the roof. Issues with the weather stripping and such. This and cost has pushed me towards the clay option. would 40 sq in work with a 36" stack?

[Tscarborough]

Re: Keystone Size

Then use an 8" round metal flue, that gives you 50.26 SqIn. 36" is a short stack, so the extra will help.

[K79]

Re: Keystone Size

I have 235sqin so if I go somewhere between 35 and 40 sqin for my vent opening I should be ok.

What are your thoughts on the arch itself? I was thinking of a 36" stack... too tall? I'ld love to be able to do it a little smaller.

[Tscarborough]

Re: Keystone Size

Well, if you built that one, it would be 225.8 SqIn, so you would need a minimum of 33.87 SqIn of draw, and really more would be better unless you plan on a tall stack.

[K79]

Re: Keystone Size

Not exactly sure yet, I don't know how I'm gong to build it. A complete arch or one like the image below. I'm leaning towards the one one in this image.

[Tscarborough]

Re: Keystone Size

What size is your inner arch opening?

[K79]

Re: Keystone Size

Square/rectangular flues are measured o.d., while round ones are measured i.d., FYI.

8x8 is a common size for clay flue liners, with 30.58 SqIn of draw: 6.25 (i.d.)/2 gives a radius of 3.12, 3.1416x(3.12x3.12)=30.58. When calculating draw you draw the largest circle(s) that will fit in the area and use that dimension. The area of the flue should be around 15% of the size of the inner opening, and more is better up to a limit.

(the floor size doesn't really matter for draw)

Ok, so an 8x8 clay flue liner will work. So I need to reach at least 30.58 SqIn for my vent opening as well? A little confusing when most try and reach somewhere between 40 and 50 sq in.

[Tscarborough]

Re: Keystone Size

Square/rectangular flues are measured o.d., while round ones are measured i.d., FYI.

8x8 is a common size for clay flue liners, with 30.58 SqIn of draw: 6.25 (i.d.)/2 gives a radius of 3.12, 3.1416x(3.12x3.12)=30.58. When calculating draw you draw the largest circle(s) that will fit in the area and use that dimension. The area of the flue should be around 15% of the size of the inner opening, and more is better up to a limit.

(the floor size doesn't really matter for draw)

[K79]

Re: Keystone Size

Ok guys running into sort of a dilema designing my vent. Since my oven is 40" dia. I need an 8" dia. steel chimney. Well I'ld like to make mine out of clay flue liner which is 8"x 12". I was told that the 8"x12" has the same draw as an 8" dia. steel chimney. Others I believe have taken the 8x12's and cut them to be 8x8??? Is that enough size for correct draw?

[deejayoh]

Re: Keystone Size

Yeah, you want to use mortar on the keystone just like the rest of the dome. That's what holds the bricks apart to give your dome structural integrity. Plus, it keeps the smoke and heat inside, which is kinda nice

[ATK406]

Re: Keystone Size

No harm in using mortar to seal it up and lock everything in place. The rest of the construction uses mortar, no reason to stop on the last piece.

[K79]

Re: Keystone Size

If your keystone is multiple pieces should you put them together dry and slide them in place with no mortar? Same goes for one piece if you can. Should you slide that in without mortar too?

[deejayoh]

Re: Keystone Size

As an aspiration, that looks great. But just be prepared to make adjustments along the way! Your oven is not going to come out precisely as you draw it. My keystone turned out pretty small (relative to many), but I really only started to plan it when I got to the last three courses.



My $0.02 is that you might want to plan for the plug to be a little bigger than what you have now, because your mortar joints are more likely to be too big than too small, eating up any wiggle room you have.

[K79]

Re: Keystone Size

Ok, my keystone changed (on my plans) due to the change in brick dimensions. Does this look ok overall? My firebrick is 9x4 7/16x2 5/16.

[brickie in oz]

Re: Keystone Size

I was using my bestest Inspector Clouseau accent.......