How big should my dome be????

[hulkiebear]

Ok, I have built my concrete slab platform for my oven, it is 150 x 150 (5' x 5'). I originally wanted to build an barrel style oven(due to easy of building and my apprication for the shape of the oven) But now, after finding this forum, I have decided that a dome oven is a better and achievable design.

So now I need advice on what size dome I need. Whilst I like the idea of holding a pizza party and cooking pizza's all night long, the man in me says, "it's easy, as big as possible!"
Realistically, it will be 3-4 of us to cater for. So, I don't want to have to plan a day ahead to fire the oven up. I would like to get home from work, maybe clean out the oven from the night before, load up with wood, set it off, and get the pizza's ready for cooking whilst s'uping a pint of cider!

So, I see that sizes can go as small as 30" (internal dia) upto 42"(or loads bigger), so my question is...

How big is yours, and how man people can you satisfy?
(sorry, a carry on moment there! )

Seriously, what size do you all think is good for me?

[Les]

Re: How big should my dome be????

I have a 42 inch oven and feel I made the right choice. It allows plenty of room to cook while the coals are on the perimeter. I can get it up to heat in 3 hours (sooner if I go nuclear). A 60 inch platform will only allow you around 2.5 inches for the enclosure thickness (42 inch oven) ? that almost forces you to go with a dome, unless you make it smaller.

Les?

[dmun]

Re: How big should my dome be????

My oven is 36. It'll hold a big pile of coals on the side, and a couple of pizzas, or a pan of chicken parts roasting while i make pita breads. Remember, pizzas cook in a minute and change, and unless your stretching, topping, and loading pizzas with a crew, you are unlikely to get more than two in at a time. Can it get crowded? A bit. The ideal domestic oven may be one meter, 39.5 inches. Remember the volume increased exponentially with the diameter, you're heating (and buying) a lot more masonry with the bigger oven.

If you have a five foot square base, and a minimal thickness covering, you have sixty minus eight, for insulation, minus eight for brick thickness for a maximum of 44 inch floor, which is bigger than any domestic oven needs to be. Remember your entry needs more space, which will reduce the size of your floor unless you angle it to the corner.

[wlively]

Re: How big should my dome be????

I love my 42". It easily handles our family of 4 as well as extended family get togethers.

Based on your comments you could probably go smaller. Just have to ask yourself how much room you want. Try mocking up the size with card board and see how it looks. Unless you go with a thin dome, I don't see that much difference in heat up times between the sizes to really notice.

[Rastys]

Re: How big should my dome be????

Why go circular or barrel vault?
With a little creative cutting of your bricks, a round cornered square or even rectangular dome could give you all the room you would ever need.
I built a 40" or 1 metre Pompeii and I get at least 5 x 10" pizzas in at once (but as it has already been mentioned, when very hot, cook in around a minute or less. I only pack them in once the oven cools a little giving more time to manage the load.
If I was to build again, I would make a round cornered square low vault dome!

Rastys

[hulkiebear]

Re: How big should my dome be????

Wow, thanks for the replies everyone!

Now I have round cornered square dome thrown in! More to think about!!! phew...

Ok, low or high vault? I assume that a high vault would be a couple of courses or fire bricks then a perfect half sphere ontop.
So a low vault would be a much shallower curve in the sphere ontop!
I was thinking about this, and had an idea of how to achieve it with a modified indispensible type tool(clamp on end of threaded bar on pivot type thing), but how shallow is too shallow? and what are the pros and cons!

It's raining today, so I am siting down to design my oven and work out the amounts of materails needed today! so any further input would be great!

Lee.

[hulkiebear]

Re: How big should my dome be????

I have made a diagram that shows the floor coverage of a dome shape, the red being a 36" perfectly round dome, then the grey and blue ones are rounded squares, well, to be honest, they are just round shapes with the four quarters expanded out 20cm(8").

Looking at this, the same surface area of the floor is about the same for a 36" round for a 34" rounded square, and a 32" rounded square isn't that much more smaller!

I don't think this will be that hard to build as it is just an extra arch of whole bricks up in the middle.

opinions?

Lee.

[Wiley]

Re: How big should my dome be????

Kulkiebear,
One thing to keep in mind is what else are you planning on fitting in your oven to cook besides pizza. The "books" indicate somewhere close on a ratio of height of entrance to height of interior dome at 63% makes for best gas/air flow. That is the sweet spot where air flows in across the hearth and up over the dome's inner surface and out either the entrance or out thru a chimney efficiently. Now we get to a matter of opinion and not too any honest to goodness hard facts...does a smooth surface make for an easier gas flow and therefore better draw? Does a geometrically perfect shape (ellipsoid or hemisphere) make for smoother flow than a square oven with hard corners? What effect does corners have on heat reflection? Does anybody really know?

