28" Oven in Seattle

[JBA]

Just as many others, I've dreamt of having a wood-fired oven in my backyard, and how to achieve that dream. After considering many existing options out there, the layout of my backyard is really only able to support having a small-ish one built in place. This thread will capture the journey of building one.

This is the dedicated site:


Two 3D sketches with accurate measurements of the oven in the backyard (yes I have a full 3D model of my yard)

[JBA]

Even though the oven will be on the smaller side, my goal is for it to be able to retain a lot of residual heat to allow for baking and roasting the day after cooking pizzas.

More renders of the oven design (this is not a rough design, all components are true to size):





(pictured CalSil board is only 2" in this picture, but has been expanded to 3" in latest model)



Notable features in the design to allow for lots of heat to be retained:

- 3" CalSil Board as insulation for the oven floor.
- 3" insulating blanket for the dome + 2 inches of 10:1 vermicrete before final render layer
- Dome built on top of floor, not outside for ease of construction
- Floor bricks laid on the side to increase thickness to 4"

[JBA]

As I begin amassing materials and tools to build the oven, are there any tips or suggestions on where I could save time or money?
Currently, I'm looking at a total build cost of $3500 to $4000 if I'm sourcing materials from Lowe's/Home Depot. Some of the big ticket items are:

$750 for about 170 fire bricks (3.78 each)
Almost $500 for waterproof CalSil board of 3" thickness
Dome insulation is likely to be a few hundred dollars
Vermicrete and concrete is going to be another few hundred dollars
Refractory cement from Home Depot is about $60 per 25 lb bucket. I expect to need 3 or 4 of them

When it comes to an oven door, are there any good and well-insulating designs that don't require welding?

As for tools, can I get away with just an angle grinder and a circular saw with diamond blades for cutting bricks? I'd rather not spend nearly $200 on a miter saw

And another "hidden" cost I suspect will be things like the pizza peel, tuscan grill, cast iron pans, gloves, and other cooking tools. Probably another $200-$300 at least.

[Kvanbael]

I sympathize a lot with your amount of upfront planning. how close does the chimney run to the (wooden?) floating deck. That might be an issue for fire safety regulations.

[NCMan]

One thing I would say, IMO, once you use 3" of blanket, it's really a waste of time, money and precious space to then apply any vermicrete. Plus, that small amount of it, really doesn't do much for actual insulation. I'd skip it and make your oven bigger. Also, if you do decide to use it, I'd go with 8:1. Just my 2¢.

[JRPizza]

Lots of builders don't use refractory cement and go the home brew route, which is what I did - you can save a little money there. I also bought my insulation from Harbison-Walker in Kent. I don't know if you have checked them out yet but it's good to shop around. I live up in Lynnwood but saved quite a bit by picking up my board and blanket in the same trip. Shipping on that stuff can be a large portion of the cost. I think they sell bricks now too, but at the time I got mine at Mutual Materials. One cost I don't see on your list is chimney pipe. Double wall stainless, which you are probably going to want if you are near any wooden structures, can be quite expensive. I shopped around and was lucky to find free shipping - anything you can buy locally or get shipped free is going to be the way to go.

Also as Kvanbael noted above, you might need to extend your chimney pipe above your deck railing. I didn't need a permit to build in Snohomish County, but I needed to meet code as if I was permitted. Code has requirements for both horizontal clearance (you can be close to wood if you use double wall pipe) and vertical clearance (you have to be above any close structures by a foot or so). The sides of insulated pipe stay pretty cool but the hot end can be pretty hot!

[mongota]

You can use the homebrew mortar, it'll cost you a bag of portland, a bag of lime, some sand, and a bag of fire clay. Maybe $50-$55 total. The savings might not be terribly significant over commercial refractory until you realize you need another bucket of premade from the big box store. Could save you $50-$100? Those initial purchases of homebrew ingredients will be more than enough to build your oven. Putting those leftovers to use will be discussed further below.

Firebrick, if you're getting them locally get (for example) 150 now and as you near completion you can buy only what you need so you don't overbuy. Again, not a savings, just not wasting money. Obviously the floor brick being on edge is adding cost, but if you want heat loading the bricks on edge will afford that. I'd also recommend if you haven't already to call a couple of masonry yards in your area and ask for a cost on "medium duty firebrick, 9" x 4.5" x 2.25", I'll be needing 170-200 of them". You might find significant savings on the cost of each brick.

