The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Chimney? or No-Chimney?

dmrobin's picture
dmrobin

Chimney? or No-Chimney?

I'm in the process of planning to build an earth oven using Kiko Denzer's book. The topic of chimney's isn't addressed in the book, (at least I haven't found it).


Some ovens have them and some don't. Some are in the front and some are in the back. When baking bread wouldn't heat escape rapidly with a chimney. Can someone out there provide some guidance for me in my planning stage?


You should also know that I plan on using it for bread, pizza, and other types of general baking.


Thanks, DMRobin

OldWoodenSpoon's picture
OldWoodenSpoon

addresses the issue of a chimney, and in that edition Kiko Denzer points out that he, as of that writing, had changed his position on the subject. Where, in earlier editions, he recommended a chimney as necessary in the promotion of efficiency, he had moved to thinking they only made sense in limited (like indoors) situations.  Otherwise he favored the option of a "firing door" as being easier, less technical to construct, and simpler overall, while promoting that efficiency he was seeking.  The discussion is on page 94-95 of that 3rd edition book.


I have a Denzer-style oven under construction.  Well, under reconstruction anyway.  When I built it the first time I did not include a chimney with the idea of keeping construction simple.  Then I overheated it too soon, when it was not dry enough, and destroyed it.  It was functional just long enough to convince me I needed a chimney designed into my next effort.  I have it all in place now, waiting for good weather so I can build the new dome.  My decision to add the chimney was the result of how much soot I got on myself and everything that came near the oven.  I had to do something about it, and the chimney is my solution.


I took my inspiration for how to engineer things from a site called Forno Economico, which is a private web site the covers one man's oven build (somewhere in the UK I believe).  I also had trouble with my first arch design, so I've incorporated his concepts for arch and chimney into my own oven, modified to fit my very limited masonry skills, and my choices of materials. 


You might want to look at his site for some ideas before coming to any hard and fast conclusions on either design facet.


Good Luck
OldWoodenSpoon


 

CanuckJim's picture
CanuckJim

I would heartily recommend using a chimney for your rebuild, but it must be separated from the bake chamber so you don't loose heat from hit.  To my way of thinking, it should be at the front, like the ancient ovens of Pompeii, 99 percent of pizza ovens, and 99 percent of barrel vaults.  Using a chimney will promote better draft, keep the soot where it belongs (as mentioned) and contribute greatly to faster heat up times.


CJ

Thomas Parr's picture
Thomas Parr

This is a picture of my oven completed two years ago with old reclaimed "clay" bricks.  It works great and gives off a bit of smoke initially until the oven temperature comes up.  Then there is no problem.  As well as the bricks I have covered the bricks with aluminum foil to prevent the outer 2" concrete layer from sticking to the bricks thereby preventing any damage from expansion.  Over that, there is two (2) 2' layers of thermal insulation using perlite, cement, and clay.  The base is made up of 3/4" plywood, followed by concrete board and about 40 - 50 stubby beer bottles laid on their sides in a matrix of clay, cement and planer shavings.  This is followed by a clay, sand mixture with fire brick floor on top.


http://i1183.photobucket.com/albums/x464/Thomas-Parr/DSC00856.jpg


 

Roo's picture
Roo

For bread baking you will most likey do so with no fire in the cooking chamber and a door on to help keep the heat in.  Depending on how much insulation below and above you may get several batches of bread baked using the retained heat from a properly fired and heat saturated oven.  I would suspect other baking would be the same no fire door on method.


Pizzas and other fire in cooking you would want with the door off.

ClimbHi's picture
ClimbHi

Pizza and other "broiled" foods can/should be cooked with the fire going. Bread and other baked or roasted foods are generally cooked with stored heat after the fire is out and the oven is tightly sealed with a door to help retain the heat.


