Fireplace/oven planning stage

[bimbo]

I have just spent the last few hours searching for designs on fireplace and oven combinations but seem to be able to find very little.
I have been given permission by the wife to build an WFO oven on the proviso i build her an outdoor fireplace and due to space restraints it will have to go ontop of each other so I have been racking my brain trying to work out how it can be done.

There unit is going into a corner so i figured 1 option is to vent out the back of the fireplace and run the flue on an angel to come out in the triangle space at the rear of the oven (i am building a 36ish dome) but this would mean the fireplace would be very deep.

Other idea i just came up with was to set the oven back a little like this photo Pizza Oven Photo | Stockton and have a shallower fire place and run 2 smaller flues through the hearth slab and up the outside on either side of the oven arch and merge into the ovens flue. This would all then be hidden by the exterior brickwork.

Is there anything obviously wrong with either of those designs?
Will 2 smaller flues draw just as efficently as one larger one?

any other suggestions and critisism is more than welcome

Cheers
James

[bimbo]

Re: Fireplace/oven planning stage

I should also clarify that they wouldn't be running at the same time or trying to use the fireplace to heat the oven in anyway.
I would imagine that on a cold night that once the pizzas have been finished that you may be able to pull the coals out and put them in the fireplace for a bit of heat for the area.

[70chevelle]

Re: Fireplace/oven planning stage

Here's a link to my thread http://www.fornobravo.com/forum/21/q...ry-4547-2.html It takes a little planning but definitely can be done. I've really been enjoying both the oven and the fireplace, sometimes at the same time. I baked a load of hearth breads a week ago, when it was in the high 30's. The fireplace was very enjoyable as I was baking outside while the snow was falling.

[bimbo]

Re: Fireplace/oven planning stage

Thanks for the reply. Your oven is the only one that i found that has done it that had some information about the build and how you vented the fireplace.

So far i have spend all my time reading about oven plans and why some designs are better than others etc so i guess now i need to do plenty of reading about fireplaces as well.

Can anyone tell me the main reason fireplaces are vented at the top back?

[dmun]

Re: Fireplace/oven planning stage

Can anyone tell me the main reason fireplaces are vented at the top back?

They are vented at the top, because smoke rises. The vents are at the back to direct the smoke away from the wide front opening. The Rumford fireplaces are so shallow that the vents are pretty near the front, and if you bring the firebox forward beyond the wall plane (like to put a mantle on top) your vent can be flush to the wall.

[cvdukes]

Re: Fireplace/oven planning stage

Other idea i just came up with was to set the oven back a little ... and have a shallower fire place and run 2 smaller flues through the hearth slab and up the outside on either side of the oven arch and merge into the ovens flue. This would all then be hidden by the exterior brickwork.

Is there anything obviously wrong with either of those designs?
Will 2 smaller flues draw just as efficently as one larger one?

James

For all practical purposes, 2 flues will draw about like one. You run into slight frictional-velocity differences because of the extra surface area of 2 flues instead of 1 with the same cross-sectional area (partly the same reason that a circular flue is more efficient than a square one), but generally not too important for the level of efficiencies we tend to accept in our outside chimneys.

The real problem would come in once the combined flue above the arch starts to draw. As I understand your design, the main flue would be open to the oven's antechamber. Hot air from the fireplace would rise up the two outside flues and continue up the main flue. This movement up the main flue would create a vacuum on the opening in the antechamber. If the oven wasn't fired at the same time, the vacuum would draw in colder air into the main flue. Because of the colder air density, the main flue would start having some issues...I would suspect that it would set up a rythmic chugging ...periodically dumping smoke back into the antechamber.
It might be kinda of interesting to watch! You could put some dampers in to seal off the antechamber when the double flues were running...other options would be to just continue the double flues up alongside the oven chimney to the top (for a wide chimney look) or even join them into one main flue that runs up along the back side of the oven chimney. For short runs, you can easily divert smoke upwards at angles 20-30 degrees above horizontal...

[bimbo]

Re: Fireplace/oven planning stage

Ahh a very good point about merging the 2 flues into the main oven/fireplace flue. But i could either put in some form of damper in the main flue to stop it drawing fromt eh oven whent eh fireplace is running or just run a 2nd flue right behind or beside each other.

[bimbo]

Re: Fireplace/oven planning stage

Still trying to get my head around what needs to be done and the design of the fireplace.
Does anyone have any good fireplace design websites other than rumford?

Construction of the whole deck etc which will contain the outdoor fireplace, BBQ and Pizza oven is due to start in a few weeks time.

[bimbo]

Re: Fireplace/oven planning stage

How will this design work?


hoping to be able to use 2 smaller flues which will go up either side of the arch for the pizza oven.
The fireplace will be build out of solid pressed clay bricks bult inside the block stand for the oven. What material can i use for the roof of the fireplace? is normal concrete suitable or does it need to be a special type of cement?

would this design be better with or without the flat piece just below the chimney. my thoughts with that where to stop all the heat going straight up the chimney and i have read that a wide but thiner area creates a better draw (is this correct?).
I was planning to make it out of thick steel and removeable just incase it adversly effects the draw of the fireplace.

Is this a good design or heading for failure

Your thoughs
James

[dmun]

Re: Fireplace/oven planning stage

Is it an indoor or an outdoor fireplace? (will you have to worry about dampering?) This would be a big factor in your "heat running up the chimney" question.

Is there any reason why a single offset flue wouldn't work as well as a split Y shaped one, and have the virtue of simplicity?

I see you have an arch drawn as the top of your firebox. I think a brick arch would work fine as the top of your firebox, and the bottom of the smoke shelf. I'd alternate the bricks so you didn't have running seams going across, as in the usual practice for barrel vault ovens.

[bimbo]

Re: Fireplace/oven planning stage

It is an outdoor fireplace.

yes one offset flue would be possible, i just had 2 cause for some reason i have to have things symetrical.

The arch in the picture labled 'front' was actually an external one to dress it up a little but there is no reason why i cant build an arch in the top of the fireplace as well. it would sort of be a 1/2 dome top on it. Is this what you where refering to?

On another note i poured almost 5 cubic meters of concrete footings and piers this morning in preperation for my deck and outdoor kitchen

Cheers
James

[dmun]

Re: Fireplace/oven planning stage

It's worth reading up on outdoor fireplaces at rumford.com:

Outdoor Rumfords

There is an inherent problem with smoking with outdoor fireplaces, because they don't have the big indoor/outdoor temperature differential.

[bimbo]

Re: Fireplace/oven planning stage

Yeah have read thoat one. Hopefully because of the design of the area that the fireplace is going it it won't be as much of an issue. The fireplace is going to be part of a deck which attached to the house and under cover. There is also going to be a wall about 1200mm high and 1500long on either side of the fireplace at right angles with the fireplace in the corner so it will be protected from breezes and the area should hold the heat fairly well.

[kat]

Re: Fireplace/oven planning stage

Hey Bimbo -- Planning on doing something similar (only not in a corner). Would love to hear how your venture is going, see pictures, learn how your flue/s function, and generally from your efforts. Thanks, kat

[bimbo]

Re: Fireplace/oven planning stage

I have just finished the oven and started the curing fires today. I would say it will probably be a few weeks till I get started on the fireplace but if you check out this thread http://www.fornobravo.com/forum/f8/j...oven-6820.html you will see the progress so far and I will continue to update it as I get more done.

Cheers
James