2024 Neapolitan oven build

[daidensacha]

Thermometer Installation

I wonder if someone has experience and knows how to install a probe thermometer as in the following image?



I’m designing a door, which is where I want to install it, simply to monitor the internal temp in the days following heating it to cook pizza.



This is a screenshot of the sketchup plan I’ve been working on. It will be filled with left over calcium silicate insulation that was used under the floor. It will be 100 mm thick, with a 3mm stainless steel front. The sides and back will be 1.5 - 2 mm stainless steel sheet.

What I don’t know, and documentation doesn’t make clear, is how and where the thermometer probe should be placed. Should it protrude through the inside of the door and be exposed, or can it be placed under the inner stainless steel face?

Appreciate any input.

[Toiletman]

Just wanted to add some compliments on your progress and build quality once again: looking great! I'm slightly jealous that you made such progress while I have closed for the season (and was enjoying the beach).

A couple of notes on insulation thickness:
- it's actually not true that 'there's no such thing as too much insulation': for pipes or spheres, by adding insulation you also increase the surface area of the thing that you are insulating: there is a maximum after which adding more insulation actually makes performance worse, as the increase in surface area is more significant than the decrease of heat transfer due to insulation. However, this maximum is far away from realistic sizes for ovens, so you are indeed making the heat loss smaller with your large thickness of insulation (see attached graph, based on my oven dimensions).

Thermometer Installation

I wonder if someone has experience and knows how to install a probe thermometer as in the following image?

What I don’t know, and documentation doesn’t make clear, is how and where the thermometer probe should be placed. Should it protrude through the inside of the door and be exposed, or can it be placed under the inner stainless steel face?

Appreciate any input.

Did you already ask the the manufacturer/seller? Do you know what the working mechanism is?

I have no experience with something that looks like your picture, so below is more generic/speculative info:

Thermocouples/thermistors typically have a very small sensor very close to the tip of the probe, so these could be mounted perpendicularly to the face of the door, with the tip sticking into the oven, or just flush with the SS wall in a little hole. However, these typically come with a display and a power supply instead of a clock.

If the working mechanism depends on expansion of a gas or liquid, or deformation of bimetallic spring or sth like that I would imagine that the full tube has to be immersed in the heat, so then it should be mounted in parallel to the wall. Mounting it behind the SS will result in a small temperature difference vs the actual air temperature in the oven, but as the sensor will be sandwiched between insulation and the stainless steel might not be very large. (assuming you are interested in 10-20C accuracy, not in single digit).
Does the manufacturer specify what the material of the line attached to the probe is and if it's supposed to be exposed to the high temperatures as well? If so you could mount the probe on the 'inside' of the oven, to the back of the door, guiding the wire through the insulation.
It might be that the probe has been designed to be embedded into a firebrick, with the thermal mass surrounding the probe and thereby also giving a more accurate reading of the actual temperature of the mass of the oven, instead of for instance the radiative heat received by the probe or the SS wall of your door. If this is the case you might consider adding a brick with a hole in it on the back of your door, or partially embedded into the insulation. Or you could reconsider the location completely and mount it in the oven instead of in the door.

[daidensacha]

Toiletman Good points about how the thermostat functions. I hadn’t considered that, and now I’m curious. The tube that runs from the thermostat to the probe is can be bent to shape, like its copper at a guess. Quite long, over a meter. But I don’t want to run that into the oven chamber.

I wrote to the vendor I bought it from on Amazon and they wrote back that they have asked the manufacturer for installation information. They will let me know as soon as they get that, and I’ll share it.

The weather here is turning cold, and i’m tackling tasks now one at a time as each depends on the completion of the previous. My roof sheets are due to be delivered on Tuesday, so Wednesday I’ll get those up, and hopefully complete it same day.

Then I need to put a flue extension up through the roof, and seal it, which has its own complication as the Sandwich panels are not flat on top. But hoping to have that completed by weeks end, depending on whether I can source my flue materials this week. Going to a local factory this morning to see if I can get a deal on the parts I need directly from them.

