Vent/Opening and Heat Conductivity

[threestring]

I'm thinking about how to build the vent and opening for my oven, and most of the pictures I've seen so far show the corridor leading into the opening to be constructed out of fire brick. Wouldn't using a conductive material like fire brick or terracotta pull heat out of your oven? Wouldn't clay brick or something more insular help hold in the heat?

So, has anyone had problems with heat bleeding out the opening structure? And has anyone done anything creative to prevent this? Or is it not that big of a problem? Any advice is much appreciated!

Ethan

[james]

Welcome Ethan,

How did you come to be in Japan? It will be fun to see photos of your oven going up in the context of a Japanese neighborhood.

Good question on the vent material. Both firebrick and clay bricks are thermal, in that they absorb and hold heat -- as opposed to insulators such as Infulfrax, SuperIsol, vermiculite, perlite, insulating firebricks, etc. which are pumped full of air holes and block heat. It is OK building your vent and vent walls from either firebrick or clay brick, as it doesn't get too hot in the vent area and it does not see direct exposure to flame.

There isn't a problem with the vent being made from a thermal or refractroy material, as it is good for the vent to get hot and draw hot air from the oven, and promote convection. It is far enough away from the serious heat so that it does not wick heat from the oven.

In fact, the vent walls and vent pieces for othe Casa oven are all made from the same material as the rest of the oven. The vent walls are built into the pre-cast dome pieces.

Hope this helps -- I am looking forward to seeing some local photos.
James

[Hendo]

James,

What you say makes perfect sense for direct pizza cooking. I plan to have firebrick out to and including the oven door opening, then make a transition to red clay brick on the sides and front of the vent chamber, as well as above the oven for the chimney. The MTA oven (see pic) shows how I plan to do it, except that the sides of my vent chamber will be straight rather than angled, and be of clay brick.

I have to have clay brick anyway on the sides of the vent chamber, as these will be situated in the middle of my bench top, and only one brick thickness thick. So done for appearance more than practicality.

I’m also wondering if it would be a good idea, in the transition from firebrick to clay brick, to have a small gap (having regard to structural considerations) and stuff the gap with insulation blanket. Above the vent chamber, I was thinking of isolating the flue/chimney (which may simply be a single leaf of clay brick) with either some insulating firebricks, or like Drake, with some sort of cast insulating refractory material.

The only reason I'm considering going to this trouble is for bread baking – I thought with these insulating ‘barriers’ there might be less heat drain from the oven after the fire is removed.

Comments?

Paul.