Sheep's Wool as Insulation?

[scott123]

Anyone ever try this? I've got a few old wool blankets hanging around.

From the research that I've done, wool has an ignition temp around 1100 F. I'm thinking about placing it underneath the hearth, with an extra layer of firebrick in between. I also plan on running my oven at lower temps- most likely 700 peak for the hearth (a kind of outdoor NY style pizza oven), so I highly doubt the wool blanket will hit anywhere above 600. My goal is use the wool as a barrier between the 600 deg. firebrick and a wood table underneath.

In addition to my lower operating temps, I'm also planning on shorter operating times, so that 600 deg heat won't be sustained for long.

[texassourdough]

Re: Sheep's Wool as Insulation?

My quick research supports your estimate (mine said 600 degrees C) for the ignition point.

While you can probably get away with it, I think you are asking for trouble.

WRT shorter burn times and lower temps, you are going to want/need to heat the surface to at least 750 to clear the oven or you will accumulate tars that will eventually lead to a fire in the oven. While the needed heating time is a function of wall thickness and one can make the heating time shorter by making the wall thickness thinner, you can't reasonably take a given oven and shorten the heating time much from that needed and get good results for if you haven't heat loaded the refractory your oven temp will not be stable and will rapidly decline.

There is no problem running an oven at lower temps but assuming you build a Pompei (or any other oven) the heating time will need to stay pretty close to the norm. You will simply end up with a smaller fire and (most likely) a slightly longer wait between clearing the hearth and beginning baking. Your wood and time savings would be minimal.

Good luck!
Jay

[Food With Legs]

Re: Sheep's Wool as Insulation?

Scott,

I'm sure you've taken this into account but remember that a wood-fired oven doesn't have a temperature knob or an off switch so once you get the thing built you may find that it's hard to implement your plans for controlling the operating temperature and time.

As well as the flammability issues I'd also be concerned about the load-bearing strength of the wood table you envision as a base.

It sounds like what you're after is an oven built in the low-cost, found-object style. I don't think there is anything at all wrong with this but you might have more luck by trending towards the cobb style of oven. I think there was a post on Slice about one of these built for under $100 or so.

Cheers,
-David.

[scott123]

Re: Sheep's Wool as Insulation?

WRT shorter burn times and lower temps, you are going to want/need to heat the surface to at least 750 to clear the oven or you will accumulate tars that will eventually lead to a fire in the oven.

Hmmmm... that hadn't occurred to me. That's good to know.

What about if I heat the oven with lump charcoal? That should create less tars, right?

As well as the flammability issues I'd also be concerned about the load-bearing strength of the wood table you envision as a base.

My oven, as I'm envisioning it, should weigh about 120 pounds. I weigh a little more than 250 and can sit on the table without any problem. The wood gives me portability.

The oven I'm putting together isn't exactly a frankenwebber, but it's in that general direction.

And, yes, there is no temperature knob. I do plan on testing the heck out of this and being extremely careful with my fuel quantities. My target hearth temp is 550. I'm only taking it to 600-750 so the stone can have a bit of a cooling period and the heat can even out a bit. Using charcoal, I don't think hitting that 150 degree window will be easy, but I don't think it's impossible.

[texassourdough]

Re: Sheep's Wool as Insulation?

Hi Scott!

You may want to consider that wool has lanolin on it and lanolin ignites at about 830. Still well under your target but...

Charcoal can heat the oven but...I think you underestimate how much heat you need to generate to get the oven hot. Most of it goes out the chimney. It is my impression that the best fuels for heating an oven involve bright, hot flames. While you may be able to heat your lightweight oven with charcoal I think you will find yourself having to use wood. How about putting some "safer" insulation on top of the wool. Even another layer of bricks would help.

I think you really need to plan to reach 750 to clear the dome. With a lightweight oven taken to 750 it will probably drop pretty quickly to 550 if you simply clear the hearth and build a small maintenance fire as soon as the dome clears. The refractory will not be very charged so it will keep sucking heat and bring down the surfact temps pretty quickly.

Good Luck!
Jay