Sheet metal oven, brick floor, can't reach 450C degrees. Help?

[branded]

Hi Guys,

I posted this is another sub-forum, not getting much love there, hopefully it get more noticed here.

I bought a cheap portable (I'm renting) wood fired oven made from sheet metal and it is somewhat insulated. I know... I know... I know it's not brick, but I think I should be able to get it to 450C degrees if I modify it.

I have drawn up roughly how it's made here: http://i.imgur.com/48kT9R4.jpg

Basically is a half barrel sheet metal oven with insulation between the sheet metal. I believe it's fully insulated in the roof/sides, back and on the door. On the floor, it came with fire bricks on top of an uninsulated sheet metal floor, so there's only fire bricks on the floor - nowhere else, the rest is sheet metal. I bought 25mm of calcium silicate and laid that between the fire bricks and sheet metal floor - so it should now be insulated everywhere. But I'm still struggling to get it to 450C, I get maybe 350C, maybe more if I go crazy with wood, but If you look at the oven plan image I provided, I'm putting enough wood to cover eight bricks and as high as the roof.

Is it because the dome is not brick? I know it may be a dumb question, just asking. What do you think I could do? I really thought this would have potential if I modify it.

Thanks!

[david s]

Re: Sheet metal oven, brick floor, can't reach 450C degrees. Help?

First up, if the sheet metal is normal steel rather than stainless, expect problems with corrosion. The heat and moisture that condense inside it will accelerate rusting. Difficulty refacing higher temps is probably due to a combination of not enough insulation and the low thermal mass in your oven. Perhaps you'll have to get used to cooking pizzas in 5 mins rather than two.

[branded]

Re: Sheet metal oven, brick floor, can't reach 450C degrees. Help?

Thanks for your response, David. I appreciate it.


Firstly, I don't mind if it only lasts a year or two. It's just a temporary oven before I buy a house in the next 6 months. Secondly, the metal is actually "stainless" covered by vitreous enamel and it's covered, so hopefully it'll last until then.

It's this oven here (hopefully I'm not breaking any rules by posting this): http://www.bunnings.com.au/jumbuck-s...oven-_p3170978

When you say "thermal mass", "in English", do you mean fire bricks or refractory material? How could I modify it to add thermal mass?

Regarding insulation, when I've had it at it hottest (I think about 380C), I could still touch the sides/roof with my hand.

Any tips on what I could do to solve this issue?


Thanks!

[david s]

Re: Sheet metal oven, brick floor, can't reach 450C degrees. Help?

Thermal mass is any heavy material that will store heat (usually fire brick or castable refractory which have quite high mass but release their heat fairly slowly). As soon as your flame dies a little then the thin steel (high thermal conductivity) will begin to cool. I think you've done the right thing by insulating under the floor. If you can hold your hand on the top of the oven then it must be fairly well insulated. When cooking 2 min pizzas you need to maintain a flame on the side to keep the temp up, this would apply more so with your oven because of its low thermal mass. Adding thermal mass to the top of the oven would necessitate removal of the outer casing and insulation, then adding the thermal mass, replacing the insulation, plus a little more because the diameter will now be a little bigger and creating a new, larger outer casing. Probably not worth the trouble. Try maintaining a bigger fire while cooking your pizzas first.

By the way, how thick are those floor bricks?

[mrchipster]

Re: Sheet metal oven, brick floor, can't reach 450C degrees. Help?

A few ideas on heat. If your drawings are to scale your floor bricks are very thin. You may want to get some refractory brick to add another layer to your floor. Most here on this site are 2.5 inches thick.

Use only very dry wood cut to wrist size pieces. Do not pile on heaps of wood but build a medium size fire in the center of the oven and then move it to the side once oven is warm keep adding wood one or two sticks at a time to keep a nice flame licking over the dome.

Cook your pizza on the side of the oven opposite the fire. This will allow you to see how done the crust is getting and turn it before burning.

Your oven will never be able to retain much heat because of the stainless top but you should be able to produce some nice pizza with a thicker floor and a good live fire.

