How important is the heat break ?

[Dooozie]

I'm on my 4th course of dome bricks and doing the inner arch at the same time (now I've finally worked out the proper placement)
My floor bricks are not mortared, just butted up to each other as advised on here. I'm now wondering about the heat break between the inner and outer arches....
As my floor bricks are just sat on the insulation, the outer arch would be a separate structure just stood on the floor bricks. Is this correct ?

I can't get my head around the stability (or lack of) of the front arch. I have seen some professional builds where there isn't any heat break between the arches so, is it really that important ? Is it an option or a must do thing.

Thanks.

[rwiegand]

I'f you're worried about cooking for four days on one firing the heat break is probably important. For doing pizza one day and maybe baking something the next day it makes no difference as long as the rest of your insulation is up to snuff. A well-sealed, quality door will make many times more difference.

[david s]

The so called “ heat break does a reasonable job in preventing conductive heat loss if an air gap or insulating material is used, but at only around 1 cm, will do little to stop heat loss by radiation. For example, you wouldn’t expect 1 cm of insulation either under the floor bricks or over the dome to be of much effect. It’s primary function IMO is to act as an expansion joint reducing the stress on the cooler parts of the oven. There is a considerable difference in temperature between the oven chamber and the flue gallery as well as the flue gallery and the outer decorative arch and outer shell. The higher the temperature the greater the thermal expansion. The best situation is to allow the inner oven parts free expansion inside the decorative arch and the outer cement shell.

[mongota]

I'm the same.

I separated them more for independent thermal movement. I start my fires on the landing, the landing tunnel bricks get hot while the dome is relatively cool. Then the fire gets pushed back in to the dome, the dome gets super hot while the landing tunnel less hot. Different rates of thermal cycling, and with structure of the tunnel versus the structure of the dome, different vectors for thermal expansion.

My dome and arch bricks bear on the 4" of board insulation versus being stacked on top of the floor brick. Insulation board compression was a concern, For a while I worried about the weight of the chimney causing issues with board compression, and my tunnel "sinking" and contacting the dome. But it has not been a problem in any way, shape of form.

You can buttress the tunnel if you're worried about the tunnel stability. Mine is not buttressed, but it is a derivation of an elliptical arch. Had I done vertical sides caped by an arc, I likely would have buttressed.

[DavidApp]

I built my entry arch on blocks of Perlite concrete the same thickness as the oven floor insulation. The arch was separated during construction by cardboard. There is a noticeable difference in temperature of the inner arch and the outer arch. There is possible that the heat break may help reduce cracking in that area.
I should have made the chimney entry wider.

David

[DavidApp]

I have found my entry way photos.
The chimney entry bricks are cut so they go over the inner arch. I packed insulation in the gap when it was all cured. The entry way supports stand partly on the FB insulation and mainly on the cast blocks of Perlite and cement.

David