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-   -   How to get brick oven HOT? (http://www.fornobravo.com/forum/f48/how-get-brick-oven-hot-20205.html)

edjc 12-12-2013 08:52 AM

How to get brick oven HOT?
 
I built an outside dome brick oven: Bricks, Insulation, Cement vermiculite insulation layer on the top.

48 " inside round.

Smoke Vents out the front door.

My questions:
Should I build then start my fire near the door?

How long might I expect to burn the fire in order to get it pizza oven hot?

I'm in cold, snowy New England:confused:

boerwarrior 12-12-2013 09:01 AM

Re: How to get brick oven HOT?
 
yes, start the fire near the front door and then push it back when you have good heat.

Is your oven cured? You didn't mention insulation in the floor.

If your oven is cured and well insulated all the way round, you should expect to be able to get it really hot in 1-2 hours. It takes me exactly 75 minutes to get my oven to temperature (for pizza) when it is 40 degrees out. But my oven is only 32 inches.

edjc 12-12-2013 10:11 AM

Re: How to get brick oven HOT?
 
Cooking surface is fire brick

Beneath that is base: 3" of cement and vermiculite base

stonecutter 12-12-2013 01:09 PM

Re: How to get brick oven HOT?
 
Quote:

Originally Posted by edjc (Post 166669)
I built an outside dome brick oven: Bricks, Insulation, Cement vermiculite insulation layer on the top.

48 " inside round.

Smoke Vents out the front door.

My questions:
Should I build then start my fire near the door?

How long might I expect to burn the fire in order to get it pizza oven hot?

I'm in cold, snowy New England:confused:

If your oven is dried, are you using dry wood?

What is your flue size? How tall?

How wide is the throat? An undersized throat is arguably the biggest reason smoke bypasses the vent area and comes out of the outer opening.

david s 12-12-2013 01:13 PM

Re: How to get brick oven HOT?
 
All ovens will tend to be smokey when they're new and wet too.

edjc 12-12-2013 01:14 PM

Re: How to get brick oven HOT?
 
No chimney in my design

My oven is 20 days in of 29 day cure time

My wood dry split hardwoods

How long might I expect to have to pre burn my fire in order to heat oven up for pizza cooking

david s 12-12-2013 01:35 PM

Re: How to get brick oven HOT?
 
You don't say how thick your floor or walls are, but if you have had fires going for 20 days it should be dry. Most ovens will start burning the carbon off the roof of the oven after about one hour at which point you should have the dome filled with flames. After around an hour and a half the whole dome should have gone white. If cooking more than a few pizzas keep firing for around two hours. If it takes longer than this then your oven may still be a bit wet or your walls are really thick.

wotavidone 12-13-2013 05:17 AM

Re: How to get brick oven HOT?
 
1 Attachment(s)
Quote:

Originally Posted by stonecutter (Post 166678)
How wide is the throat? An undersized throat is arguably the biggest reason smoke bypasses the vent area and comes out of the outer opening.

I have tried to draw this out in paint. For the purposes of drafting, smoke can be considered a liquid, which has velocity as it come out of the oven. It needs to be turned to go up the flue, and it won't do a sharp right angled turn.
The flue is a compromise, we try to make it fairly big, but we don't want to have to far to reach into the oven.
The layout on the left in my crude drawing is what most of us build, wide across the oven, and not very deep.
It doesn't leave much distance for the smoke to make the turn, especially when we have the most smoke and the least draft, at the beginning before things heat up, and we ask the smoke to spread laterally.
I reckon the layout on the right would work better because it would leave more length for the smoke to make the turn, but it would mean we have to reach a long way to get into the oven.
I note though, that the oven being discussed here vents out of the front and doesn't have a chimney, so I guess my ramblings are irrelevant.
My oven started as just a dome with an opening in it. I had a stainless steel hood perched above the opening to funnel the smoke away. The theory was good in still air, but in practice there almost never a completely wind free day here. I ended up building an arch in front of the oven. This made a big difference to heat up times. With the new arch, I was also able to use what most people call a blast door. This excludes the wind, while letting combustion air in the bottom cut out. End result, when it's windy I get a much faster, smoke free heat up. Not a lot of difference on a still day.

david s 12-13-2013 10:20 AM

Re: How to get brick oven HOT?
 
Yes, it works really well. Too well in fact. The resulting temperature rise from ambient to 400C in less than an hour is the outcome. It would be the equivalent of firing a kiln with the burner on full from the beginning. The problem is that the rapid temperature rise creates uneven expansion which can lead to cracking. If you want to be kind to your refractory don't use a "blast door" below around 250 C or at around 400 C.+ These are both temp ranges where damage is likely to occur from rapid temp rise? If you don't really mind cracks in the oven then ignore this advice, your oven won't fall to bits. I prefer to take it slow and steady and allow the refractory to adjust itself in its own time. My mobile oven has quite a few cracks because when I hire it out people decide to see how hot they can get the thermometer and how much flame they can get up the chimney, while my oven at home (same design) is in pristine condition.

wotavidone 12-13-2013 03:58 PM

Re: How to get brick oven HOT?
 
Yes, it can be scarily quick. I address this in much the way you have mentioned. I only made the door because I needed a draft excluder, not as a way of accelerating the burn, and don't put it on until the initial thermal shock is over.
The outer door has a way of directing the air straight onto the burning timber, hence the moniker "blast door" and things get bloody hot bloody quick. I can't limit the air much, since I don't have any fancy adjustable vent on the door, so I limit the fuel in the oven once the door is on. I really must come up with some adjustable set up.
Until I made this door, I had an oven that would heat to white in less than an hour on a still day, and struggle to get to temperature at all on a windy day, even though I took care to build it with the door facing away from the prevailing wind. The outer arch was a big improvement on its own, though.

When your oven is exposed to the elements, especially when the air is below freezing, (I simply cannot imagine what living in that sort of climate would be like) a door like this would help a lot to retain heat and exclude the cold winds.
Of course you need an outer arch and a chimney before you can use it.


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