If you cannot find firebrick you may be able to get a piece of remnant soapstone from a cabinetmaker or kitchen remodeler in your area. The cutout scrap removed for a sink would work great in your oven to add some thermal mass to the floor and would give you a great cooking surface.

If you want to go real cheap put cob (clay/straw/water) mix between your floor tile and the insulation board you installed. It will take several low and slow firings to dry out the cob but it will give you some very cheap thermal mass. I would apply the cob let it dry for several days, dry it with low slow fires several firings and then put in the floor tiles leveled over a thin layer of sand or fireclay. The cob will be a little uneven so the sand/fireclay will allow you to get the floor perfectly level.

Do not use anything other than soapstone, cob or refractory brick for thermal mass. Nothing else will hold up.

[david s]

Re: Sheet metal oven, brick floor, can't reach 450C degrees. Help?

Do not use anything other than soapstone, cob or refractory brick for thermal mass. Nothing else will hold up.

You should add castable refractory to this list Chip. In fact it would probably be the best material to use because there would be no cutting required.
Don't go any thicker than a total floor thickness of 2" or it's likely to be counterproductive.

[Wiley]

Re: Sheet metal oven, brick floor, can't reach 450C degrees. Help?

Sorry but I can't work up much love for this oven. Besides all that has been mentioned, one of the biggest drawbacks/shortcomings of this WFO is the fact the chimney vents straight out the top.

So even if one adds refractory mass, heating this oven will be inefficient. There is little thermal mass in the arched roof and little in the hearth. As we know it's more difficult to heat the hearth than the dome and in this WFO the hearth is the principle heat reservoir.

Sorry,
Wiley

[mrchipster]

Re: Sheet metal oven, brick floor, can't reach 450C degrees. Help?

You should add castable refractory to this list Chip. In fact it would probably be the best material to use because there would be no cutting required.
Don't go any thicker than a total floor thickness of 2" or it's likely to be counterproductive.

David, great point about the castable, I have not worked with it so it rarely comes to mind.

I think tossing any significant cash into this "oven" would be better spent on your next proper oven.

Wiley, As to your comment "As we know it's more difficult to heat the hearth than the dome and in this WFO the hearth is the principle heat reservoir. " that is why I mentioned soapstone. It does a great job of absorbing and releasing heat. And may help in getting a nice crust on your pizza.

[deejayoh]

Re: Sheet metal oven, brick floor, can't reach 450C degrees. Help?

Do we have some Celsius/Fahrenheit confusion on this thread?

450c is 842F. You're not going to get Neapolitan pizza performance out of a barrel oven with no insulation. 350C sounds about right. Maybe you can get it up to 375C. But i wouldn't throw money at it expecting too much. I think most posts I read suggest that people cook pizza at around that temp even in brick domes.

[branded]

Re: Sheet metal oven, brick floor, can't reach 450C degrees. Help?

Thanks for all your help guys, especially mrchipster. I used wrist-sized bits of wood and I purchased this and used it as a thicker pizza stone to add to the bricks below it...

... and well... I posted my results. I'm pretty pleased so far.

See here for the results:

http://www.fornobravo.com/forum/f25/...rly-21706.html

[mrchipster]

Re: Sheet metal oven, brick floor, can't reach 450C degrees. Help?

The pizza looks great. What did you decide to add to the oven as a thicker pizza stone?

You just said you used "this" it lsounds like you thought you added a photo of something.

[branded]

Re: Sheet metal oven, brick floor, can't reach 450C degrees. Help?

The pizza looks great. What did you decide to add to the oven as a thicker pizza stone?

You just said you used "this" it lsounds like you thought you added a photo of something.

Ah yes, I forgot the link:

Kamado Joe Ceramic Grills | Classic Heat Deflector

I don't own a Kamado Joe, I just saw it at a BBQ shop and thought it would be good to place at the back of the oven since they are semi circle. But then I just decided to use them as a pizza stone for more heat on the bottom which is where more heat is needed. I remember my last pizza was better cooked on top than underneath. The only problem I have now is that after baking one pizza, I have to wait maybe 5-10 min until I put another one in there so the bottom heats up again. I will be buying much thicker bricks for the bottom and then using the Kamado Joe stone for the back.