Old 05-10-2013, 04:20 AM
plootsnot's Avatar
Join Date: Apr 2009
Location: Holland
Posts: 26
Default Heat loss thru substucture


Wondering if my oven losses heat thru substructure? If I feel the roof of the wood storage onder the oven it is warm after a few hours of burning. I have about 6 inches of insulation (portland+verm), thin layer of fireclay and then the fishpattern of full firebicks for floor. Anybody else notice this with their oven?

I have no door yet so not sure long it would stay warm with a door. Next morning after firing its warm in the oven but not crazy hot, probrably 80 -120 celcius.

Thanks for your input!
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Old 05-10-2013, 06:27 AM
mrchipster's Avatar
Il Pizzaiolo
Join Date: Apr 2010
Location: Minneapolis, MN USA
Posts: 1,478
Default Re: Heat loss thru substucture

After a long fire with pizza temps in the 850f range my wood bin ceiling will be about 110f with a temp of 50f for the air.

I have 2.5" 7-1 vermicrete with 2" FB board. My slab is 4 inches of concrete.

Yes, I do wish I had more insulation under my oven floor.

Right now my oven is 420 inside, 2 days after fire, after baking bread yesterday, and the outside temp is 32f the ceiling of the wood bin is 75f.

I do have a 4" thick insulated door and the Oven will still be over 200f after 5 days with outside temps averaging 35f.

One other thing, if your oven is still new you may have water in your floor insulation that has not burned out yet. Give it time and more fires and it will dry out. ( I just looked at your postings and see that your oven has been complete for some time is it possible that water is getting into the floor insulation?)

Build a nice door and heat loss will go down lots. My door is described in my Chips 42 in Minnesota posting.


Last edited by mrchipster; 05-10-2013 at 06:51 AM.
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Old 05-10-2013, 07:17 AM
Il Pizzaiolo
Join Date: Nov 2006
Location: San Antonio
Posts: 1,719
Default Re: Heat loss thru substucture

Your hearth base sounds much like mine - an Alan Scott barrel vault base. Without the insulation boards as FB encourages your hearth will leak much faster. It is not a big problem unless you want to braise or roast meat the second day. You will likely experience that pizzas will cool your hearth and you will want to rake coals out to recharge the hearth every half hour or 45 minutes - or keep a larger than normal fire. Irritating but not unusual nor a real problem - just takes attention.

The reason your oven is cold the next day now is not the hearth - it is the lack of a door. My oven is around 375 the morning after pizza.

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Old 05-10-2013, 07:29 AM
Master Builder
Join Date: Oct 2012
Location: Los Angeles
Posts: 732
Default Re: Heat loss thru substucture

And if you dont have a door in the meantime you can cover the entrance with bricks. This is a temporary bandage till you make the door.
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Old 05-10-2013, 08:55 AM
plootsnot's Avatar
Join Date: Apr 2009
Location: Holland
Posts: 26
Default Re: Heat loss thru substucture

Thanks Jay and Chip,

Jay what you described about raking coals back over is what we have found out as well, human nature I guess! Great minds think alike wish only I had better insulated the floor. Will try a temp door to see how that goes, planning to fabricate something permanent soon.

Haven't been on here for years will have to update my photo and build information. Oven is almost done after 5 years!!! Work in progress kind of thing...

Best regards,


Last edited by plootsnot; 05-10-2013 at 08:58 AM.
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