Question about oven floor insulation

[Puma559]

I may have made a big mistake on my oven. I've been reading about insulating the bottom of ovens and have seen many people say that sand is a horrible insulator. Well, I'm almost finished with my oven and I used sand under my fire brick floor. Now I'm freaking out because I'm going to be losing a lot of heat through the floor. My oven is 36 inch diameter with a dome height of 17 inches and a 18x12 opening. My floor is fire brick with half inch of sand and a 5 inch concrete slab. Am I going to lose a lot of heat? Will the concrete help keep the heat in? I plan on using the oven for making pizzas, bread, roasts and pretty much everything else.

[ATK406]

Re: Question about oven floor insulation

Yes, you will lose alot of heat through the sand and into the concrete slab. Unfortunately, there isn't much you can do about it now (not easily anyway). I'm assuming you built a brick oven - not a preassembled kit.

If I were you, I would insulate the @#%& out of the dome to ensure that you keep as much heat in the rest of the oven as you can. If it is not too late, you might consider a layer of refractory cement or homebrew (not a beer ) over the dome to provide additional thermal mass to compensate for the heat loss through the floor.

Cooking pizza probably won't be too bad since you should have lots of heat on the surface of your bricks and a fire going on the side anyway. Roasts and BBQ will probably be ok too (as long as you can keep enough heat in the rest of the oven or a small fire or coals burning on the side). Bread may be the biggest challenge as you generally cook with retained heat and as you wait for your oven to equalize (dome and hearth coming to the same temperature (@ 400 - 500 F) you will rapidly lose heat from your floor to your concrete slab. It may not be too bad, you won't know until you try it (unless you have alot of experience with thermodynamics).

One more thought; If you find that your hearth is cooling too fast to equalize with the dome, you could keep a half dozen fire bricks (full or splits) in the oven while you are cooking pizza (to store heat) and when it's time for bread arrange these bricks to form a "new" floor and cook your bread on top of them (they may be hotter than your floor because they have not been dumping heat directly to your slab). This might be awkward at first (or unnecessary) but with practice it might work ok.

In the meantime, buy alot of wood.

Regards,
AT

[Puma559]

Re: Question about oven floor insulation

Thanks for the reply. I really wish I would have found this forum before I started me oven. I think I can still pull the brick out of the hearth because I didn't mortar them. I'm thinking of putting down a one inch thick insulation board on top of the concrete and laying fire brick on top of the board. Do you think that would work? It will raise my oven floor about an inch giving me a 16 inch dome height. As for the dome I have fire brick and a layer of clay brick on top. Is that enough or should I add a layer of plaster on top of brick.

[ATK406]

Re: Question about oven floor insulation

If you are willing to raise the floor, get rid of the sand while you are at it (if you can) and put down two inches of insulation. That would certainly help. I don't know if you can find it at the thickness you want or if you'll have to cut it (be extra careful cutting it and dealing with the dust - nasty stuff).

If you're already to fire it up, I'd test it out to see how it works (after curing of course). You may be suprised and happy with the results. It sounds like you could go back and raise the floor later if you want.

Maybe some pictures would help us understand what you are dealing with...you know we're all oven junkies on this site....we love the pictures.

Regards,
AT

[stonecutter]

Re: Question about oven floor insulation

Is there any reason you couldn't at least remove the center of the floor, then use proper insulation?

[Les]

Re: Question about oven floor insulation

As for the dome I have fire brick and a layer of clay brick on top.

While you are working the floor I would pull the clay brick (if possible) and add insulation. The fire brick will give you enough mass - now you need to retain the heat.

Just curious - where did you get these plans?

[Puma559]

Re: Question about oven floor insulation

I watched a couple videos on YouTube. I wish I wouls have found this forum before I started. I'm afraid of damaging the dome if pull the clay brick off. All I need is 2 more rows to complete the clay brick. Can I insulate over the clay brick? If I leave it as is then that means I'm going to be losing heat from done and floor. That sucks bad long as I can cook pizza and roast stuff I'll be happy.

[Puma559]

Re: Question about oven floor insulation

Is there any reason you couldn't at least remove the center of the floor, then use proper insulation?

Yah I can do that. The bricks are lose with no mortar. It would just raise the floor about an inch and give me a dome height of 15-16 inches. Is that too short of a dome?

[Les]

Re: Question about oven floor insulation

Can I insulate over the clay brick?

Yes you can - it will require more fuel to heat but the heat will stay longer - not a bad trade. In regard to the height, I did a quick google and found someone claiming the ideal height to be the diameter divided by 3.4. For your 36 inch that means a height of 10.6 inches. This is obviously for a pizza oven but there is no reason you couldn't bake in it if the heat is there.

[Puma559]

Re: Question about oven floor insulation

Yes you can - it will require more fuel to heat but the heat will stay longer - not a bad trade. In regard to the height, I did a quick google and found someone claiming the ideal height to be the diameter divided by 3.4. For your 36 inch that means a height of 10.6 inches. This is obviously for a pizza oven but there is no reason you couldn't bake in it if the heat is there.

Thanks for looking that up. I feel a little better knowing i don't have to tear down the top brick.

[stonecutter]

Re: Question about oven floor insulation

I think I can still pull the brick out of the hearth because I didn't mortar them. I'm thinking of putting down a one inch thick insulation board on top of the concrete and laying fire brick on top of the board. Do you think that would work?

Yes, it will work...use splits, as mentioned before.

Yah I can do that. The bricks are lose with no mortar. It would just raise the floor about an inch and give me a dome height of 15-16 inches. Is that too short of a dome?

If you built a Neapolitan (low dome) oven, that should be fine too.

[Laurentius]

Re: Question about oven floor insulation

Hi Puma,

Stop working on the oven, and put up some photos of your construction. Its better to make corrections at this point, than finishing something that be a disappointment forever.
Counting to 10 and allow the panic to subside, it will be alright in the end.

[Bacterium]

Re: Question about oven floor insulation

Puma559........my first oven was a pretty similar experience to yours - its under a thread. You will most likely get up to good temp and do nice pizza. It's the retained heat the next day where the biggest loss is. I found in comparison to others here you end up having to do pizza and bread in the one days firing, as opposed to a lot of bottom insulated ovens and can do successive loads here they can't really do bread until the next day. This is assuming pizza temps the night prior.


Doing what has been suggested so far will def. bring benefit and worth the effort.

[Puma559]

Re: Question about oven floor insulation

As long as I can make pizza and roast different meats I'm happy with that. I'm going to test it out and see how it works. I can easily pull the hearth bricks out and add the insulation.

[wotavidone]

Re: Question about oven floor insulation

Mate, you should be good to go. I take it from your description that the floor bricks are inside the dome walls. If this is the case, you just pull the bricks out, add some insulation, and put them back in. For example, if you added two inches of insulation, then your internal dome height would become 15 inches, and your opening height becomes 10 inches.
This brings the oven opening ratio down from 12/17=0.71 to 10/15 = 0.67.
Since most people reckon it should be 0.63 plus or minus a bit, this is good.
I have a 9.6 inch opening, I would not want it to be any lower than that, but 10 inches should be fine.
Then just insulate the heck out of the dome. It will work fine.