Is it possible to over-insulate dome and hearth?

[fegerter]

Where does the law of diminishing returns kick in?

[UtahBeehiver]

That is too difficult to generalize. It depends on type of insulation(s) used. How the oven is designed and used, etc.

[JRPizza]

If all you are going to do is heat your oven, cook a pizza, and not mind if the oven is cold in the morning, using more than minimal insulation a waste of money. If you want to do retained heat cooking the day(s) after firing your oven the importance of insulation goes up. Even if fuel is free, constantly firing the oven and trying to maintain a consistent temperature requires a well insulated oven. If you want to cook with retained heat I recommend reading up what others on the forum have used and how their ovens are performing. I used 5" of CF board under the floor of my oven, but considered 3" the minimum. 5" worked out as I bought two layers @2.5 inches and got the best cost per inch I could find. I used 3" of CF blanket on the dome. Made pizza last night and fired for another half hour after that. My dome was 500 this morning (~15 hours later) and we are going to cook up a chicken, follow that with a beef roast and a bunch of vegetables, and then a small pork roast. We often cook for the week with one firing. It's all about finding the right balance of thermal mass and insulation.

[Gulf]

I think this has been covered very well. However, (I will add) when she says something like "this thing is going to cost more than my she shed", you've probably found where the law of diminishing returns has kicked in .

[fegerter]

Thanks for the replies and links to your build pages!

[RandyJ]

There is no maximum amount. But once you cross 4 to 5 inches of calsil under the oven and 3 to 4 inches of ceramic blanket over the top. If you want more you can cover the whole oven in loose vermiculite and increase the insulation value. But after this the next best option is to install heat breaks and keep the outer arch from becoming a heat sink for the rest of the dome. All it takes is 1/4" gap and then stuff with ceramic roap and seal with a refractory calkon the inside and pack with vermicreete on the outside. For heat retention that will do you more good that excessive amounts of insulation.