Then I need to do my drying fires, which will take a week or so. Following that, depending on temperature I’ll do my final render. I’ll need luck with a few warmer days for this to happen this year, so keeping my fingers crossed. But it’s looking like I’ll be having pre xmas pizza and glühwein, yay.

Where I live is a small village, and I’m the crazy Australian building a pizza oven that every one here is totally impressed with, but can’t understand why. We will have a village pizza party.

[david s]

[QUOTE

A couple of notes on insulation thickness:
- it's actually not true that 'there's no such thing as too much insulation':

[/QUOTE]

While the chart illustrates the reducing effectiveness of increased insulation because the graph is not a straight line, the issue is compounded by the massive increase of area required for each subsequent layer of blanket, This means that costs go up far higher than the reducing amount of gain via heat loss.


Mountng it in the door leaves it more vulnerable to damage.I think a sheath is advisable for all probes. Nearly all temperature measuring devices, particularly electronic ones, stuff up sooner or later. Most oven owners get to know their oven characteristics, time taken to get to temperature etc. and rely less and less on measuring devices.Here are a few:

1. A fist held in the oven centre and counting how long you can hold it there.
2. A hand held to the outside of the oven
3.The degree to which the carbon has burned away inside the oven
4. The intensity of of the radiant heat felt with an open hand at the entry
5. If cooking pizzas the visuals and time taken to reach that point are all you need.

When the oven consistently does the same thing every time you fire it, you begin to use these methods far more than any other measuring devices.

I'm interested in the chart you posted. Whilst all insulating materials would show similar heat loss vs thickness results, what specific insulating material and its thermal conductivity was that test conducted on?

[daidensacha]

david s My first job many years ago was working in a pizza bar in Kalamunda, Perth. 2 years, albeit with an electric oven, there is no substitute for experience. Indeed, reading the oven became second nature, and for that reason I wasn‘t to interested in placing a thermometer in the dome, or inside the oven.

I thought the door, if it was practical would be the way to go, but only to get a read on the oven chamber temp each day following the fire to gauge what to cook if I want to use it to cook bread, meat, or cake, or other stuff.

I did a simple test with this thermometer putting it in boiling water. Next step was testing in in/on my gas BBQ. My BBQ is a beauty, can get it up to 300C, so I wanted to test the efficiency of the thermometer I have against the stainless steel top when its hot, as oppose to being exposed inside the BBQ chamber.

Could be worth getting a different type of Thermometer as you describe with a sheath going through the door. Then I can remove the thermometer to replace if it’s ever needed.

I can also just revert to using my infa-red thermometer gun, and get to know my oven. Might just be the best in the end.

[rsandler]

FWIW, in my first oven I had a probe through the door (it was a long-stemmed deep frying thermometer stuck through a small hole, nothing fancy); it is just as well that it was removable because the probe did fail after several years. On oven #2 I left off the thermometer to start with, thinking I could always add one later, and haven't missed it particularly. Certainly haven't felt compelled to make a hole for a new thermometer. Your mileage may vary--I do have the experience of having a wood fired oven for 10+ years, though my oven #2 performs very differently from oven #1. But if you make your door reasonably moveable, I find it's always easy enough to just open up and shoot it with the IR thermometer.

[daidensacha]

Door Design and considerations

rsandler Thanks for your input.

I’m questioning whether I will add the thermometer or not now. Add it in the door means cutting holes for it, that at a later stage I might regret. When I‘m n it clear on something, my ideas start as seeds and evolve as I become clearer and more informed. I‘m not attached to adding the thermometer, and remaining flexible as to if, or where I might add it if I choose to proceed with that.

I‘m still researching and informing myself with my door design.

I would like to use stainless steel to make the shell. I have a piece of 10 cm thick calcium silicate insulation left over from what I used under my floor.