I've never looked at Denzer's book, so I'm not sure what he recommends. But a chimney is not strictly necessary if you're well away from other structures, don't care if the front of your oven gets smoke-blackened, and don't mind some smoke in your face when you're starting up the fire. (Hot ovens don't really smoke all that much.) Otherwise, chimneys are usually constructed just outside of the oven door - imagine building a small fireplace in front of your oven with the oven door at the rear wall of the fireplace. That way the smoke is directed up and away from you and the oven, and you can still close off the heated oven without losing heat up the flue since the flue is outside of the closed oven. I've seen ovens with chimneys in the rear -- these usually have very short (if any) chimneys that are plugged with a wooden, or similar, plug once the fire is out to help retain heat.


I have a friend who built a pizza oven with a flue opening directly into the oven. He soon regretted that decision. Too hard to bring the oven up to temp and hold the heat. "It's a wise man who learns from the mistakes of others."


ClimbHi
Pittsburgh, PA


 


 

Thomas Parr's picture
Thomas Parr

To Roo and ClimbHi:


If you open the picture on "Completed Oven" you will see that there is no door.  Obviously when baking bread there is a fitted thick door that is first soaked in water for about an hour before firing so that when the coals are scraped out and the floor is cleaned, the door is placed in to balance the heat between the walls and the floor before putting in the bread.  A Raytek lazer thermometer gives me the temperature of the floor and walls before placing in the bread.  As for pizza, the door is left off with a small fire burning in the oven once it reaches the desired temperature.

ClimbHi's picture
ClimbHi

TParr,


I'm not sure what you're saying exactly. You say "there is no door", but then you indicate you use a water-soaked door when baking. I assume you meant that there is no door permanently fixed to the oven, e.g., on hinges. This is typical -- WFO doors are usually designed to be put in place only when needed.


BTW, you can skip the soaking if you construct a heat-resistant door:


http://www.thefreshloaf.com/node/21892/oven-door


I can use this door even with a small fire burning, as when I'm smoking something lik a turkey.


ClimbHi
Pittsburgh, PA

Pop N Fresh's picture
Pop N Fresh

ALL WELL WORTH IT!.....I spent four very hot, back-breaking months last summer building the cob oven seen in the links below.


http://www.flickr.com/photos/54008569@N03/sets/72157624846466835/show/


http://www.flickr.com/photos/54008569@N03/sets/72157625272091784/show/


http://www.flickr.com/photos/54008569@N03/sets/72157625247426500/show/


The oven's chimney is not type "Class A"... I was being a little frugal.  As you can see in the images I still need to extend it up and out the back-side of the roof.  If you go through the roof, the chimney must be Classs A.


Some smoke does still come out of the front.  And as you can see I also get soot on the front.  The pipe is only 6".  In hine-sight, I should have gone much larger... in other words... with a nine square-foot interior, I would have been better off with even a 10" Pipe. 


Be sure to install a damper in the pipe just above the oven.  This way, when you go to clean-out the oven in preparation to baking, you can close it and retain more heat.


Also in hine-sight, I should have put the chimney outside the oven chamber!  This way you loose less heat and only create up-draft, as well as, evacuate the inevitable smoke. 


My eyes might not be 20/20... but you can always count on Hine-sight being 20/20!


I still get some smoke coming out the front and soot build-up.  I just wash and paint as needed to keep-up appearances.


As far as heat loss... Build it right the first time!  I have about 7" insulation on the very bottom of the sub-floor.  Above that I have 7" crushed stone (Thermal Mass).  It would have been nice to lay the fire-brick on their side (could have been 4.5" thermal mass, instead of the 2.5" that I settled with to be frugal...)


In some areas, the total thickness (all layers) of the walls are as much as 30".


This past fall, with a six hour burn, clean-out and then a one hour evening rest period.  I get about two hours bread baking, a few hour roasting & casserole cooking.  Then cookies and/or cakes.  And finally I do all of my low and slow over-night (10 to 12 hours) at temps of about 325f that night.  In the morning the oven is still about 200f.  The Boston Baked Beans are amazing!  And the Short Ribs...Mmm, Mmm, Mmm!


Let me know if I can help in any other way.


Robert