Combo Pizza Oven / Fireplace Build

[kew71]

My wife and I are starting a combo pizza oven / fireplace build. We plan to build a 32x36 barrel oven with the oven on top and fireplace down below. On either side will be concrete counters with wood storage below (although considering a wood fired grill on one side). We will use reclaimed brick to face the oven and hide the block. Not sure if we will clad the outer insulating layers of the barrel with brick or box it all in and use a traditional roof to cover it. The slab is done. The center where the oven and fireplace will be is 6 inches thick with lots of rebar.
We have a couple of questions.

For the hearth. I was looking at options. Either a solid concrete top with the perlite mix poured on top of that or pour the perlite mix in a square and then pour the concrete around it. Thoughts on best way to go? Should the perlite hearth mix have a concrete layer on topIdeally we would like the perlite mix to be 4-6 inches thick.

We are trying to figure out the flue for the fireplace. We have seen several options. We are considering two. One has the fireplace split the flue around the oven chimney. The other has two removable firebricks in the entrance to the oven and the fireplace flue uses the oven chimney and you have an outer door you can install in the oven entrance. Thoughts on design?We do not want to separate chimneys.

If we went with a traditional roof, would there be any added benefit to cover the barrel and insulating layers with sand for additional insulation?

Thanks.

Kevin

[kew71]

My wife and I are attempting a combo pizza oven / fireplace build. The concept is that there will be a counter on either side of the oven/fireplace with wood storage under those and the fireplace below the pizza oven. The oven/fireplace is placed off the end of the deck. The slab is poured and I reinforced the heck out of it with rebar. We live in northwest FL so no danger of a deep freeze. The slab is 6 inches thick where the oven/fireplace will be. I am going to start laying the block soon. I have a couple questions.

1. I am looking for ideas on how to route the chimney for the fireplace. My initial thought is to have it towards the front and go up through the counter top on either side of the oven chimney. I have also seen some builds that allowed you to remove two bricks from inside the hearth door and allow the fireplace to exhaust up through the oven chimney. It's doubtful we would ever burn both at the same time. Thoughts on the best way.

2. When I pour the counter that the oven will be built on, how thick should the initial counter be? Ideally I plan to use a 4-6 inch thick perlite mixture for the hearth under the oven. Should I recess it into the concrete surround or should I pour a solid counter and pour that on top? We plan to do a 32x36 inch barrel oven.

The outside of the oven will be clad with reclaimed brick to cover the block and oven dome. Not sure yet if we will square it off or use the reclaimed brick to cover the barrel/insulation. Thoughts on that? Also I was thinking - how would it work to cover the barrel and perlite insulation over the barrel with sand if I did square it all off? Would that add additional insulation?

I need to scan and post a drawing I guess.

Any constructive help and thoughts are appreciated.

Kevin

[RandyJ]

There was a person that did what you are talking about several months ago and had the floor of the pizza oven explode from the heat of the fireplace. It is not generally seen as a good idea to stack the two one on top of the other. Side by side would be fine but stacked is asking for problems.

Randy

[kew71]

Was he burning both simultaneously?

[RandyJ]

I do not remember exactly what the details were but the fire in the fireplace caused the concrete slab to expand and steam from within the slab exploded up into the oven chamber. That could always be a problem because the concrete will always sucks water back in if it gets wet then you will have the potential for a steam explosion. Also standard concrete isn't great at taking heat and will start to break down. Also the rebar will expand at a different rate from the concrete and cause more stresses on the structure. So unless less you have a trained engineering team do your planning I think you are in for a lot of trouble because you just changed all the standard variables.

Randy

[dakzaag]

No, the exploding hearth situation had a contractor do the work who did not know what he was doing and used Portland concrete for the oven support, above the fireplace. This is a tough design challenge and some have made it work. I personally think the fireplace vent has to go behind the oven and the oven needs to be squirrel tail design so the two flue's end up at the back of the unit. Every situation has unique parameters so you may find a better design for you location.

This dual appliance concept is not for a beginner, you need some experience in Fireplace design and construction to know what will work and what won't. You could end up with a poorly designed oven that you don't like and a fireplace the dumps smoke out the front opening like a coal train.

Sand is not a good insulator. For an oven stacked up on a fireplace, insulating the floor is almost impossible. Pericrete will not handle the fireplace temperatures. This needs to be a refractory casting, or large refractory tile to span the opening. You basically give up the retained heat aspect of the oven when it is built over a fireplace. If you want to cook with retained heat, then you are probably better off going side by side.

[kew71]

The plan for the fireplace was to have it under the oven entrance, not directly under the oven itself. The fireplace would only be 30 inches deep. Based on the size of the slab poured, I could get away with having a longer 'tunnel' for the oven entrance and it would not be under the oven at all. My concern would be air flow for the oven if I make the 'tunnel' too deep.
Also the fireplace would be lined in fire brick as well.

[dakzaag]

If your fireplace is 30" deep you won't get that much heat out of it because the heat (both convection and radiant) never make it out of the firebox. The best design for outdoor fireplace is a Rumford style which is tall, wide and shallow, like 32" wide and 16" deep. This leads one to think that having flues run up beside the oven vent will work and I have seen this completed, but the builder is perhaps one of the most innovative stove mason's in the world. The risk is smoke leakage because the chimney is right at the front of the firebox and if it doesn't draw nicely, the smoke is already right at the front opening with a lot of momentum taking it out the front. If you don't really care about the heat, then the old TV box design isn't really a problem, but the risk of smoke spillage is a real mood killer no matter who you are.

This also forces the vent for the oven to be longer to some degree. This isn't a problem unless you have short arms, but really the length of your tools will compensate except for really heavy objects like a crock full of chili. The air movement through the vent will work either way because the fire requires air and the heated smoke will go out the vent at the highest point. The laws of physics can accommodate an elongated vent tunnel.

[kew71]

We live in Florida so the fireplace is more for looks than heat since it is outdoors anyways. I actually was going with a shallower fireplace originally but saw other designs. I will re-look the Rumsford type.
I have time to mull it over. Knee surgery so the build is delayed. Thanks

[Gulf]

I second Dakzaag on the Rumford style. I built one (at least it is "Rumfordish") and am very impressed on how it performs. Though, I don't think that I would attempt an "over and under" combination with a WFO. A Rumford style fireplace has some exacting specs for it to work properly. Those are going to be pretty difficult to incorporate with an oven. Having the fireplace separate from the oven whether functional or just as a decoration will allow you to use both at the same time. Crestview, Florida is not very different from my location in MS. Ya'll have some very cool nights in the winter. Fall, Spring, and Winter are my favorite times to entertain outdoors.

My firebox and the face are built out of repurposed lime kiln brick. It is 50" wide, 37" height, and 25" in depth. The fire is started in the very back in a teepee stack. The radiant heat will push folks way back from it. As the chimney heats up the fire bed can be spread out a little further and the coals can be used for cooking without worry of smoke. It is very nice to be able to have both the oven and the fireplace going at the same time. That alows me to have another place for folks to congregate as I am working the oven.