Heat conduction among other thing

[Chewycrust]

Hi all,

A bit of context...

I'm based in the uk. Have been making pizza and breads enthusiastically using an indoor electric fan oven and pizza stone for quite a while now. Having just bought a house and planning a garden refurb, I'm considering a self build wood fired oven. We have a large ish garden, few close neighbours despite being in a very busy part of manchester.

Local regulations allow for an outdoor oven as long as it doesn't have a roof as that would count as a fireplace and would have to be smokeless!

I've had a good look through the forums but my apologies if any of this has already been covered.

I know with a wood fired oven high heat and a long retention of that Heat are often prime concerns, I have a few things I'm unsure about relating to this...

As I understand it, a high heat is desirable for creating traditional thin crisp pizzas inonly a couple of minutes, this heat is created by a large thermal mass (thick walls, good amount of thermal mass for storing heat and a good refractive outer shell?) this also means a long time to get up to temperature and a long cool down period. Am I at least close so far?

As I'm quite happy with the results of my indoor oven running at 230-250 degrees (I favour a New York crust) and my reasons for outdoor oven are more about outdoor living, sociable cooking and a smokey flavour, would it be sensible to have less than maximum thermal mass to allow a quicker warm up and less fuel required?

I'm intending to build a small ish oven based around some of the oil drum designs I've seen on the forum. Essentially a half oil drum on a stand with firebrick oven bottom and conventional brick arch over the top.

I intend to cook pizza, bread and roast meats along with some other things... Jamie Oliver has a lot to as wer for in our house!

In order to cook bread and roast meats will it be necessary to have some sort of door and mechanism to close the flue to retain heat?

I'm also condidering placement in the garden. I suppose it goes without saying that no trees can be directly above the chimney, how far away from trees should I have the walls of the oven? How much heat would I expect radiating through the bricks? One of the ideal locations for the oven would be right up against a wall of the house but I don't want to give myself any issues with heat conducting into the house walls and cracking bricks or mortar?

Any thoughts or advice gratefully appreciated.

Thanks in advance.

Tom

[Slowly but Maybe]

Re: Heat conduction among other thing

I'm surprised that nobody has responded to this. My own personal opinion is that you should not skimp on building materials. Use proper firebrick and insulate it well. Be sure to put fiberboard insulation underneath the floor bricks. Build an insulated door to use with it. I have a 36" Pompeii-style oven that I built using FB plans. Last time I fired it up, it took less than two hours to get it up to 900deg+Farenheit. It used a bit of wood, but by no means did it require a lot to get it to that temp. No more than you would burn in a fire pit while sitting around having a few pints. After cooking the pizzas that night, I closed the door on it and went to bed. Next morning (10 hours later), oven floor was at 525degF and dome temp was at 600degF. There was no fire, I hadn't added any more wood, that was just heat that had been retained in the bricks due to the oven being properly made and insulated (and closed off with insulated door). Had I chosen to, I could have cooked bread all afternoon in that thing. Sunday morning, 36 hours after having fired the oven the first time, the temps on the oven floor were still around 250degF, perfect temp for slow cooking meats. All of this was from the one firing on Friday evening, so to say that ovens with lots of insulation and thermal mass require a lot of fuel is really not quite accurate, when you consider how long that heat is retained after the fire has burned out completely. Don't skimp and use regular brick. You will end up using far more firewood that way.

[oblertone]

Re: Heat conduction among other thing

Tom, hello from Devon; the design of your oven really depends on what you want to use it for ? Pizza is of course a 'given' but you want to cook bread, roast joints & bake desserts, it all depends when and for how long you want to do these other things. For example my oven is made from recycled building bricks for the dome, storage heater blocks for the floor and a modicum of insulation under & over; it also has an insulated but not tight fitting door*.

The morning after a pizza burn my oven is hot enough to cook a couple of batches of bread, then roast a joint for dinner, but that's about it. I could of course refire and prolong the operation but haven't had the need to yet.

Some of the magnificent builds on here will cook bread for days after a single heat cycle, but they tend to be the fully enclosed jobs with numerous layers of insulation; if that's what you want then crack on. If not, try looking at the igloo builds (like mine) which are more than adequate for most people.

Your oil drum design will work especially if you use blanket insulation over the top; however a thin metal skin won't retain much heat so you'll have to keep a fire going whilst baking which can be tricky. Perversely if you used the drum as a former to build a brick oven and insulated over the bricks then you'd end up with an oven capable of extended cooking. You will need a door of some sort (see *) but these are as varied as ovens !

As to transferred heat, my dome gets to about 40c externally when the interior is at 500c+ and fully 'soaked', I think that's acceptable given the limitations of my build; regardless it is not going to harm the structure of your property even close up. Many fully insulated ovens remain at ambient temperature externally.

For a more UK centric view of WFO's try a little googling and you'll find a similar resource to this board which I hesitate to name for fear of upsetting the Goderators on here

* A close fitting door between the fire and flue will effectively kill the fire and are normally used when the oven is heat saturated; a looser fitting door will allow sufficient air to keep the fire going albeit at a much reduced rate which keeps my oven hot until the morning

Hope this helps, Paul

[cobblerdave]

Re: Heat conduction among other thing

G'day
As a for Forno Bravo member you can get a pdf copy of the FB plans. It's a great resource not just a oven plan. It will explain how the why's and wherefores and make your research a lot quicker.
As Paul has said there is a UK wood fired oven forum goggled that and you'll find it.
Wood smoke. A Dry oven using Seasoned dry wood will not produce much visible smoke except a small amount at start up. You can still smell smoke without the billowing clouds of white which can upset the neighbours.
Regards dave