2024 Neapolitan oven build

[daidensacha]

Stainless is highly conductive and therefore a drawback for a door which you want to be insulating. Not as conductive as mild steel or aluminium but still orders of magnitude more conductive than insulating materials. Insulation values are calculated by using the reciprocal of thermal conductivity . The higher the conductivity the lower the insulation value. Use this same figure to compare the thermal conductivity of rockwool against that of ceramic fibre blanket. It will be quoted in the data sheet of the product you’re researching. Unfortunately it’s further complicated because thermal conductivity varies as the temperature rises for any given material, so the TC at 200C should also be considered.
I’ve been through this and it’s a bit complex, because all the products vary somewhat. The blanket usually comes in two different densities as well, the higher density is marginally less insulating. Rockwool does not cut as neatly as CFB and has a slightly lower temperature resistance. But as you’ve pointed out, is miles higher than the service temperature you’ll be exposing it to. The rockwool is slightly poorer as an insulator but I found this was offset by its cheaper price. I only used it for two ovens because the CFB cuts so beautifully it’s way easier to fit.

Getting back to the stainless, you don’t say how thick it is. Obviously the thinner the material the less weight it will be, but the more thermal mass you’ll be adding. Thin stainless has the annoying quality of warping which may interfere with the door not sealing properly, which will lead to rapid cooling of the oven. The warping is reduced by making the stainless thicker. Because the door receives uneven heat by radiation it gets a lot hotter in the centre as the perimeter is shielded by the rebate in the oven mouth. This is likely to compound any warping issues.

I did consider warping when deciding on the thickness. I also spoke with the boss at the engineering workshop and he said stainless was a better option over aluminium which I was considering to reduce weight. Weighing up the pros and cons, I settled on 1.5 mm sheet for the inner and sides, with 3mm for the front. I have 25 x 2mm strips welded around the sides of front, so they slot inside the back and will hold the screws. I‘ll be interested to see how much it warps, but it seems quite stable and solid.

I‘m only weighing up using the Rockwool as a fill for the door. But I might use it on top of the perlite in the chimney as the last layer under the base plate that will sit on top. Given I plan to put the flue up tomorrow, and i have Rockwool on hand now, out of necessity it might get used. Then I‘ll put ceramic fibre in the door when it arrives. I wanted this done before I start the fires so I can use the door over night to preserve heat throughout the week of fires. I think it will help with expelling water. It’s getting cold now, with our first snow yesterday, and -3C, getting cool to so want to keep the oven warm. I‘ll check out the TC of each product to compare them.

[david s]

1.5mm should be enough to prevent warping at baking and roasting temps, but not sure how it will cope if placed in the mouth at pizza temperature in an effort to retain maximum heat overnight for follow up cooking the next morning.
My door, with a timber outer facing doesn’t cope if placed above 300C, which is higher than roasting or baking temperatures anyhow.
If you can hold your hand against the outer face, then you’re doing ok.

[daidensacha]

1.5mm should be enough to prevent warping at baking and roasting temps, but not sure how it will cope if placed in the mouth at pizza temperature in an effort to retain maximum heat overnight for follow up cooking the next morning.
My door, with a timber outer facing doesn’t cope if placed above 300C, which is higher than roasting or baking temperatures anyhow.
If you can hold your hand against the outer face, then you’re doing ok.

What happens to your door at 300C? You said it doesn‘t cope, is that with warping, burning, or overheating?

I‘ll post some images of the second steel door, Here is a pick of it being welded. No insulation, 4mm steel plate with 3mm steel cutout welded on the front. Also has steel rollers on the front to make it easier to roll out. I‘ll post more details with weight etc, and images in a few days.



My idea was to use this when baking at high temps. I know it will get hot being steel. It was supposed to be easier to handle than the stainless steel door, but I think its heavier.

