36" or 42"

[K79]

Re: 36" or 42"

I think it is more accurate to say the height of the dome will be "close" to the radius. Plenty of builders have planned that way and then been surprised when their oven is higher than they expect.

Using a design like what is shown in Hendo's post, the dome is going to be about inch higher than the radius due to the distance between the IT pivot and the floor. Protection layer over the floor bricks + IT pivot that is even higher than that. Result is that the arc of your IT starts that distance above your floor and raises the height of the dome. Couple of ways around this are to sink the pivot of the IT to the floor height (remove the center bricks) or use some sort of adjust on the fly IT. Couple of builders have used a turnbuckle in their designs to accomplish the latter.

I get a bit anal-retentive about this because I was flummoxed by it for a while when I was working out the math in my spreadsheet. Once it hit me it was obvious, but it took a while.

It now strikes me that I should modify said spreadsheet to give builders the range of suggested door heights!

Any way to get a look at that spreadsheet

[deejayoh]

Re: 36" or 42"

The Pompeii is a hemisphere, so if you use a "Hendo" tool, also known as an indispensable tool" to place the dome bricks, the oven interior height will be half of the diameter, a 20" interior height and 40" oven.

Chris

http://www.fornobravo.com/forum/f28/hendos-dome-gauge-nice-idea-2573.html

These tools can be very simple and easily made.. Highly recommended!

I think it is more accurate to say the height of the dome will be "close" to the radius. Plenty of builders have planned that way and then been surprised when their oven is higher than they expect.

Using a design like what is shown in Hendo's post, the dome is going to be about inch higher than the radius due to the distance between the IT pivot and the floor. Protection layer over the floor bricks + IT pivot that is even higher than that. Result is that the arc of your IT starts that distance above your floor and raises the height of the dome. Couple of ways around this are to sink the pivot of the IT to the floor height (remove the center bricks) or use some sort of adjust on the fly IT. Couple of builders have used a turnbuckle in their designs to accomplish the latter.

I get a bit anal-retentive about this because I was flummoxed by it for a while when I was working out the math in my spreadsheet. Once it hit me it was obvious, but it took a while.

It now strikes me that I should modify said spreadsheet to give builders the range of suggested door heights!

[SCChris]

Re: 36" or 42"

I concur with Deejayoh. The safe course is to follow the plans, however these ovens are very forgiving with regard to dimensions and even shapes. Remember however that it's easier to learn from others than forging something altogether new.

There is a wealth of knowledge about materials and mortar formulas. These are well known and proven and you will be delighted with the results.

Chris

[deejayoh]

Re: 36" or 42"

Ok, so lets just say I decide on building a 40" diameter oven. How do I figure the interior height so I can come up with the correct opening height?

Your interior can be whatever height you choose, it doesn't have to be the same as the radius of your oven. For instance, if you use an IT to build your oven, the height will usually be at least an inch higher than the radius of your oven because of the distance between the oven floor and IT pivot. I used a plywood form on my oven in order to have an 18" dome height on a 19.5" radius. So for my oven size, - the height could have ranged from 20.5" had I used an IT to 18" the way I built it. That's +/- 2.5" based on preference.

Also, the door height ratio you're talking about (60-65%, IIRC) is simply a rule of thumb - I think based on observations about the dimensions of old ovens in Europe. It is not some sort of hard and fast law based on physics. Applying the 60-65% rule to a 20" high oven - that's a range of +/- an inch in the door height based on builder preference.

So my $0.02 is that door and oven height are not tied to oven size by any sort of inviolable math formula. Choose the oven size you want, then optimize oven height and door height based on how you want to use the oven. Low oven domes are better for pizza-specific ovens, higher domes give better access for baking and big dishes.

[SCChris]

Re: 36" or 42"

The Pompeii is a hemisphere, so if you use a "Hendo" tool, also known as an indispensable tool" to place the dome bricks, the oven interior height will be half of the diameter, a 20" interior height and 40" oven.

Chris

http://www.fornobravo.com/forum/f28/hendos-dome-gauge-nice-idea-2573.html

These tools can be very simple and easily made.. Highly recommended!

[K79]

Re: 36" or 42"

Ok, I was wondering how to find out the inside ceiling height of a 40" dia. oven. That formula is to find the opening height isn't it?

