Insulation information

[dusty]

Hello Everyone!
I am building a 42" oven in Sac., CA. I have finished the hearth, set the floor, but I haven't started on the dome yet because I think I may have an insulation issue.
Let me try to discribe my potential problem. My square hearth is only one inch wider than the outside of my dome. That is, on the four sides of my dome, where it touches my enclosure, I only have room for 1" of insulation. At the corners, and up the sides, and on top, I have lots of room. Does this make any sense to anyone? If so, do you think I will loose lots of heat from these four spots that will measure about one square foot each?
I'm making the enclosure of used red bricks. When I drew the plans I figured the bricks would insulate. After checking out this forum for about a week, I realize that this might not be so.
Any advice?
Thanks,
Dusty as h*#$ in Sac.

[asudavew]

Re: Insulation information

So when your dome is finished, and after you lay your red-brick enclosure,you will only have 1" left at the very bottom for perlite/vermiculite. But just on the four middles of your sides and back.

If I'm reading you right Me being me, I would probably just go for it... But others will disagree.

I can think of a couple options.. Make your dome smaller, which I wouldn't do.

Or maybe in the thin areas you could cut the bricks lengthwise just in those spots. You know? That would put you up to 3 inches iof space in those areas. One inch of thermal blanket and a couple inches of perlite/vermiculite, or better yet... Maybe 3 inches of blankets in those spots. That would be even more beneficial!

I hope this helps.

[dusty]

Re: Insulation information

Thank Dave- as that was what I wanted to hear. I don't really want to make the oven smaller, and cutting the bricks lengh-wise is very doable. What is this "insulating blanket" I keep reading about? Is this something I can aquire locally or from the forno bravo store?

Dusty

[james]

Re: Insulation information

Hey Dusty,

Welcome to the great central valley. I grew up in Modesto. Maybe not as dusty, but definitely hot as....

I think leaving yourself only 1" at the top enclosure edges might be a little too tight. You could wrap the oven with 1" of insulfrax from the FB Store, but that won't keep some heat from escaping into your enclosure. It might get pretty hot at that spot.

As you are building your oven from scratch, you could either make a little smaller -- or as Dave says, make the walls a little thinner. That way you can fully insulate it, and still have a lot of roomfor cooking. Your 42" oven is plenty big, so you should try to address insulating those spots.

What do you think?
James

[Acoma]

Re: Insulation information

Dusty, give a photo of area around the hearth. I would think that added area for insulation is key here. You can create added area around hearth by reenforcement. Some advice will happen shortly, but get a photo up for diagnostics.

[Unofornaio]

Re: Insulation information

Welcome


That is, on the four sides of my dome, where it touches my enclosure, I only have room for 1" of insulation.

> In this area you can always cut your bricks in half lengthwise or 3/4 to get what you need. This will give you an extra 2" (+ or -) If you use the blanket I think you should be fine as it is. I don't have any experience with it but it sounds as though many are very happy with it and its only what 1"?
If you do cut the bricks in half depending on your design you will only need a few courses until the dome curves and your gap increases, you should parge the back of these cut bricks with mortar. Spread a thin layer over the bricks kind like stucco but just thick enough to coat everything. This will add a bit of strength that you will loose in size. Or you can lay in pieces of stucco corner bead in this area of what 3 or so bricks that are encroaching on the dome. Put down your bed joint press the corner piece in the mortar, with the "L" facing down over the back of the brick then lay your brick. Be sure to keep the metal back about a 1/4" from the edge of the brick so it is not exposed when you rake the joints. They do make brick ladders but they are for full brick and you really do not need them for this. The corner bead is a couple of bucks and 2 10'ers should do you for this or maybe only 1. Start out with the maximum cut at the bottom and then decrease the cut as the gap increases (as you get higher up and the dome curves in) eventually returning to full brick.

I replied to the other post earlier but I will delete it so there are not 2 threads with the same question. You should also probably delete yours.

[DrakeRemoray]

Re: Insulation information

My vote would be to make the oven smaller and insulate properly. That is how I ended up with a 38" oven. It retains heat like crazy, heats up quickly, and never gets hot on the outside...I only had room for about 3" on each side, and put 2" of the ceramic blanket on each side and 1" of vermiculite. I got my blanket locally, but you can buy it from Forno Bravo as well. 1 50' roll was enough (more than) to cover the oven in 2" of insulation.

You said you set the floor already, did you insulate under the floor? That is important too...

Anyway, I am really happy with the size of my oven, plenty of room...

Good luck and keep asking questions...

Drake

[jwnorris]

Re: Insulation information

An inch or so will not jeopardize the function of your oven near as much as inadequate insulation. The key word here is insulation.

J W

[asudavew]

Re: Insulation information

That is how I ended up with a 38" oven. It retains heat like crazy, heats up quickly, and never gets hot on the outside...I only had room for about 3" on each side, and put 2" of the ceramic blanket on each side and 1" of vermiculite.
Drake

Drake,

I like the idea of only 3" inches of insulation. But I am curious about your outside temps, because I will soon be at the outside insulating stage. How hot does your dome get on the outside?

Thanks a bunch!

[dusty]

Re: Insulation information

Just wanted to thank you guys again for all the insulation info. I am now ready to roll again. I've decided to incorperate a few of the ideas instead of any one.
I'm definatly using Uno and Daves idea of making the enclosure wall thinner in those four spots. This will give me 2 more inches for insulation. Drake and James convinced me that insisting on a 42" oven isn't that important. A bit smaller one would be just fine. I decided to go 40" which will give me 1" more for a total of four. My original plan was to use no insulating blanket but now that I know what one is, (thanks Drew), I think I will try to hunt one down.
Is the blanket highly recomended or does the loose vermiculite alone tend to be fine?
Thanks again,
Dusty

[Les]

Re: Insulation information

Dusty,

Go with the blanket, If I remeber correctly, it has 3 - 4 times the insulating factor of vermiculite.

Les...

[dusty]

Re: Insulation information

Les,
That is what I don't get yet. Does that mean a 1" blanket equals 3 to 4" of vermiculite? 'Cause I could add 6 or more iches of vermiculite on the top and corners. Or do you tend to need both?
Dusty

[Unofornaio]

Re: Insulation information

I think you cant go wrong if you use the blanket and fill the rest with vermiculite..I mean you do reach a point in any insulation scenario where too much insulation just doesn't do more for you, but if your enclosure is that tight, at 20.00 and bag you are going to use what 2 bags?..I say why not just add it... I wonder if anyone has any statistics on the temps on the outside of the blanket at full heat..that would be nice to know. Then again this all depends on your anticipated usage of the oven you may not need reach maximum insulation capacity for what you are going to use the oven for.

[wlively]

Re: Insulation information

I I wonder if anyone has any statistics on the temps on the outside of the blanket at full heat..that would be nice to know.

Hey, I found one. Well for Isofrax you can find a data table that gives hot face/cold face values. Unfortunately they give no k values for there products so that doesn't help. They list no table for the Insulfrax, but they do list Insulfrax paper and Isofrax paper and the Isofrax has a lower k value.
At 1202 deg F the cold face is;
343 with 1"
248 with 2"
182 with 4"

Reference:
http://www.unifrax.com/prodinfo.nsf/By+Trade+Name/AED3824C5972AB1885256EDA006F2643/$File/Form%20C-1452%20Isofrax%20Blanket.pdf

[dusty]

Re: Insulation information

OK Acoma,
I, with the help of my son, have downloaded the pics to "my pictures" and into a folder labled "oven photos". I await my next instruction. I'm learning all kinds of things since joining!
Dusty