insulation - classic hearth

[jengineer]

CanukJim has sent me a few photos of the extra insulation he added under his hearth to the vermiculite/concrete layer. You might want to do this if you find that your initial insulating isulating layer is getting warm. That means the heat from your fire in conducting down through the fire bricks, like it is supposed to do, through the thermal reinfoced mass and is not being stopped by the insulating layer.

I have not received the actual words but here is my stab. Jim found some left over insulating facing boards one is exterior Styrofoam that has an R value of 6.8 at 1 inch. You generally stuff your attic with R-13 or better. You will also see mastic (glue) and glue faced foil. Another picture shows A P Foil Faced Foam Sheathing. He has attached the board to the underside of his insulating layer.

[jengineer]

why more insulation

Little slow on this one.

I am not sure if i was clear on this, using the byline of classic construction for a bread oven. Classic oven from cooking floor down is firebrick, thick refactory concrete with refinforcing rebar below and at the very bottom the insulating vermiculite concrete mix.

The purpose of the inulating layer in any oven is to stop the migration of heat from the mass to the outside environment. If you are cooking in the winter and you feel heat coming from the bottom of the oven then you do not have enough insulation. For the Pompeii design with the insulation and the reinforced concrete (no refactory mixed in) in reversed order on the floor there is not much that can be done, if you insulate then you have somewhat made your concrete layer a thermal mass, not a big problem as you want to stop the migration out and get it to return to the core of the oven.

So what does this mean in terms of the oven. I think the fire from the oven, cooking bread not pizza so the fire needs to be pulled, was taken out around 3pm on Saturday. I/we did not journal the times the door was open too much other fun going on. About a dozen Boules were put in for one bake, another 6 baquette's were baked. The boules were pulled and probed to determine core temperature. Some were thrown back in. Bread was rotated as bread in the center is a bit cooler. I believe the oven temp was about 350 to 375. The total oven was nowhere near equalbrium though, the dome mass and floor mass were still out of whack. I could see a masters thesis using one of these ovens and some Algor Heat CFD software to validate time to fire to time to cook and time for equilibirum. And then the oven was opened for guests to see the inside.

The door to your oven needs to stay in place as you do not want to thermal shock your oven, reduce the risk of cracking your fire brick.

So the next day, about 24 hours later, we needed to warm up some prepared food for dinner instead of heating up the house with the gas oven we threw the wife's Jambolaya into the brick oven for a spell. Oven temp was about 285.

When we left Monday afternoon (about 1pm) the oven was hanging around 220.

So. If you touch the outside of your oven and it feels warm add more insulation.

je