Heat up time

[v12spirit]

I want to build a custom oven for my kitchen and don't see the point in waiting almost an hour to get it hot enough in order to use it for a few minutes which are suffecient to bake 4 jambo pizzas which are too sufficient for a feast.
Can I speed up the heating time by minimizing the thermal mass thickness (bricks) to almost 1"? If I can't what is the minimum thickness possible provided that I'm not gonna use the oven for more than almost 30 minutes every time so there is no worry of the floor cooling down by continuous baking.

[david s]

The short answer is no. Refractory materials are not particularly conductive and take time to heat up. If you want faster heat up times then you would be better to use a material like steel. A thinner refractory floor and dome will result in reduced strength. I should think that 1" would be about the limit. Surprisingly a smaller oven still takes about the same time to heat up as a larger one, probably because the fire in its chamber is proportionately smaller.

[Lburou]

FWIW, the heat up times were a stumbling block for me too. But, I got over it. The time spent bringing the oven to temperature passes quickly, and I enjoy it. You probably will too.

Don't forget, you can bake the next two or three days with no additional heat, if you follow the pompeii plans. It does not have to be the four pizzas and done.

[v12spirit]

Hi Lurou,
What are the heat brakes? I didn't find them in the glossary.

[v12spirit]

Thanks Davids
How about using a sufficiently thick steel board for the cooking floor directly over the insulation while using bricks for the walls and dome. Is there a risk of incosistent browning effect on the pizzas on top and buttom. I mean the pizzazs are brown on top while burned on buttom.

[david s]

Hard to say. You might just have to build it to find out. Part of the reason a firebrick floor works so well is that it is porous, which means moisture is sucked away from the pizza base or bottom of a bread loaf. People who use trays to cook their pizzas find that it traps moisture there resulting in a soggy crust. I would assume a steel floor would give the same result.
The steel being denser will heat up faster and presumably cool faster too.

[Lburou]

Originally Posted by v12spirit

Hi Lurou,
What are the heat brakes? I didn't find them in the glossary.

Its all about how long we can keep the heat inside the oven with just one firing.

With insulation under the floor and around the dome, the oven entry is responsible for most of the heat loss after the fire is out. The heat breaks/brakes are an attempt to slow the heat loss at the oven entry. Its a recent design tweak, and not necessary -but nice to have.

Maintaning heat longer allows us to bake something the next day or two, even three days after pizza. HTH

[SCChris]

The heat breaks mentioned are located between the oven structure and the entry and chimney areas. The chimney and entry are essentially open to the ambient temperatures and the brick structures that connect these and the oven act as conduits for the heat to move away from where you want the heat, in the oven.

The FB plans don’t address this area and regard the heat loss as acceptable, and this is not wrong thinking. The heat breaks are more difficult to engineer, harder to build into the project because of the dissimilar materials needed for these breaks.

The benefit of the break is that once the oven is charged the cooking time is extended, from 2 or so days to 3 or so. The majority of cooking time gained is at the higher cooking range, from pizza heat down to the 325F / 160C area. This higher heat moves out of the oven heat faster like water out of a leaky hose. These higher temperatures have greater pressure and move quicker through whatever path is available than lower temperatures do.

If all you care about is pizza then breaks are more work with very little pay back, if you want to maximize what can be cooked in the oven on a single charge breaks will pay for themselves as long as these are engineered properly and don't compomise the structure.

Chris

[mrchipster]

Originally Posted by v12spirit

Hi Lurou,
What are the heat brakes? I didn't find them in the glossary.

Heat breaks can also contribute to much lower outer surface temperatures on items such as the decorative arch and entry area. I used a heat break at the dome to flue arch transition, oven floor to flue arch floor, and flue arch to decorative arch. I am seeing 400 degrees after 3 days and over 200 at day 5 with outside temps averaging 20 degrees.

I have over 12 inches of insulation on top and 4 - 8 inches on the sides, 4.5 inches under the floor, and a 4 inch insulated door.

Chip