Heating Time vs Size

[SchillerM]

I have tried searching and can't really find good details, so hopefully can get some better answers by posting...

I am wondering how long each size oven takes to heat. I am in planning stages and thinking in the 30" area. I get home later in evening (9ish) so heating time is a strategic concern, don't want to be cooking at midnight.

The things that I am interested in seeing are
Oven size
Full temp heating time (and temp that is considered full to you)
Amount of wood needed
Amount of insulation
Temp 24 hours later

Another question I have is reheating. If 24hours later its at 500F, what does it take to get it back up to temp? Time and material.

Thanks all.
Look forward to seeing the answers so I can decide on size I want to build, and then get building

Matt

[Tscarborough]

Re: Heating Time vs Size

If quick heat time is the most important factor, you may want to go with a cast oven instead of a brick one.

Conversely, if you will only be cooking a pizza or 2, you do not need a full heat soak.

As for time to fire, x amount of btus will heat x amount of mass in x amount of time, so for a given size fire, a larger (and/or thicker) oven will take longer to heat soak.

Bringing a heat soaked 500 degree oven to pizza temps is a short firing regardless of the size.

[WJW]

Re: Heating Time vs Size

I doubt you are going to find detailed studies/answers on that stuff because there are so many variables. That being said, I'm sure you will get some general rules of thumb.

My take on your questions are...

1. Oven size vs Heating time.: I don't think there is as much correlation as frequently claimed. What certainly is true is that a larger oven will consume more wood to heat up in a given amount of time than will a smaller oven. My oven is pretty big as residential ovens go (hearth is 36 wide by 42 long). If I turn the inside into a raging inferno it's going to heat as fast as a small oven stuffed with wood.

The variable which is more significant in my mind is how "thick" is your oven. Obviously, if there is six inches of cladding around one oven, that oven will take longer to saturate than an oven with very little or no cladding. But the surface temps of the bricks will heat quickly in any oven so long as the oven is full of fire.


How long to heat:



In the pic above the roof is just starting to clear. If I am really pushing things I think I could get sufficiently saturated in the hearth to cook a bunch of good pizza about ninety minutes after lighting the match. Understand...I would not be fully saturated, but you don't need to be fully saturated to cook pizza. If I were only going to cook two or three pizzas, I could probablly do it in an hour. The oven would not be fully cleared, but the hearth would be over a thousand across the entire surface. Once the coals were pushed to the side and the bricks brushed that temp would fall as the meat migrated away from center, but with a lot of active flame in the oven, and by cooking on different areas, you could get it done without trouble.

To completely saturate for pizza (assuming I were doing a very big party) means to me that the deepest layers of masonry would be 500-600 and the surface would be around 900-1000. At that point I would move coals to the side, and scrub bricks. The surface of the hearth would drop to 800 or so and I'd be in business. With that level of saturation I could cook two minute pizzas for hours. As the hearth surface would slightly cool, it would be recharged from the active flame in the oven. Additionally, cleaning the occasional charring off teh hearth by adding coal would reecharge as well.

For me to charge my oven to that point takes about three to three and a half hours. But that is only needed for very big party. My typical firing time before starting pizza is two hours before I want to start cooking. Maybe two and a half.

If the oven is already hot, the times fall dratically. If my oven is already at five hundred it is ready to cook within twenty minutes of firing...maybe thirty max.

Insulation:

As much as possible. I have three to four inches of Insblock19 and ceramic blanket around the whole thing...plus four to six inches of perlite sitting on top to fill in the enclosure. After blazing all night long, the oven is barely warm to the touch on the outside. Maybe 85 degrees when the ambient temp outside is 75 degrees.

[texassourdough]

Re: Heating Time vs Size

The correlation is not between size of oven so much as wall thickness. The thinner the walls the faster it heats up (but the less heat it retains for cooking later. I have a 1 meter Casa oven with an extra inch of refractory cladding (about 3 1/2 inches total thickness) and it is routinely up to cooking temp in 45 minutes. I can, in fact have it overheated in 45 minutes and have to wait for it to get down to pizza temps. But being fast is a function of how well you build fires and how big a fire you are willing to build! And the kind of wood you use. While insulation is important, it is not a significant factor in speed of getting the oven to pizza temps. You basically have to get the oven to clear (which indicates a temp of around 750 on the surface of the dome), have the hearth heat loaded (which means not having a bunch of ashes insulate it which is a problem some people encounter), and keeping a decent fire going on the side. It typically takes at least an hour and a half to heat saturate even the thinnest refractory oven and often much longer! As others indicated, you don't need to be heat saturated - but do recognize that when you are not heat saturated the refractory will be sapping heat from the oven so you need a bigger fire to compensate and keep the oven at proper temp!

Jay