Heat retention improvement ideas

[Stlhdmn]

I have a WFO and I'm quite happy with the output, however after two maybe three pizzas the floor does not retain the heat as well as I would hope.

My floor is made from the bottom up with: 1. 3/4" plywood, 3 in of sand, 1 sheet of cement board, and then standard fire bricks. The insulation under the floor seems okay because the bottom of the floor under the stand does never exceed 100°...

Nevertheless I want to know how I can improve upon this. I know that my oven does not retain heat well overnight cuz in the morning it's usually around 100 degrees after an early evening pizza burn...

When I cook I generally get the floor up to 700° or more, but as I've said after the third pizza the floor cools quickly. Is this a matter of the kind of brick that I'm using? The fire brick I am using is from Menards and comes in a box of six, it is more porous than some of the smooth brick that I've seen.. could this be a culprit to the floor?

I would appreciate any suggestions y'all will have to improve the heat retention. I am open to residing it or refacing the outside to improve it, that should not be a problem but before I do anything I would like to get some input.

Thank you in advance!

[UtahBeehiver]

A couple things, sand and cement board ( I am assuming something like Durorock) and not thermally effective and act as a heat sink. Are the fire bricks full thickness, ie 2.5" or splits 1.25" if splits, there is not enough thermal mass to retain heat in them to cook multiple pizzas, finally, any chance the sand under the bricks are wet at all, this make the heat sink even more pronounced. What is the insulation on the dome and how much?

[Stlhdmn]

The walls/ceiling are about 3.5 to 4" thick, refractory cement.

[UtahBeehiver]

Floor splits or full size? What is the dome insulation over refractory?

[Stlhdmn]

The floor is fire brick. The ceiling is very well insulated, the top does not get hot. It's the floor that cools faster...

I am thinking of:
1. Line the floor with
a. Another layer of brick
Or
B. Unglazed quarry tile
Or
C. A pizza stone..

Suggestions?

[Petter]

Sorry to say, but you don't have any insulation in the floor. Only different types of mass. The reason you don't get above 100 C is because you have not saturated the floor mass with heat. Take out the firebricks, scoop out the sand and re-fill with vermiculite/perlite concrete or CaSi-board. Put the firebricks back.

[Chach]

Sorry to say, but you don't have any insulation in the floor. Only different types of mass. The reason you don't get above 100 C is because you have not saturated the floor mass with heat. Take out the firebricks, scoop out the sand and re-fill with vermiculite/perlite concrete or CaSi-board. Put the firebricks back.

I agree with the above you have enough room to put 4" of calsil board. just bring it up the difference with a sand clay 50/50 mix for the other 1/4" I'm assuming you have 1/2" cement board. The only problem I see is your dome walls. What are the walls sitting on? If its on the structural slab that is not good as your heat is wicking out through the slab and you will not be able to get insulation under that but if the walls are on top of the mixture of wood sand and cement board taking these items out may disrupt the foundation of the dome walls and create major problems as your sand base will start to shift unless you can take it out a little at a time and slide calsil board underneath in sections and if there's a gap tuck point refractory mortar or homebrew using a masons back filler to close the gap between the brick and the calsil board and create stable support for your walls if your dome is on that plywood sand and cement board base. This is risky but doable if a little at a time is done but not in super small pieces.


Ricky

[Fishman]

The fire brick I am using is from Menards and comes in a box of six, it is more porous than some of the smooth brick that I've seen.. could this be a culprit to the floor?

I am new, and certainly no expert... but this caught my attention. Aren't these insulating fire bricks, and not the dense fire bricks. If so, isn't this the problem right here?

[Stlhdmn]

I'm going to replace the floor best I can using the thicker fire brick. I'll maybe be able to put fire blanked down under too... I'll post my outcome...

[david s]

Fire blanket will compress under the weight of the floor brick, you’re better with an insulation board of at least 100 psi strength or cast your own 5:1 Vermicrete. Your floor bricks need to be dense firebrick and should weigh at least if not more than a standard solid housebrick. If they’re really light then they are insulating firebricks with little thermal mass. A plywood base is a bad material on which to build an oven, mainly because trapped underfloor. moisture will kill it long before the floor or dome cease to function like new. It’s probably not possible to replace it without a total tear down so you have what you have.

[Geordy05]

I'm just learning but have been researching foam glass. Would that be a good option for efficiency or does it give the most benefit with board on top then bricks to not exceed the 900F temp?