[SCChris]

Re: 36" or 42"

The math would be, the radius of the oven times .667.
So a 40 inch diameter oven will have a 20" radius, the height of the interior, this number times .667, or 13.34 inches.

Chris

[K79]

Re: 36" or 42"

The plan ration is 66.7% of the oven height, I went by memory rather than referencing the plan. Go with the plans ratio. So corrected the 42 would have a 14" oven entry verses the 36 at 12".

Sorry for the confusion.

Sincerely

Chris

Ok, so lets just say I decide on building a 40" diameter oven. How do I figure the interior height so I can come up with the correct opening height?

[SCChris]

Re: 36" or 42"

The plan ration is 66.7% of the oven height, I went by memory rather than referencing the plan. Go with the plans ratio. So corrected the 42 would have a 14" oven entry verses the 36 at 12".

Sorry for the confusion.

Sincerely

Chris

[K79]

Re: 36" or 42"

K79,
I have a 42 and most of the time a 36 would be fine. I can say that when the oven is really full is when I have a roast and side dishes going. I don't think I would have been hampered with a 36 but when I made my choice I decided that since I had the room and a suckling pig was one of those things I wanted to roast, I went with a 42. A point not often discussed is the height of the oven entry. If my memory serves me, 60% of the interior height of the oven is what is felt to be the ideal entry height. So for a 42 the entry should be about 12.6 inches and for a 36 about 10.8. These 2 inches may be more important than floor space. Insulation is in my opinion critical and given you're in Maine I think you'd be doing yourself a disservice by cutting corners here. Also I think you want to think about some oven house and covered work area but these really depend on how you want to use the oven and how often.

Chris

I'm a little confused here. Not with the math just that it contradicts the FB plans. A 36" oven with a high ceiling height of 18" would give me a 10.8" entry according to your math. When I look at the FB plans they show a 12" entry? Can anyone clarify?

[V-wiz]

Re: 36" or 42"

Wow thanks, yes that does help, i plan on doing pizza, sometimes bread (i have no knowledge about this) roasts, grilling, a whole pig and lamb, large slabs of meat ( i am a meat guy) and any other cooling. So its seems like i will be building a 40" oven with lots if insulation

Thanks a lot

Answer this question first... will you be making only pizza or pizza and bread or pizza bread and other cooking? After using my oven for some time now, the best answer I could give is as follows: "it is all about thermal mass"
Pizza only - 38"- 40" built with small firebricks (8 1/4 inch cut in half) minimum insulation,(amount recommended in pompeii plans) would make a wonderful pizza oven. Little firewood, quick to get to temp and pizza galore.
Pizza and single batch of bread the next day - 38" 42" built with large firebricks (9 inch bricks cut in half) Lots of additional insulation and possibly a heat break between your oven and vent/landing area. An insulated door is a must! You may use a little more wood in order to get it up to pizza temps, but while you are cooking pizza you still have a fire going and are thoroughly saturating the dome for the next day's bread baking. So not a lot of "wasted wood" or heat loss. Would you use more wood here - yes
Pizza, multi-batch of bread and cooking a third and possibly a forth day - 38"- 42" dome built with large firebricks and add one inch of firebrick/concrete to the entire dome. (firebrick concrete is heat stop mortar or home brew mixed with the chips and fragments of firebricks you cut during the dome build. The pieces can be large or small, it just cuts down on the amount of plain mortar you use for cladding and gives it some resistance to cracking) Super insulate the dome and hearth, I would use 6 inch foamglas under the hearth and as much Kaowool or other brand of insulation on the dome and then I added loose vermiculite on top of the dome, to fill up the inside of the protective structure. You will use more wood to saturate the added thermal mass, but you will be able to cook for four days. It does not hurt to use the "super insulation method" on any of the designs, it is just more costly. It would be a waste of money and resources on a pizza only oven but not on any oven you will be baking with the next day.
I hope this helps answer you question. Good luck!

[Aegis]

Re: 36" or 42"

^ Beautiful, wow. I would love to hang out there.


This may sound weird but its going thru my mind if i would rather build a 40" instead of a 42" oven. Space is not an issue, neither is money or materials. I know for sure even a 38"-40" would be enough for me. Would a 40" oven take a noticeable less amount of wood to heat up the oven. I know the difference is VERY little but lets see what you guys have to say? Thanks.

