Heat Drops fast!

[dimitrisbizakis]

Re: Heat Drops fast!

It sounds like the cause of your issue is the 30 cm of vermicrete under the floor, which is probably still wet. As the base of the dome and the insulation under the floor are the hardest to dry out, try spreading the fire to the base of the dome and just keep feeding it all day if possible. If it's wet down there you will probably notice a persistent ring of black soot which is also an indicator that the oven is still wet there.
If you are trying dry the oven leave the door off and the coals in.

I will try your advice my friend, thank you for your help.

[dimitrisbizakis]

Re: Heat Drops fast!

The ovens wet.

...damn!Curing fires are so boring...

[david s]

Re: Heat Drops fast!

Today, after 7 hours, the oven was at 100c, that is without embers inside and with the door on.
Em i supposed to leave the door on?
I have a thought that the moister would not have a way out.
And another question, do you wait for all the wood turn in to embers and the you rack them out?
I'm saying that because after i throw 2 pieces of 4 cm of olive wood on each side of the oven, they ignite of course but after a while the just stopped burning.Fearing that the heat will start dropping because the fire went off, i remove them so the embers and closed the door.

It sounds like the cause of your issue is the 30 cm of vermicrete under the floor, which is probably still wet. As the base of the dome and the insulation under the floor are the hardest to dry out, try spreading the fire to the base of the dome and just keep feeding it all day if possible. If it's wet down there you will probably notice a persistent ring of black soot which is also an indicator that the oven is still wet there.
If you are trying dry the oven leave the door off and the coals in.

[brickie in oz]

Re: Heat Drops fast!

they ignite of course but after a while the just stopped burning.

The ovens wet.

[dimitrisbizakis]

Re: Heat Drops fast!

Sorry, I got you mixed up with Tonybaker's oven. Have you got insulation under your floor? A new oven contains a lot more moisture than you would think and it takes a lot longer to drive it out than you would think. If you've only had two fires in it then that is insufficient to remove all the water. Keep firing and cook some stuff in the oven like roasts and bread, forget pizzas for now. You should start to notice an improvement in the ovens performance, ie. less smoke, quicker temp rise and more even heat distribution. It sounds like the top of your oven may be dry while the bottom and floor is still moist.

Today, after 7 hours, the oven was at 100c, that is without embers inside and with the door on.
Em i supposed to leave the door on?
I have a thought that the moister would not have a way out.
And another question, do you wait for all the wood turn in to embers and the you rack them out?
I'm saying that because after i throw 2 pieces of 4 cm of olive wood on each side of the oven, they ignite of course but after a while the just stopped burning.Fearing that the heat will start dropping because the fire went off, i remove them so the embers and closed the door.

[david s]

Re: Heat Drops fast!

Sorry, I got you mixed up with Tonybaker's oven. Have you got insulation under your floor? A new oven contains a lot more moisture than you would think and it takes a lot longer to drive it out than you would think. If you've only had two fires in it then that is insufficient to remove all the water. Keep firing and cook some stuff in the oven like roasts and bread, forget pizzas for now. You should start to notice an improvement in the ovens performance, ie. less smoke, quicker temp rise and more even heat distribution. It sounds like the top of your oven may be dry while the bottom and floor is still moist.

[dimitrisbizakis]

Re: Heat Drops fast!

If you had used dense firebrick for your floor and dome, after a two hour burn the oven temperature would be in the region of 400 C

What do you mean if?
I'm not the guy with insulation firebricks m8
I have build my dome with solid red clay bricks and floor with firebricks.
At firing the temps rise up to 500 c, perhaps moister is still there and I have to be quicker with the coals racking out...
When is the perfect time to remove the coals without losing to much heat?

[david s]

Re: Heat Drops fast!

If you had used dense firebrick for your floor and dome, after a two hour burn the oven temperature would be in the region of 400 C

[dimitrisbizakis]

Re: Heat Drops fast!

Ok, new data about the temp drop!
Today i did the Second burning with the insulation and render layer on, I previously burned the oven one more time without the insulation and the render.
After the soot have gone I've added some wood, total burning time 2 hours approximately.
After removing the coals i placed my door,the door temp stopped rising at 226 C, the outside of the dome wasn't even warm at touch.
After an hour passed with door closed the temp dropped dramatically to 165 c, and the oven was slightly warm at some spots on the top of the dome.
I have an internal oven thermometer that showed 260 c but the Mississippi count go beyond 10 so i guess the door thermometer was right.
Please give me your thoughs!

[brickie in oz]

Re: Heat Drops fast!

sorry, I forgot to say that on the floor of the oven in the middle are some very special high density bricks that act as a heat sink.

Not that special if the oven doesnt retain heat for any time.
An oven should retain heat for a week.

I agree entirely with your thoughts and they make sense, however the oven works fine and the perlite bricks were so easy to cut.

Good functional ovens are hard work to build, theres a trade off here.

I could always throw some railway irons into the base if it became a problem with heat storage?

Scrap iron pizza?

[dimitrisbizakis]

Re: Heat Drops fast!

sorry, I forgot to say that on the floor of the oven in the middle are some very special high density bricks that act as a heat sink.
I agree entirely with your thoughts and they make sense, however the oven works fine and the perlite bricks were so easy to cut.
I could always throw some railway irons into the base if it became a problem with heat storage?

If this works for you is ok m8!

[tonybaker]

Re: Heat Drops fast!

Oops, sorry m8 brickie in oz is right!
Exept if we misudenrstude something.
You could build an inner layer to your walls and floor with firebricks, its a hard way and you will reduce the size of your oven but the other way is to start all over.[/QUOTE]

sorry, I forgot to say that on the floor of the oven in the middle are some very special high density bricks that act as a heat sink. \

I agree entirely with your thoughts and they make sense, however the oven works fine and the perlite bricks were so easy to cut.

I could always throw some railway irons into the base if it became a problem with heat storage?

[dimitrisbizakis]

Re: Heat Drops fast!

Theres your problem, perlite is an insulator not thermal mass.
You need to build an oven with thermal mass and save the perlite for the insulation.

Oops, sorry m8 brickie in oz is right!
Exept if we misudenrstude something.
You could build an inner layer to your walls and floor with firebricks, its a hard way and you will reduce the size of your oven but the other way is to start all over.

[brickie in oz]

Re: Heat Drops fast!

The oven bricks were perlite as were the floor tiles, very light and easy to cut with small angle grinder. .

Theres your problem, perlite is an insulator not thermal mass.
You need to build an oven with thermal mass and save the perlite for the insulation.

[tonybaker]

Re: Heat Drops fast!

my dome insulation is perlite and mortar mix, about 4 inches thick. There is another 2 inches of plain mortar over that for weather proofing. When the oven is at operating temp you can hardly feel any warmth on the dome. I have a thermal break between dome and outer arch, this makes quite a difference. My door is 3/8 steel plate, first one was wood - lined with sheetmetal, it only lasted two firings! The oven hardly needed any drying out

My oven floor sits on hollow blocks, not mortared nor backfilled with concrete. It was super easy to build like that.

The oven bricks were perlite as were the floor tiles, very light and easy to cut with small angle grinder. At first I agonized over setting out the bricks but soon realized that it doesn't matter too much if things are not perfect. I made sure I did not use any mortar to fill any gaps inside the dome as I was afraid of falling cement getting into my pizzas at a later date. The fit between the bricks was reasonable and the whole setup works very well.