Offset Chimney

[terraVista]

Hello,
I am just finishing up the dome for the oven that I am building and I have a couple of questions. I have been building the oven according to the "Bread Builders" book. I am wondering if it is possible to have the chimney offset from the doorway. I understand that the gasses need to move quickly out of the doorway to create the proper draw. I intend on using a eight inch pipe for a vent and plan on having the chimney about eight feet tall. I would like to have the chimney at the front corner of the oven about 27" center to center. This is for aesthetic reasons. How can I make this happen?

My other question is where is the best place to position a thermocouple in the oven. THis oven will be used for bread and for pizzas.
Thanks

[staestc]

Re: Offset Chimney

Your flue needs to start directly above and in front of the door. I see no reason why you could not angle from there towards the corner, then go up from there, but a steep angle might slow down the length of time it takes for the flue to heat up and start working properly. I would think you might have smoke rolling out the door for a bit until the flue heated up enough to start drawing properly.

Just my two bits,
Travis

[terraVista]

Re: Offset Chimney

This is currently what I am thinking for the design of the flue and smoke box. I would appreciate any info about the feasibility of this design. I am a pretty good welder and plan on welding the smoke box. Does it matter if the flue is based off to the side of the smokebox? does it need to be directly above the smoke box?
Here are some photos of the setting of the oven and the current progress

[Wiley]

Re: Offset Chimney

Here's a thought and I only toss it out since you said you were a welder: Fabricate a hood such that the gasses escaping from the left hand side of the entrance door move up at an angle to the right. Perhaps that's not clear, on your drawing the top line of the cross section of the chimney makes a dog leg, instead make it a straight line from the top left to the actual connection to the vertical chimney. You could build the whole thing out of ten guage plate; front and back plate and constant width strip to separate them. Probably be easier to build. Your drawing has the whole assembly covered by stone so it wouldn't be any more visible than what you have.

The advantage of what I'm suggesting is that the gasses don't have to move horizontally before they start moving upward.
Bests,
Wiley

[terraVista]

Re: Offset Chimney

That sounds like a pretty good idea. Anyone have any thoughts about this or have any other ideas?
Thanks

[dmun]

Re: Offset Chimney

It looks like your oven is attached to the house, meaning that your oven may have to conform to code. Code is pretty clear, you can have two bends in your flue, not to exceed thirty degrees, in order to offset the chimney top from the firebox. Horizontal runs are not allowed because you can't get a chimney brush down them. You'll have to also maintain close attention to "clearance to combustibles". You can read the IRC pertaining to masonry fireplaces (the code applying to brick ovens in residences) at rumford.com

[terraVista]

Re: Offset Chimney

The oven is not attached to the home. I looked into the code before construction. It needs to be 2" away from any structure and the chimney output needs to be 3' above anything within 10'. It will be with the chimney offset to the corner of the oven. The code is not so clear for the chimney elbows as far as a outdoor fireplace is concerned. Is it necessary to be able to clean a pizza oven chimney? The Interior code is clear. My concern is that the design that I am thinking of will properly draw and make the oven work well. Any thoughts that you have to make that possible would be appreciated.
Thanks

[nissanneill]

Re: Offset Chimney

Hi terraVista,
I have put a diagram of an idea over your original .pdf diagram.
The chimney void could be made from 304 stainless steel, around 1mm thick, (easily welded) to flow the smoke and gasses in as a direct line as possible under the constraints of your build. I would make the flue at least 8? as a 6? would not handle the amount of smoke until it got hot to draw as you hope. It would be very easy to dynabolt onto bricks both over your oven doorway and also the back of your face arch.
The diagram speaks for itself and would be a breeze to make.
My 40" Pompeii void and 8" flue are centrally located and symmetrical and it draws a treat.
Food for thought!.

Neill

[staestc]

Re: Offset Chimney

I like that shape Neil. It has the advantage of appearing to be releatively easy to clean from the oven side as well.

Travis

[dmun]

Re: Offset Chimney

Freestanding ovens are considered backyard barbeques, and are not covered by code. You still want the most direct flue path for your smoke to travel. Sometimes building code is the distillation of experience and common sense. I'd avoid a horizontal smoke path.

As to your flue cleaning question, pizza ovens burn at such hot temperatures, and with ample air input that they don't build up chimney deposits like smoldering all night wood stoves. Still, you should be able to clean it if need be.

[terraVista]

Re: Offset Chimney

Thanks Neil,
That looks like exactly what i am looking for. I really appreciate your time on this. I'll post some pics as it comes together, unfortunately our winter is rapidly approaching and I'm going to have to build an inclosure soon.

Do you have any experience with thermocouples? I have one and am trying to find out where the best place to mount one is. Is it in the hearth or in the wall?
Thanks

[terraVista]

Re: Offset Chimney

Hey All,
I've since looked through most of the thermocouple threads and still don't feel like I've found an answer to my question. If I have only one thermocouple and I will be cooking both Pizzas and Breads where is the best place to locate this device. Hearth or the in the dome? Would it be better to try to read surface temps or Soak?
Thanks for your help
Eric

[nissanneill]

Re: Offset Chimney

Hi Eric,
with regards to your single thermocouple location, I personally would not waste my time nor money (not that they are expensive though).
I have 4 in my Pompeii, 2 in the floor and 2 in the dome to measure the just below surface temps and the soak of the bricks. I even bought a 10 thermocouple switch from the UK, hooked it all up and have no need to use it.
Since you have a single one, (as you are so keen to try it), then I would , set it beneath the centre of the hearth brick floor to measure the bottom of the floor, or the soak. I chose this because you can measure very accurately the surface temperatures of both any part of your hearth and dome surface temperatures but not what it is at the other side of the brick.
I am not saying that they are a waste of time, effort and money, BUT, the more you use them with the oven, then the easier it is to determine the temps with time, fire ferocity and general experience, what the temperatures are and how far the heat has penetrated the bricks.
If you are a 'serious bread baker', then the information from more than one single thermocouple will give you the ability to accurately determine how many bakes and how much per bake as well as where to locate your goods within the oven for success.
They are almost useless to cook pizzas as you can measure the hearth surface temperature and you can watch them cook as well as check under them for degree of 'cookedness' (if such a word exists). As the oven cools (and is verified with a laser thermometer), you cook longer, until is to your satisfaction. You cannot do this with a closed bread oven and you can't check the degree of 'cookedness' until you remove the bread, allow it to cool and cut or break it open. If you got it right, then you were very lucky , extremely talented or had blind faith in tour multiple thermocouple information.
I also played around with the vent illustration and as I would make it. Very easy to do but may need some cuts in the rolled edges on the LH and RH sides if you don't have access to a Jenny. A few tacks of weld, a large hole cut in the top, the ring welded on and done!!!!
Oh, incidentally, I always make the top hole large enough to fit the shrunk end of the flue but not the flue diameter! The flue sits on the vent but cannot slip through the hole, making securing unnecessary.

Neill

[dlgeis]

Re: Offset Chimney

My Scott oven has a brick smokebox about 26" wide by 8" deep and my 8"double wall flue sits on the far left edge. This allowed me to clear the roof ridge. The smoke box is about 14" above the vault exit. I do have a small amount of smoke exit the outer door on startup but I don't believe it is affected by the flue location. If I were concerned about it I would make my outer opening no higher than my vault opening (mine aches about 5" higher. You could light a small newspaper torch under the flue when beginning the burn to start the draft.

I am using only 4' of chimney so yours should draft even better. Now that I know about top down fires I believe I will have almost no smoke exit the door even during startup.

DG