Answer this question first... will you be making only pizza or pizza and bread or pizza bread and other cooking? After using my oven for some time now, the best answer I could give is as follows: "it is all about thermal mass"
Pizza only - 38"- 40" built with small firebricks (8 1/4 inch cut in half) minimum insulation,(amount recommended in pompeii plans) would make a wonderful pizza oven. Little firewood, quick to get to temp and pizza galore.
Pizza and single batch of bread the next day - 38" 42" built with large firebricks (9 inch bricks cut in half) Lots of additional insulation and possibly a heat break between your oven and vent/landing area. An insulated door is a must! You may use a little more wood in order to get it up to pizza temps, but while you are cooking pizza you still have a fire going and are thoroughly saturating the dome for the next day's bread baking. So not a lot of "wasted wood" or heat loss. Would you use more wood here - yes
Pizza, multi-batch of bread and cooking a third and possibly a forth day - 38"- 42" dome built with large firebricks and add one inch of firebrick/concrete to the entire dome. (firebrick concrete is heat stop mortar or home brew mixed with the chips and fragments of firebricks you cut during the dome build. The pieces can be large or small, it just cuts down on the amount of plain mortar you use for cladding and gives it some resistance to cracking) Super insulate the dome and hearth, I would use 6 inch foamglas under the hearth and as much Kaowool or other brand of insulation on the dome and then I added loose vermiculite on top of the dome, to fill up the inside of the protective structure. You will use more wood to saturate the added thermal mass, but you will be able to cook for four days. It does not hurt to use the "super insulation method" on any of the designs, it is just more costly. It would be a waste of money and resources on a pizza only oven but not on any oven you will be baking with the next day.
I hope this helps answer you question. Good luck!

[Aegis]

Re: 36" or 42"

I really wish I had one of those on both sides of the oven! It is more of a necessity than a architectural detail. Next build I will have two counters!

[K79]

Re: 36" or 42"

[QUOTE=Aegis;145861]I Agree with everyone! LOL I have a 42" Pompeii and love it! I do have plenty of room to work a couple of Pizza's at once. A 36" oven I can imagine would be able to handle at least two pies without trouble. They cook so fast it can become a mute point for more than two pies at once. Unless you are going commercial. Define for yourself how you want to use the oven, that is the hardest part. Not having an oven, you can only imagine how you are going to use it. The range goes from having a few pizza's once or twice a week, to using the oven for cooking over a four or five day period. The difference in 36 vs 42 is not only physical dimensions of interior volume, but also thermal mass. A 36" oven with 2.6" walls/floor and minimum insulation would be great for a quick heat up and throw a couple of pies in for a great pizza party! A 36" with 4.5" walls/floor added refractory concrete and HEAVY insulation will take a bit more wood and heat up time, but you will have lots of pizza(800F), bake bread the next day(550F), Cook chicken or casseroles(375F),then slow cook Lamb, Prime Rib, pork shoulder etc. (260F) So you have four days of cooking and then I load up the oven when it it down to 140F with wood for the next burn. So either will work for however you want to use it. You just need to build it that way. As an aside note I have had times when I have only had Pizza and do not have the oven saturated fully with heat. I just bring it up to 900F and then move the fire over to the side, clean the floor and by the time I am putting pies on the hearth it is down to 750-800F and pies are cooking perfectly! I just keep the side fire a little hotter, than when I have ful saturation.QUOTE]

I absolutely love your table you have extending out of your oven. I might have to do the same

[K79]

Re: 36" or 42"

You must have built a 36". Don't have dome envy. Maybe 30-40 extra bricks at a couple bucks a peice for an added 36.11% increase in floor sapce. Also I use 10 peices of almond wood to get my oven to temp and it keeps because of the efficiency of the insulation. K79 dont cut corners on something you will probably use for the rest of your life. Plus you guys in Maine must be rich, look at how much lobster you eat. Bigger is better. At least that's what my wife says.

Thanks for the info guys. I'll need to think it over and discuss with my wife. By the way, up here in Maine we take the lobster off the boat, start a fire on the beach, put it out and wrap a crate of lobster in seaweed and put it right on the coals. Best way to have it !!