Stainless steel shell
Trying to use minimal thicknesses so the door stands up to its life, I thought 1.5 - 2mm thick on the sides, back and bottom (2.92kg), with 3mm thick front (2.82kg). Estimated total 5.74 kg only for the stainless shell.

Calcium Silicate fill
The Calcium silicate weighs in at around 5 kg, and then I would have handles to consider. That would make my door around 11-12 kg in total, solid but hefty.

Ceramic Fibre fill
As an alternative fill, I could also use Ceramic fibre blanket, much lighter at approx 1.8 kg to fill the shell. The door in total would come in then around 8 kg, and 3-4 kg lighter than if I were to use the Calcium silicate.

The Ceramic Fibre blanket is 128KG/m³, with rated max temp of 1260C (vs Calcium silicate 1000C). Theoretically Ceramic fibre is lighter, and withstands higher temps.

I‘m all for lighter given I will be sliding the door in and out more than others. What would be good to know before deciding, if someone knows, is the performance difference between the two types of insulation. Using 10 cm fill in the door, how likely is it that the outside of the door will get hot? I know the heat will conduct along the sides, but here I‘m more interested in what heat will get though that insulation.

[nlinva]

I'm also at the making-a-door stage, so have been thinking about some of these same issues.

My guess would be that most heat reaching the outside of the door will get there through the conduction of the steel sides, so the specific type of insulation inside would not matter as much.

One possible advantage I have considered of the CalSil is that, being rigid, it will help the door keep its shape, against possible warping tendencies under high heat (though it sounds like you'll be using thick enough steel that that would not matter).

Also, since we want there to be some space on the sides and top to prevent the door from getting stuck upon expansion/shrinking, there will always be a route for heat that bypasses most of the thickness of the insulation (basically a short diagonal from the inside of the oven through the inside corner of the door to the air channel on the side). How much this will matter I'm not sure, but it makes me wonder about whether thicker insulation really matters a lot (i.e. does 4" make a big difference compared to 2"?).

[daidensacha]

I'm also at the making-a-door stage, so have been thinking about some of these same issues.

My guess would be that most heat reaching the outside of the door will get there through the conduction of the steel sides, so the specific type of insulation inside would not matter as much.

One possible advantage I have considered of the CalSil is that, being rigid, it will help the door keep its shape, against possible warping tendencies under high heat (though it sounds like you'll be using thick enough steel that that would not matter).

Also, since we want there to be some space on the sides and top to prevent the door from getting stuck upon expansion/shrinking, there will always be a route for heat that bypasses most of the thickness of the insulation (basically a short diagonal from the inside of the oven through the inside corner of the door to the air channel on the side). How much this will matter I'm not sure, but it makes me wonder about whether thicker insulation really matters a lot (i.e. does 4" make a big difference compared to 2"?).

I was just working on a spreadsheet to compare the price and weight of stainless steel vs aluminium.

For my door material, pieces ordered cut to size.

Material	Weight (kg)	Price (Euro)
Stainless steel	8.02	153.56
Aluminium	4.15	84.19
Ceramic Fibre	1.8	20.00

Stainless steel door would be 9.82 kg, vs Aluminium 5.95 kg. Nearly 4 kg difference.

With the Alu, the price is for 2.5 mm sides, top and inside, with 4 mm outside. Even with ceramic fibre I think it will be solid enough, as long as it‘s not being thrown around.

I‘m sure I can save a little on price by shopping around, but its a big saving to go with Aluminium.

I allowed for 5 mm gap on the sides and on top of the door to allow for expansion. Aluminium is a better conductor than stainless steel, and will heat up faster. Having thicker insulation by my reasoning has two advantages. 1. Less heat lost through the insulation from inside to outside the door. and 2. The sides being longer mean its further for heat to move through conduction.

The bricks on the sides of the door are thermal mass, so being heated, any heat on the sides of the doors will not be lost to the bricks as long as they are hot.