A chimney on the pizza oven is the last functional piece needed before I can make pizza.  It’s kind of like the last piece of the puzzle before you can step back and say, “It’s complete!”.  Except, it’s still only partially complete.  But it’s functionally complete.  That’s good enough for now!

In fact, a chimney isn’t even functionally required for a pizza oven.  If a chimney wasn’t there, the door would serve as the chimney.  Cold air would enter the oven through the bottom of the door while the smoke and hot air would escape out of the top.  But, who wants smoke coming out of the front door when you are trying to make pizza?  Not only would the smoke make it difficult to see and breath, but it would leave black stains all over the front of the oven.

When thinking about putting a chimney onto the pizza oven, there are again a lot of things to think about.  Considering I have never built a chimney, I had to do a lot of research to understand what I was doing.  Some of the questions that I had were:

1. What material do I use for the flue?  Stainless pipe or clay flue?
2. How will I support the base of the chimney?
3. How does the chimney go through the roof without leaking water?
4. What prevents rain from coming into the chimney?
5. Since the chimney will get hot, do I need to insulate or brick around the chimney?  If so, what prevents water from seeping between the flue and the outside brick/insulation?

If you have any experience with chimneys, these questions may seem pretty dumb.  But I knew nothing.  So below is what I found.

Stainless or Clay Flue?

Ultimately, either a stainless pipe or clay flue works the same.  They both exhaust heat out of the oven.  It is the requirements other than the pipe that really make the difference.

First, let’s look at a metal pipe.  The metal pipe must be stainless steel.  A galvanized pipe will rust out from the exhaust fumes.  Also, the metal pipe should be double-walled.  A single wall pipe will get scorching hot and may have an effect on any sealants between the pipe and the roof.  To connect the pipe to arch transition, an anchor plate is needed.  After all is said and done, using a double walled stainless steel flue is expensive.  Here is an example of this double walled stainless flue pipe and anchor plate.  Once the flashing is included, you are looking at >$200 just for the chimney.  Despite the expense, however, a metal pipe is very easy to implement.  You mortar in the anchor plate, attach the pipe, and attach the flashing.  That’s it.

The other option is a clay flue.  Clay flue’s are dirt cheap.  I bought a 2 ft section for less than $10. However, they require a little bit more work.  A clay flue should be surrounded by brick leaving a 1″ air gap between the brick and clay flue.  Still, after including the brick, the cost is ~$30.

Between these two choices, I decided to go with an 8 inch by 8 inch square clay flue.

Chimney Support

As I mentioned above, a metal pipe will require an anchor plate.  For a clay flue, you can mortar the flue directly to the brick.

In either case, a transition will have to be created between the landing arch and the chimney.  To make the transition, I used my angle grinder to cut angles on bricks.  Once mortaring them into place, a flat and level area is created for the chimney flue to rest on.

Mortaring the custom cut bricks into place to transition the curved arch into the chimney.

Front view of the arch/chimney transition

Insulating the chimney

If choosing a metal pipe for a chimney, you should choose an double walled pipe.  For these pipes, there is no need to insulate around the chimney as they are already insulated.   Clay flues require brick to be laid up around the flue with a 1 inch air gap.

How to keep water out of the chimney?

Since I haven’t actually made it to the roof yet, I can only speak to what I have read.  Whenever I get to the point of putting on the roof, I’ll give an update on how I did it.  But, in the meantime…

There are a lot of gaps around the chimney for water to potentially invade.  First, there is the gap between the chimney and the roof.  To prevent water intrusion here, metal flashing is commonly used.  For steel pipe, you can buy these for the right diameter of the pipe.  For a clay pipe, you put the flashing into the brick exterior.  There are tutorials out there for flashing which are pretty helpful.

The other place that water can invade is between the clay flue and the brick.  Since there is an air gap, this could easily allow water to seep down the flue.  To prevent this, a concrete chimney cap is commonly poured in place.  During this pouring process, window seal insulation (the blue foam stuff) is wrapped around the clay flue.  After the concrete cures, the window seal insulation is cut down and the gap filled with high temp silicone sealant.

The clay flue is mortared into place on top of the arch brick transition.

