Insulation Advice

[Frasu]

Hi, I have purchased a woodfired oven Kit made from high density castable refractory concrete. The kit comes with a 1 inch Fire Blanket for the floor and a 1 inch fire blanket for insulating the dome.

The manufacturer swears black and blue that this is enough insulation and I have seen heaps of pictures of completed ones.

What are your thoughts?

Basically if i follow the instructions i will be doing a concrete slab with a fire blanket and then laying the floor on top of this.

I will be covering the dome in a 1 inch fire blanket (chicken wire, alfoil etc) and then rendering it.

Is this enough insulation? What do yo recommend?

Many Thanks. This is a brilliant forum.

[DimTex]

Re: Insulation Advice

I find it hard to believe 1 inch of anything is enough unless the actual dome itself is very thick. I built my dome according to the plans on this site, that produced a dome with a wall thickness of about 4.5 inches, I added 4 layers of the FB blanket and my stucco exterior has never gotten much above outside ambient air temperature. Fact is, more insulation means better warm up and longer sustained/retained heat which means it requires less fuel.

[dmun]

Re: Insulation Advice

I'm particularly concerned about the "blanket" under the floor. I suspect it will compress and loose all insulation value. We use a rigid insulation, either four inches of vermiculite concrete or two inches of rigid refractory board under the floor.

As DimTex says, an inch of anything isn't enough. You'll have trouble getting it up to temperature, and keeping it there. I suspect that your vendor is trying to save money at your expense: Refractory insulation is very expensive, particularly down under. I wonder what other ways he's saving money?

[Frasu]

Re: Insulation Advice

Thanks guys, this is what I suspected. I am making provisions and buying insulation bricks for the floor. They are 63mm thick and are apparently better than using vermiculite or hebel. At $1.80AU each brick they better be.

I have ordered a roll of fire blanket which will give me 3-4 inch of blanket around the outside of the oven.

This will add about $250AU to the cost of the project.

I have spoken to others who use this oven and they have said it works perfectly but the oven is roaring hot all over and cant be touched and they go through loads of wood for each cooking session.

Hopefully the extra insulation will alleviate this issue.

[james]

Re: Insulation Advice

I want to second the advice to not use the blanket under the floor. I have seen that technique, and as you have noted -- the outside and bottom of the oven get hotter than heck when you are cooking. That isn't good for making pizza, wood consumption, or retained heat roasting and baking -- or for your neighbor who burns his hand.

Insulating firebrick below is OK, and 3-4" of blanket on top is the way to go. You will be glad you did it.

James