K79 Oven Build

[deejayoh]

Re: K79 Oven Build

You need to use firebrick for your vent. It will get very hot, as all the gases escaping from the oven go through it. There is flame going through there too when you are firing the oven.

You can use normal brick for a decorative arch at the front of the oven.

For the amount of brick in the vent, you are probably only looking at $10 or $15 cost difference to go with firebrick

[V-wiz]

Re: K79 Oven Build

All good points.

[K79]

Re: K79 Oven Build

Is there any limit to the length of your vent landing? I was looking at making mine 12". Didn't know if that was too long or if it's just personal preference. I'm thinking of having a 8" dia. metal plate fabricated and using that for my flue vent, then adding clay flue liner above that and bricking around that. Trying to make my flue vent nice and big. The clay flue liner I'll be using is 8" x 12".

[K79]

Re: K79 Oven Build

I'm trying to figure out my vent and arch design. Having no experience with laying brick I have concerns with it being stable. Please let me know if this design looks stable, and if the vent landing and vent itself are sized ok for a 40" oven. They are a little different than the FB plans. I'm going to be using 8" x 12" clay flue liner and buiding up around that with brick 3' high.

Thanks all.

[K79]

Re: K79 Oven Build

As everyone here knows by now I tend to over analyze things a bit. I had to get the pre-construction nerves, jitters, and just a sense of being overwhelmed out of my system. I picked up a few bricks just to see how they would cut and I feel a lot better now that I have a feel for it. I won't be using any of these and my soldiers need to be cut at an angle but here they are

[mrchipster]

Re: K79 Oven Build

Is there any limit to the length of your vent landing? I was looking at making mine 12". Didn't know if that was too long or if it's just personal preference. I'm thinking of having a 8" dia. metal plate fabricated and using that for my flue vent, then adding clay flue liner above that and bricking around that. Trying to make my flue vent nice and big. The clay flue liner I'll be using is 8" x 12".

Limit of the vent landing is personal preference, Some people like to be right up near the oven and have easier access to the interior with a minilmal flue arch and zero or near zero landing.

I decided I would like a place to set things. prior or just after leaving the oven, and I have a rounded cantiliever after my decorative arch. I will be completing the landing this spring when it gets a little warmer.

I do wish I had flaired my flue arch or made my reveal on the inner arch a little larger as I would like to have a better seal at the inner arch and the door just barely fits into the flue arch. I actualy need to turn it slightly when puting it in and out so it does not get stuck.

My flue floor is slightly lower than the interior of my oven to aid in this transition, .125 inches,

You may want to consider the design of your inner arch to have the brticks reach back int othe oven it appears that your inner arch is designed with very thin bricks and this may create problems with inner arch to dome transition near the top of the inner arch.

Chip

[K79]

Re: K79 Oven Build

how much reveal does yours have?

[K79]

Re: K79 Oven Build

Does this look ok? 4" for the arch stones? Also does it look stable to you? I'm concerned about the area mentioned in my previous post.

[deejayoh]

Re: K79 Oven Build

I can't tell 100% from the picture, but your outer arch should overlap your inner arch a bit. You can't have that open end on the back of your vent. Overlap by a third of a brick and it will give it more strength + you will have more room for your chimney without having to go to a deeper landing.

[K79]

Re: K79 Oven Build

I'm modeling my oven off of Ken524's to some extent. I'ld like to make my arch roughly the same as his, but I wanted the vent opening a bit larger. Maybe I don't need it larger.

This is a picture of Ken524's oven. Thanks Ken.

[deejayoh]

Re: K79 Oven Build

I remember looking at Ken's dome when I had this question too!

While I know that Ken's oven is plenty strong, I went with a full arch in front of and behind the vent for a couple reasons

1) I thought it was stronger in the long run
2) probably more importantly, I wanted to incorporate a heat break, which I could not see a way to do with that design.

I didn't take a lot of pictures of my arch during construction - but here is one that will show you my approach. I cut some "L" shaped bricks to wrap over the inner arch. (note that the "L" bricks shown here are WAY too small. I only did that on this course, the rest of them were much longer.)



My design shifted the vent a bit toward the front of the landing vs. Ken's, and I was able to get about 1.5" of overlap over the inner arch. I have a 10" deep landing with about a 5 x 10" vent. So that gives me about 2" of brick arch on the dome side of the vent + 1.5" overlap of the inner arch, and about 3" of brick arch on the front side. The "L" bricks also leave about a 1" reveal on the inner arch. I left a ~1/4 space between the outer and inner arches where they overlapped - and stuffed that with refractory rope before I closed it up.

Personally, I would highly recommend the heat break if you think you will be baking in your oven. IMHO the exposed landing is the biggest source of heat loss in the oven assuming you've done a decent job of insulating the dome.

/soapbox

[K79]

Re: K79 Oven Build

Ok, can you explain the heat break you're talking about? That's confusing me. You must have a pretty decent lip around your inner arch for your door to seal to. Any way to take a photo of your vent so I can see what you did with the arch. That photo gives a great idea of what you're talking about but what do you do for the vent?

This is a photo of MisterToy's vent. What's the difference structurally at the vent than Ken's?

[deejayoh]

Re: K79 Oven Build

I'll try

First off, a heat break is an air gap between your inner and vent arches. The theory is that the gap will decrease the amount of heat that leeches from your dome into the arch/landing. Since the arch/landing is an large exposed mass of brick (i.e. there is no insulation on the inner surfaces) it makes quite a bit of sense. It's kind of caught on with builders in the last year or two, it seems. Most professional ovens have them, and lots of folks here have been incorporating them in their builds. I don't think they were generally discussed when Ken built his oven.

So the gap you seen in the "L" in my previous post is my air gap. It goes all the way around the arch. The "reveal" (the lip) is the space covered up by the plywood form in that picture.

You can see the reveal in this pic I just took (all sooty and all!). It's 1.5" all the way around

Here it is with the door in place


I stuffed the reveal w refractory rope and caulk when I was done in order keep the smoke where I wanted it. Thus far, no issues - and the surface of my arch is always quite a bit cooler than the bricks right next to it.

As for mistertoy's vent - hard for me to tell in that pic. It does look like he built the arch with support on either side of the vent - whereas Ken used the inner arch as the back side of his vent. When you do that, you have a single plane of failure for that mortar joint. It's just one big long mortar joint, no staggered bricks. If it starts to crack, it will run all the way along that plane and your arch is now separated from your dome. Does that make sense?

[K79]

Re: K79 Oven Build

so your entire vent area is sort of "free standing" from the rest of your oven right? Everything from your inner arch out is not attached by touching bricks or mortar.

[deejayoh]

Re: K79 Oven Build

so your entire vent area is sort of "free standing" from the rest of your oven right? Everything from your inner arch out is not attached by touching bricks or mortar.

It was when I built it

Check this post, you can see that I buttressed it with cement blocks mortared to the base. Used an IFB between the vent arch and the cement block to prevent heat loss. I didn't trust it to just sit on the insulation. It rocked a little bit, so I buttressed. Probably a good idea with the arch anyway, since the sides aren't locked to anything.

http://www.fornobravo.com/forum/6/st...tml#post132930

Others have taken different approaches to the heat break. Not everyone has the overlap, some are just built freestanding next to the inner arch. You'll find that after finishing a dome, it's not too hard to build it this way.