Excited or Dissapointed - My Cool New Oven isn't Heating Up

[Oven_Man]

Hi Everyone

In another post, I mentioned a Stainless Steel Oven that I was in the process of Building. Finally the oven was completed at my fabricator and boy was I excited. Then the excitement turned to disappointment yesterday when I fired it up for the first time. The oven is heating up quite well and you can feel the blazing inferno of the fire as can be seen in the video.

The problem I have is my Firebricks just can't get up to temperature. First I couldn't get it beyond 450f then I moved my fire around and managed to get it up to 575f with lots and lots of wood and a blazing inferno but that would drop quickly right after baking a pie - the temp would go right down to 380f. The outside of my oven gets hot to the touch such that placing your hand on the outer for more than 3 seconds could probably burn you - I tried to take a temperature reading but because the Stainless Steel has a mirror finish, the IR Thermometer bounced right of the mirror onto the closest object. I would estimate that the outside reaches around 250f.

Quick Summary of my Build
Oven is full stainless steel with an inner and outer dome (Ooni Pro Design but larger 70 X 70 Internal Area)
100mm Ceramic Fiber Blanket between the domes
75mm Ceramic Fiber Blanket at the Back of the oven
75mm Ceramic Fiber Blanket underneath the floor
The right ride of the oven has the firebrick enough to bake 2 X 30cm pizzas - exact dimension is 345mm X 690mm
Left side of the oven has a Stainless steel tray to hold the logs and acts as an ash tray as well
Inner dome height is just over 13"
Oven opening is 18" wide and 8.5" height
Firebrick is 25mm thick 35% alumina medium duty

Looking at the video ,https://youtu.be/T_ZGRyBOzE8 you will notice the flames from my fire doesn't lap around the dome and I know that might pose some issues - I'm not sure why this is the case and still trying to find out.


I'm desperately looking for some suggestions how to circumvent these problems I am experiencing?

Please help

Take Care
Om

[Oven_Man]

I lit the oven now and loaded it with some old wood that was lying around the house which I was meaning to get rid of - what a perfect opportunity to create an inferno.
I also had some old paperwork which I need to get rid of so I threw that in too. The oven is ultra hot - you can barely stand in front of the entrance and just trying to put your hand into the mouth of the oven runs the risk of getting burned. It's very very hot.

I also put my baking steel onto half of the firebrick floor. I did a measurement of the temperature and the baking steel is reaching almost 700f - the firebrick is around 600f. Maybe the baking steel is my answer to solving the poor heating of the floor. Hopefully I can bake a pie shortly and see how it goes once the flame dies down a bit.

[Oven_Man]

I took some measurements and found the following

Whilst the oven was very hot, the outside of the oven was around 170 to 180f.
The underneath of the oven was actually cold to the touch - you could leave your hand there indefinitely and not discomfort whatsoever. Infact to say it was even warm would be an understatement. This leads me to believe that the firebrick isn't losing heat to the bottom of the oven.
The steel got to around 700 to 750f and stabalized around there.
The firebrick got to around 600F
After the fire died down and the coals were almost out, the Steel measure around 450f and the firebrick around 350f

Not sure if these measurements can help someone diagnose my problem but I'm so desperate to fix this problem since I spent a small fortune to build this oven - I would hate for the oven to be almost useless.

[JRPizza]

Sorry to hear your oven is not living up to expectations. Without going back through your previous threads I'm curious how proven the design you used was. It seems like you have very little thermal mass in the floor and other than the inner shell none in the "dome". It's an unusual design (at least on this forum) which is why I was asking about the performance of similar (if any) ovens.

[deejayoh]

Two issues I see with the design that may be contributing to your heat-up issues
1) can't be 100% sure, but it looks like your design has the flue inside the oven? That means the heat could be going up the chimney instead of circulating. (Similar issue to barrel designs)
2) you have insulating material between your dome layers, instead of something that will retain the heat. So there is very little mass to heat up, possibly exacerbating the issue above.

[Petter]

Additional reflections:


Look at the fire management of this guy:

https://www.pizzamaking.com/forum/in...pic=41907.1400

The oven is also a low mass stainless dual layer.


Your opening is very wide and has full height across meaning it draws a lot of cooling air at floor level.

[Oven_Man]

Thank you all for your responses.

JRPizza, you are 100% correct. There is very little to no thermal mass in-between the domes. The floor just has 1" firebrick for thermal mass - I don't know thicker firebrick would make any difference.

deejayoh, I brought the flue as close to the oven opening as possible but I hear your concern that the flue and vent should be in front of the opening so hot air circulates properly in the oven before finding it's way back out the vent and flue.

Petter - I followed the guidelines for the opening - I kept the height at 63% of the inner dome height. Not sure what guidelines there are for the width but I went with a width similar to a brick oven.


I see Forno Bravo has the Bella Medio stainless steel oven https://www.fornobravo.com/PDF/bella...dio-manual.pdf and looking at the dimensions, mine are almost the same. Anyone has the Forno Bella oven and can comment on the effectiveness of this oven?

