Do I have a heat sink issue? Not heating long enough?

[gregwrockwell]

I'm late to the game here, but trying to figure some things out.

We built this oven 7 years ago and have used it consistently ever since. The base under the firebrick is 6" of vermiculite concrete. The floor and dome were all done with firebrick and appropriate mortar. We put on a fiberglass blanket then another 3-4" of vermiculite concrete on the outside of the dome before finishing with stucco.

I could post photos now and you would see the whole thing is under a patio cover with the chimney going up through the cover. The oven is never really exposed to rain or snow.

The oven has a 30" interior floor. I've got enough room for a fire banked to the right and two pizzas next to it, front to back. I turn them a little then bring the back pizza to the front and vice versa.

All these years I've used Peter Reinhart's pizza dough recipe from Artisan Breads Every Day with a couple of minor modifications that I liked. I recently switched to Vito Iacopelli's napolitano pre-ferment recipe with a 48 hour two stage fermentation. Life changing. And I am a giant Peter Reinhart fan.

So, with the reduced sugar and oil in my dough I can cook at a much higher temp and I started to get more serious about 750-900 temps for cooking so I can get the leopard spotting and "soft & crunchy" thing.

I hadn't used an IR gun in years, so I went and got a new one. I typically run a pretty big fire for an hour or 90 minutes and then bank the fire and start cooking.

What I noticed in attempting to keep the higher temp is I'm just adding wood constantly. That's not soooo bad, but I've got a big pile of ember and ash as things move along.

I decided to investigate gas heat sources and bought a pipe burner from Tejas Smokers set up for high pressure propane. The thinking is with a potential 150K BTU output, I should be able to get the oven temp really high and have no ash and embers to worry about and not have to keep loading in wood.

So, the other night I tried my first cook with that and I could not get the oven temp up to anything close to what I want. It was like 550-600.

I know I'm not losing any heat through the dome. It literally registers no heat change ever no matter how big the fire is. I'm wondering if my 6" base is not as insulating as I wish. I haven't tried gunning the dur-roc board to see if it changes. If it's acting as a heat sink instead of an insulator it's a big mass.

And finally, maybe I just have never taken the time to saturate the masonry as seriously as I ought to. I used to build a roaring blaze for 45 minutes before cooking. In the last year I started building the fire for longer.

I would love to just have the propane work, either as the supplement after the fire has really gotten the oven hot (haven't tried that yet), or better, on its own when I don't want to deal with coals/embers/ash.

Interested in the community's thoughts on order of troubleshooting and ways to test different hypotheses.

[UtahBeehiver]

What was the ratio of the vcrete under the fire bricks? The symptoms seem to indicate wet floor insulations but being under a deck cover does not lend itself to water ingress unless it is coming from around the chimney or sideways/ By the pics, the vcrete under the floor looks very rich in portland. Attached in a K value chart showing various vcrete ratios, with 5 to 1 under the floor and 8-10 to 1 on the dome recommended. If a rich vcrete insulation (ie 3 to 1 or includes sand) under the floor and the dome wall this is a possible heat sink and is especially negatively affected it there is water present in the mix. Where in SLC are you?

[gregwrockwell]

We're a couple blocks off of 9th and 9th. Pleased to meet you. Where are you?

There is for sure no water ingress. But I don't have a good way of knowing what the ratio was on the concrete at this point. I was thinking about getting a little concrete coring saw and drilling underneath, from the wood box, to get a hunk of concrete and measure its density, but I don't know if it justifies the effort. I could also gun the underside when I've got a big fire going and see if it registers. That feels scientific, but I'm not sure if it really qualifies.

[UtahBeehiver]

Taking a temp from the underneath will give you an idea if you are losing heat from the heath. But you have a very thick what looks like a two layer hearth, standard concrete plus an unknown ratio vcrete, I am located in the Aves. I am sending you a PM.

[gregwrockwell]

An update: I did a pizza cook this weekend with 2+ hours of wood fire to pre-heat the oven and then banked the fire and put in the propane burner to maintain heat while cooking.

1. I IR gunned the cement board underneath the base of the oven before starting the fire and then again as I was ready to start cooking. The temp moved up by 10* F during that time. I think that confirms the suspicion that my base is acting as a heat sink, rather than insulation. Unfortunately, it's a BIG heat sync. 6" thick. About 6' x 5'.
2. The propane after wood method worked quite well. I didn't load in any more wood. And the temp stayed pretty high. Not quite as high at the end as I would like. But definitely functional.

Now I'm contemplating:

Do I want to mess with this? I've baked 1000+ pies in this oven and been very happy with it over the years. Even with the heat loss, I've got a pretty great setup.

If I do start to mess with it, it seems like the viable option is to start from the floor of the oven. Pry out fire brick and put in fiberglass panels and then put in a new floor? Just lay fiberglass over the fire brick and put in 1" thick hearth stone on top? That would reduce my oven height, which doesn't seem like the worst thing.