[daidensacha]

Steel door with rollers


The steel door I made weighs in at 6.92 kg. I included rollers at the base of the door so I can easily tilt the door to roll it out of the oven opening without having to lift or drag it. I wanted to save damage to the floor putting it in and out over time. My intention is to use it when heating the oven and baking, and to use insulated stainless steel door the days after heating the oven to retain heat. I‘m yet to test both doors, but it will happen soon.



The rollers are steel, Ø 22 mm, with 5 mm hole for the bolt. Tilting the door back makes it really easy to roll the door and the rollers work really well.

4mm inside plate, 3mm outside plate cutout welded from the back and sides. 16mm round steel bar for the handles.

This wouldn‘t have been possible without the help and amazing machinery at Kienberger Engineering, thanks to Richie. Never saw a plasma cutter close up at work before, but impressive.

[david s]

"What happens to your door at 300C? "

Wood begins to self ignite north of 250C. Italian ovens traditionally had wooden doors and when used for cooking bread, some excess dough was used to plug up around the door to seal it. No fancy temperature measuring devices either. Usually a closed fist placed into the oven for as long as one could stand it, was the method. Three seconds was the required correct test. 2 secs = too hot, 4 secs = not hot enough. To reduce charring of the inner face the doors were usually soaked in a bucket of water .Eventually a new door would be made.

Because I like the look of a wooden door and it is traditional, that's what I've settled on, but with a cast insulating panel to take the sting out of the transferred heat. Weight, cost of materials and fabrication time are also part of arriving at my solution. The door weighs 3.7kg allowing one handed operation.
For baking or roasting the door is in place for up to 3 hrs, by which time the temperature has dropped a little and the timber is not vulnerable. Generally roasting or baking is done at temperatures under 300C anyhow. Of course roasting can be done without the door and a live fire on the side as well.

A thicker insulating panel would extend retained heat cooking, but make the door heavier and less manageable. As a further measure to reduce conduction between the insulating panel and the timber face, I stand the two apart by 2mm with high temperature silicone, pic 3.

What can't be done is to place the door at pizza temperatures after a party in the hope of retaining sufficient heat for cooking the next morning. The result is likely to be that shown in the first pic. Despite instruction about this and the clear instruction on the door, a customer who hired my mobile oven forgot (after over consumption of beer no doubt). Because my oven is small with very low fuel consumption, it's very easy to fire it up to quickly restore higher temperature.

[daidensacha]

Stainless steel insulated door

Today I finished drilling the screw holes and tapping the inner fitting 2mm sheet to hold the screws. The 25mm ceramic fibre insulation was delivered so I cut out 4 layers to fill the 100mm depth of the door, and screwed the front and backs together.

Filled with the ceramic fibre insulation and screwed together, it weighs in at 8.77 kg, a little less than I expected. 1.5mm sheet for the inside and sides of the door, with 3mm sheet on the front. I used 2 x 25mm stainless strips welded to the front, that fit inside the back and have holes tapped for the 3 x 16mm screws that fix the front and backs together.

16mm stainless rod for the handles.

I made it so I could disassemble the front and backs just in case at some point in the future I need to change the insulation. Given the ceramic fibre can withstand 1260C, I doubt it will suffer from the heat. I‘m curious to see how the structural integrity stands up to the heat when I‘m using it to retain heat the days after heating the oven. I‘m hoping that the shape of the back with welded corners, screwed to the 3mm front plate will make it strong enough to hold its shape. I‘m also betting that the 10cm depth full of the ceramic fibre is enough to prevent the handles at the front getting hot. I will update when I test in in the next weeks.





Yesterday I drill holes in the top of the chimney bricks, cleaned out the holes, injected anchor adhesive and inserted M8 x 120mm threaded bolts. Today I was able to fill the top of the chimney with rockwool, and mount the single to double wall flue base plate on the chimney. Double checked my drilled hole in the roof that is is centered over the flue, and its perfect. I‘m ready in the next days, weather permitting to cut the hole in the roof and mount the flue on the chimney up through the roof. Just waiting on a flashing to be made so I can water proof the roof when I do it. That will be the final step before having my first fires in the oven. Getting really excited.