Something interesting happened yesterday - after I was done with the oven, I left it to cool off but a short while later it started to rain so i quickly covered it with a water proof cover. After more than 2 hours, I went to check on the oven if it didn't burn through my cover (thankfully it didn't) and I noticed the inside was still quite warm (stone measurement was around 200f and baking steel was about 300f compared to the previous day when I let it cool - as soon as the coals died, the oven cooled off within 20 minutes. It seems the cover locked in the heat which boggles my mind since the insulation should be doing the same.

I'm just hoping that using this kind of oven is a learning curve compared to a similar brick oven

[JRPizza]

I think your design is going to lend itself to more live fire cooking than retained heat cooking. It will heat up faster than a conventional brick oven and cool off faster too. Move the fire around enough to saturate your floor with enough heat to cook a crust and keep a fire going to one side to reflect heat back to cook the top of your pie.

[UtahBeehiver]

JR is spot on. The 1" thick floor will need to be replenished with heat more often. 2" is a minimum thickness for thermal mass on floors (even with 2", depending on the number of pizzas needs replenishing of heat). So you just have to adjust and factor in raking the to coals over the floor more often. Not much you do about the thermal mass on the dome other than keeping a live fire.

[Oven_Man]

I guess this oven is a learning curve - the more I use it, the better I hopefully get at making it work.

[MarkJerling]

Looking at your video and photo posted, I see a number of potential areas for improvement.

1. As your flue is going out from the top of the 'dome', you will see rapid heat loss. I'm guessing here, but I think you should see some improvement if you have a baffle so that you can retain some heat under the top of the dome. At the moment, all your heat will be sucked up the flue. You'd want that baffle to extend down behind the flue to a height somewhere between the door height and the top of the 'dome' height.
2. I see your base fire bricks are elevated above an air space. This is bound to provide convection air movement so your tiles will constantly be cooled due to air being sucked in below. I'm not surprised, therefore, that you're saying the underside of the oven is cool to the touch. As others have pointed out, you'll struggle to retain heat with such thin floor tiles.

As others have pointed out, this oven will function very differently to a brick oven - I believe we wrote about that in your design thread.
Good luck!

[Oven_Man]

Hi Mark

Thanks for your response.

I think you are correct - the flue is sucking away most of the heat since the flames actually travel up the flue instead of lapping the dome to the opposite side of the fire. I'm trying to understand a little more about the baffle - are your referring to a damper on the flue itself so i can open and close it? I'm actually going to ask my fabricator if he can add that on for me. I was also think of closing the flue off temporarily and see if that makes any difference.

Regarding the firebrick, yes it is elevated ontop of another piece of sheetmetal - I did this to help with the airflow underneath the brick but perhaps the though behind it wasn't all that good. I can easily remove the sheetmetal and let it sit flat on the base?

I wonder also if another design flaw maybe a contribution factor to the heat issue i'm experiencing. I have firebrick on one side of the oven only i.e. the right side and then on the left side of the oven I created a Steel Tray to hold the logs and keep the ash contained - this steel tray sits directly on the base of the oven. I'm wondering if the installing firebrick over the entire floor and then left my fire burn directly on the firebrick - will that help in any way?

[JRPizza]

Burning directly on the firebrick would help, as would eliminating the airspace below as MarkJerling pointed out. I'd consider adding some type of CF board on the bottom and making the layer of brick extend over the entire surface.

[MarkJerling]

Hi Mark

Thanks for your response.

I think you are correct - the flue is sucking away most of the heat since the flames actually travel up the flue instead of lapping the dome to the opposite side of the fire. I'm trying to understand a little more about the baffle - are your referring to a damper on the flue itself so i can open and close it? I'm actually going to ask my fabricator if he can add that on for me. I was also think of closing the flue off temporarily and see if that makes any difference.

Sorry for the delay in reply. We've been away from home. I was not thinking of a openable baffle in the flue, but rather a baffle at the top of the oven so as to prevent all the hot air which should be held at the top of the oven from going directly up the chimney. Let me know if you need a sketch.

Regarding the firebrick, yes it is elevated ontop of another piece of sheetmetal - I did this to help with the airflow underneath the brick but perhaps the though behind it wasn't all that good. I can easily remove the sheetmetal and let it sit flat on the base?

I wonder also if another design flaw maybe a contribution factor to the heat issue i'm experiencing. I have firebrick on one side of the oven only i.e. the right side and then on the left side of the oven I created a Steel Tray to hold the logs and keep the ash contained - this steel tray sits directly on the base of the oven. I'm wondering if the installing firebrick over the entire floor and then left my fire burn directly on the firebrick - will that help in any way?

While I think your contained fire idea has merit, it means you can't spread the coals over the whole floor and you can't move your fire location from one part of the floor to another - all features of a typical wood oven. I would consider removing the ash grate and pave the whole floor with firebricks and go from there.

[Oven_Man]

Hi Mark

Definitely going to brick the entire floor of the oven - also gonna remove the underneath plate that's creating an air gap.

If you don't mind, please can you sketch the baffle you referring to.

You truly have been a great help - can't thank you enough.

Take Care