Most of us have stayed fairly close on the 63+- % ratio and have ovens that work. So my suggestion would be to decide what you want to cook and work backward from there. If just pizzas then a low dome and low entrance would be fine. If one wants to do the Thanksgiving turkey, or pork shoulders then perhaps a higher entrance (and therefore higher dome height) might better meet your needs.

Hope this helps some, it's the decisions that are the hard part.

Oh yes, my oven is 40 inch and I find that more than adequate for all my needs. If fires fast (40 minutes from match to pizza temps, tho longer for retained heat for bread and roasts).

Wiley

[hulkiebear]

Re: How big should my dome be????

thanks Wiley for the response.

Your account of firing up your oven and being pizza hot in 40 minutes sounds great for me. Whilst I always thought it would take longer, if I could acheive that, then I would be very happy!

Whilst I don't want this oven to be just for Pizza's, I still want it to be best at doing that(if that makes sense).

I will definetly stick to the 62-63% enterance hieght rule. If I go with the rounded square shape oven, this also lowers the hieght of the vault slightly, which will help to make it more pizza orientated(right?)

So, at present I am aiming at a 34" rounded square dome, with an initial flat course of Fire bricks before the dome starts, this will give a 389mm high vault, and a 450mm (18") wide enterance, being 245mm high. Obviously these measurements will vary depending on the accuracy of my workmanship!
So, yesterday, I picked up 140 fire bricks and a bag of refactory castable.
Today, the hearth will go down, and I will lay out the bricks to see how it looks in real life!

[muppety1]

Re: How big should my dome be????

Reading the posts on here i think the only answer is -as big as you can afford- or have space for. I have today started my 1st 'chain ' in the dome,-a 36 incher- i've decided on upright -whole brick - after which I am starting the actual dome with a 3/4 " spacer to give me a 20" , (very ish, )height inside the dome.Door is 12 " x 18"

I must admit that even after reading all the plans and posts on here , I still find it confusing , and I am winging it a bit ( as we say in norfolk) with some of the design factors, some of the materials are very hard to find in the uk.

[cynon767]

Re: How big should my dome be????

Maybe I'm missing something, but I'm not sure I can see the advantage of a round-cornered square dome. It seems to me that you'd only be gaining a little extra floorspace for a lot of extra fancy brickwork squinching in the corners, and ending up with something that may not be quite as strong structurally. I'm not an engineer or an architect, but I've always been under the impression that the reason a barrel vault requires more reinforcement is the fact that the outward thrust is perpendicular to the wall; wouldn't a squared dome have many of the same problems?

[hulkiebear]

Re: How big should my dome be????

The design I am playing with at the moment, is basically a circular dome, split into 4 quarters, expanded out enough to fit an arch each way. As my slab is constructed and I am tight for space, gaining a couple of inchs is really important, and as the arch in between each quarter section can be constructed first and is a straight forward arch with no cutting, this will actually mean less fancy cuts! Also, I can construct each corner one at a time.

The barrel oven needs so much support because it has a shallow arch which pushs out, as the arch in my dome is still as good as a half circle, it will need alot less support, but this is not an issue, I will tie in a concrete sleeper at either end of the arch into the slab to prevent any outward force.

[Rastys]

Re: How big should my dome be????

It sound like you have it all sorted and now know where you are heading! Great stuff hulkiebear, go for it. I'll be keen to follow your progress.
A lot of people seem to believe that a perfectly symmetrical/spherical dome is going to reflect the heat back down to the floor like a lens manipulates light.
I have a different theory that the dome is merely a heat 'sponge' to absorb and then to emit heat within the oven to providing the cooked item with radiated heat from above rather than just from below (the hearth).
A round cornered square oven will give the biggest and most economical floor space that is available but not necessarily built with almost vertical walls and "squinched" as cynon767 suggests. Select maybe a 32" oven plan and put a couple of extra bricks in the width and length to fit you base.

[hulkiebear]

Re: How big should my dome be????

Thanks for the encouraging words Rasty, I have started a post in the Getting Started section, showing my progress on this project! I won't be explaning absolutely everything I do, so as not to bore anyone who reads it, as you guys are my only remaining audience that will take any interest(wife seems to be a bit bored of me talking about it!). But will be glad to answer any questions in detail!

I agree about the heat sponge thing too Rasty, I don't see how the dome can focus heat on one point, unless the food is in the very centre. Also, as there may not be a fire all of the time, heat will not be reflected from one point to another point, but will simply radiate from the dome, so I don't think my design will cause much difference from a true round dome,

I have starte with a 26" dome design, split the four corners and added an extra 8" in between. I think this will give me a similar oven floor area and volume to a 36", but will give me precious 2" to spare!

It may all work, but, we will see, interesting to say the least!

[cynon767]

Re: How big should my dome be????

Thanks for explaining that...I wasn't seeing it at first. It sounds like it will be very interesting... can't wait to see pics!

Although, I have to admit, it's still easier for me to visualize thinking of a 36" dome with the sides cut off... is that still incorrect?