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.

[daidensacha]

Curing fires started

Yesterday I managed to get the flue finished, through the roof and sealed.

I was like a kid at Xmas, so excited to get the first fire going inside the oven.

Turns out, it works!! So beautiful, watching the fire. The vent and flue works perfectly, No smoke comes out the front of the arch, as the flue is like a vacuum. From the beginning even before it warmed up. I checked the flue after 6 hours and on the outside it was totally cold, albeit the fire was not pumping hot, so Iooking forward to checking it when I cook pizza on Thursday.



We had snow the last days, and its getting too cold to even consider finishing the render now. But its covered, and protected from the weather so I‘m happy. This week it might be ok, as we will have a 3 day window of maximum temps around 8 degrees. I‘m considering finishing rendering the front face of the chimney so I can mount the light and remove the tape around the bricks.

[UtahBeehiver]

Congrats, now the food cooking fun starts. Check out Karangi Dude's cooking thread, he goes way beyond cooking pizzas taking WFO cooking to an art.

[daidensacha]

Stainless steel double walled flue

I thought I would just add some photos of the stainless steel flue.

Actually, it was something I worked out early in the planning process, as I really wanted to to ensure that smoke exited the oven via the vent, and not the front of the arch. Started with working out what size flue, which was 200mm in my case, and then calculating what size vent was sufficient to match the flue. With david s input and guidance, I made a vent gallery out of castable refractory that would sit on top of the arch. (see following post for some images). Then 2 x 300mm x Ø200mm Scahmott flue to sit on the vent. I bricked put around the schamott flue, and then bolted a stainless steel base plate to the chimney, with a single to double walled flue adapter. The 1.5 meter of stainless steel flue then on top though the roof.

Its amazing to watch the flow of air in the oven, created by the cool inflow through the front of the arch, and the warm outflow of smoke filling the dome though the top of the arch and straight up the flue. It creates at times a mini tornado in the vent gallery, which I see from the swirling smoke and ash, which then swishes up the flue. It’s really efficient, with almost no smoke passing the vent opening and coming out the front of the arch.

[daidensacha]

Castable vent

This was actually the first thing I did when starting on the oven, end of last winter before I could get started on the oven as it was still too cold. david s very kindly shared his knowledge of working with vermicrete to make moulds, and casting with castable refractory.

Photo 1. I had my Schamott flue size, ID Ø200, OD Ø240mm, and from that calculated a vent opening size that equaled the ID of the schamotte flue, 377mm x 126mm. I My goal was to create a mould that would transition from the rectangular vent opening to the circular flue opening with smooth curves so to facilitate unimpeded flow of smoke through the vent and into the flue. The mould was made from 5:1 vermicrete so I could easily remove it from the cast once I had poured the castable refractory. Easy to carve.

Photo 2. I created a form in which I could place and center the mould, and easily remove once the castable refractory was set. I allowed for 50mm thick walls.

Photo 3. The castable refractory set really well, and it was easy to scoop out the vermicerete, leaving the inner of the vent with smooth walls and curves. I bought a schamott adapter plate and made the vent gallery so the adapter plate would nest in the top. It was a perfect fit.

Photo 4. On top of the arch, I then set up some forms to cast a base on which the vent gallery would sit. I used castable refractory again as I had left over from casting the vent. I then used heat proof mortar when placing the vent on the base.

Photo 5. It became a solid base for the flue once the vent was on top of the arch, and the adapter place was mortared to the vent gallery.




No one will ever see it, or fully appreciate the work and planning that went into it, but I will know it is there inside the chimney, and watching the whirlwind of smoke as it flows out of the dome and directly up the vent and flue gives me satisfaction.

[daidensacha]

Congrats, now the food cooking fun starts. Check out Karangi Dude's cooking thread, he goes way beyond cooking pizzas taking WFO cooking to an art.

Hey Thanks Russel. So much to look forward to, and I’m so enjoying getting started on the cooking. Had my second curing fire today, and was thinking of you when I checked the vent I placed on top of the dome. A lot of moisture was coming out which was good to see.

I’ll be starting with pizza, and have a pizza birthday party planned for 23 December. Then on the 24th I want to cook the Xmas goose in the oven. Last year on on the grill rotisserie, but this year in the pizza oven. I will definitely check out Karangi Dude’s cooking thread, thanks for that tip.

[Giovanni Rossi]

daidensacha Been following you since the beginning. Nice work! The payoff is near!!

One thing you may want to consider is a band of hardware cloth under the flue cap as a spark arrestor and to keep out critters.

[daidensacha]

daidensacha Been following you since the beginning. Nice work! The payoff is near!!

One thing you may want to consider is a band of hardware cloth under the flue cap as a spark arrestor and to keep out critters.

I was wondering how long before someone noticed that with my flue. 10/10 Giovanni

I’ve been on to the manufacturer to ask them if they can make one up for it. Failing that, I already have a perfect piece of stainless steel sitting in my Amazon shopping cart ready to buy if needed. Just means I need to take it to the engineering shop to put it through the rollers and tack weld it, which I can do, but at this point would happily just buy one that fits from the manufacturer.

I was entranced yesterday watching the mini tornado at the vent opening created from the meeting of the cool inflow and warm outflow of air though the oven arch. Normally invisible to the eye, but with smoke and ash very visible and fascinating to watch. I did stress over whether the flue would work as I wanted it to, and after all the work, it’s outperforming my expectations.

[Giovanni Rossi]

I used a Duratech flue. They offered a mesh ring arrestor for $30 USD

I could get a small roll of hardware cloth locally for ~ $10 and had a lot left over for other uses. But, I had some remnants form past projects, so cost $0

I know what you mean about "flue anxiety" (could this be a defined FB Forum disorder? ), i used 6' and really didn't want to spend for another section of stainless.

The other mesmerizing view I like is the flame and smoke swirl from a fire at the side of the oven looping along the top of the dome then downward toward the floor and across the top of a pizza !!!

[daidensacha]

Giovanni Rossi The manufacturer replied and said if I bring the flue cover in he will put a spark arrester around it. Easy peasy. That’s my first job in the morning.

Bonus, we have 3 days of 10-11C, some I’m making the most of it and doing the final coat of render on the chimney. I wasn’t expecting it to be warm enough until next spring. It’s a blessing.

The curing fires are a super introduction to getting to know the oven. Each day it heats faster, and retains more heat. I’ve been putting wood inside at the sides of the dome. When I put them on the coals the ignite real quick. Today there was a 30cm round totally clear spot in the centre of the top of the dome above the coals.

I put the insulated door on this afternoon and closing the opening totally. I want to measure the inner temp tomorrow when I open it to start the next fire. Also curious to see how the door handles the heat.