Alright, now that the chimney is in place, I have a working pizza oven!  It may not be protected from all of the elements yet.  It may not look extremely appealing (in fact, a little redneck at this point).  But, it works!  But before firing it up to full temperature, it will need some smaller fires to cure it.  I’ll update you soon on how to cure the oven.

After the oven dome was complete, I felt like I ran into a brick wall. No, this wasn’t from the work of actually building the dome. Instead, it was from the decision making that we had to do after that. You would think that Lara and I would have this grandiose plan on exactly what we wanted this pizza oven to look like. But, we didn’t. All that we knew was we wanted a pizza oven on our patio. Whatever it looks like, it will be fun to cook pizza and entertain guests. We just had so many options to choose from. In my last post, I showed the top 10 pizza oven designs that we had to choose from.

So, despite this lack of decision making ability that we seem to have acquired, we have finally made our decision on the style of our pizza oven. We will be building a flat roof enclosure housed with brick on the outside. Also, there will be a countertop along the front of the oven made from concrete.

The enclosure will serve two purposes.  First, it will hold in all of the insulation that will be placed around the oven dome.  Second, it will keep rain and snow from the dome.

Choosing the Enclosure Materials

When building the enclosure, there is one important thing to remember.  We are dealing with fire and an oven that will reach 1000 degrees.  Therefore, anything that can burn (wood studs, etc.) should probably be avoided in order to keep this thing safe.  To build an enclosure around the dome, a common material is to use metal studs which are then covered in a board such as durock or hardibacker.  Therefore, that is what I have done.

1. Metal Studs (8 ft):  15 @ $3.11 = $47
2. Box of self drilling screws: $7
3. Box of tapcon screws: $5
4. Hardibacker (3×5): 6 @ $11.27 = $68

Total for the enclosure: $127

Total for materials so far: $932

Building the Enclosure

The enclosure will consist of metal stud walls.  These walls are very similar to walls built in a standard framing project.  Each of the walls have a base plate, a top plate, and studs spaced 16″ on center.

Each of the baseplates should be fastened to the hearth using tapcon screws.  I had never used these before, but they were pretty easy to do.  Just drill a hole with a masonry bit a little bit deeper than the screw is long.  Then the screw goes right into the concrete just like a drywall screw goes into drywall.

Screwing in the base of the enclosure walls with the blue tapcon screws.

Building the walls are relatively simple, but time somewhat time consuming.  I had to cut the metal studs with my tin snips (I’m thinking that there is there a better way…).  How high should the walls be?  For me, I will be putting 6 inches of insulation over the dome.  Therefore, I made my walls to be 6″ higher than the top of the dome.

The finished metal stud walls for the pizza oven. Also, landing arch is now in pieces after I tore it down.

When I first put up the walls, they still felt a little bit wobbly.  That is completely normal though.  As soon as the hardibacker gets screwed onto all four sides, it will be rock solid.

Buttressing the Arch

In my post on finishing up the dome, I talked about how my original landing arch had failed due to my lack of buttressing the sides.  Since I am building a metal stud enclosure, I have decided to buttress the side of the arch using the metal walls.  Ultimately, all of the outward force of the arch will be transferred to the tapcon screws that are holding the wall in place.  It probably would have been a better solution to either build a masonry buttress or put rebar into the hearth, but this wall/tapcon solution should hold up.  I’m not planning on putting a whole lot of weight on the arch.

To provide extra support, I put another piece of metal stud angled against the vertical stud (seen in the above picture).  This should help to prevent the vertical wall stud from buckling (I don’t think it would have anyway, but better safe than sorry!)

Also, since this oven will be getting really hot, I thought to myself:  ”If this metal stud is going to directly contact the brick, it is going to get red hot and bend like a wet noodle.”  Now, in actuality, this metal stud would never get that hot.  But, just to be safe, I put some vermicrete between the brick and the metal stud to provide some insulation from the intense heat.

The metal studs are helping to buttress the base of the arch. The vermicrete between should help to keep high heat away from the metal studs.

Now that both sides of the arch are supported, I can rebuild the arch without fear of collapse.

That is the start of the enclosure.  The beginning of the end.  Next up?  The chimney!  I think I have been talking about doing this chimney for quite a while now, but these problems just kept getting in the way.  Now that the arch is properly supported at the base, I can start adding the weight of the chimney on the top without worrying about it collapsing.