Yes, you can build with just an angle grinder and a diamond blade. A thin kerf blade will generate a bit less brick dust when dry cutting than a thicker blade. To minimize brick dust generation you can just taper the 'inside the oven' face edges of the dome bricks so they present a nice tapered look with typical mortar lines on the interior of the dome. You will have larger "V" gaps as you go towards the outside of the dome. Those can be filled with homebrew. By not tapering the entire length of the sides of the brick your bricks will be 'wider' so to speak, so you'll use fewer half-bricks per course. That may save you a few more bricks and would be another efficiency of using homebrew mortar over a commercial refractory mortar.

Insulation. 3" over the dome and under the floor is good, 4" would be better for your goals. Have you figured the amount of blanket required per layer vs how much comes in a box? Example, 1" blanket comes 50sqft to a box. It might be tough to get three 1" layers out of one box. A second box will give you 100sqft of insulation, enough for three 1" layers with leftover. Is the leftover enough for a 4th 1" layer? You're not buying more to go from 3" to 4". You're simply using what you're getting. Four inches of CF blanket would allow you to eliminate the vermicrete.

Price out 4" of board (two 2" layers) under the floor offset by the savings of your floor brick being flat instead of on edge. Offset the cost of 4" of blanket over the dome with not using 2" of vermicrete and being able to possibly make your oven 30" instead of 28". Yes, a 30" oven will take a few more brick. But not using vermicrete will reduce build materials and save a step of labor. This is a back-and-forth analysis. If you're truly happy with a 28" oven, then stick with it. Good to think these things through now, because once built, it's built! If you stay with 3" of insulation and a 28" oven, no worries. I'm just tossing out thoughts.

Quite a few insulated doors have been made by bending tabs over and securing the parts together with metal screws. A few have used rivets. You'll have an angle grinder. You can buy metal cutoff disks at the box store to use on your angle grinder, as well as a couple pieces of sheet metal. You'll have what you need to make your own door. If you're new to metalwork, buy bandaids too. lol

Slightly off point, I have a 42" oven with 4" of board under and 4" of blanket over. Floor bricks are on the flat. I can easily cook 3 days, sometimes 4 days with an insulated door. Day 4 cook might be a protein like a brisket or ribs at 250 degrees or so, low and slow.

Good luck with the evolving design-build. Getting started can be the hardest yet easiest part of building an oven.

[fox]

I build my ovens with 4” of ceramic blanket and 4” ceramic board under the bricks.
Home brew is about 50 times easier to use than any refractory cement product I have come across and much cheaper too.
You could spend some time considering how heat loss will occur around the door, the gallery and the chimney as that will be a heat sink loss if built from brick without a thermal break.
Also bare in mind if you are useing an insulated chimney the heat exiting the top will be high and possibly dangerous to any one in that area!

[Gulf]

One thing I would say, IMO, once you use 3" of blanket, it's really a waste of time, money and precious space to then apply any vermicrete. Plus, that small amount of it, really doesn't do much for actual insulation. I'd skip it and make your oven bigger. Also, if you do decide to use it, I'd go with 8:1. Just my 2¢.

I agree, If it is used for "insulation". However, it is excellent for shaping the dome. This one averaged 1.5 to 2 inches thick. At 3 to 1, it really can't be considered as insulation, but it got us back to the shape we were shooting for.

[JBA]

Wow, thank you everyone for some great feedback, thoughts, and ideas! While I feel like I have a grip of the general steps of the build, there are many smaller but important details that I've been made aware of now. This will help me a lot in the coming months.


- The chimney will be about 20" away from the nearest wooden structure. From what I can gather, the clearance limit set by the National Fire Protection Agency is 18". I will take closer measurements later in my design to confirm.

- As for the dome insulation: I will keep the blanket at 3". The added vermicrete layer will primarily be to get the dome back in shape. I really like the two photos provided by Gulf and I will try to use a similar method to get a uniformly shaped dome. The vermicrete would then be finished with a render layer for a nicer texture, and finished with waterproof paint.

- Sounds like homebrew mortar is the way to go. If it saves me $100 then I'm fine with it being a little extra work than the pre-mix.

- Great tip regarding Harbison Walker in Kent! I will contact them about pricing for bricks and insulation. Really hope I can save a couple 100 there.

- I'll be upping the floor insulation to 4", hoping that well help the oven retain just that little extra bit of heat.

- Great advice again on how to design and build an oven door without requiring welding. I'll of course have an angle grinder, and have a nice heavy vice already to help me with the bending where needed.

- I hadn't considered heat loss mitigation around the gallery. I will reconsider my design and see if there's something I might be able to do there.


Really looking forward to building now that more and more of my conundrums seem to have good answers and approaches to them!

[JBA]

After measuring the distance from the chimney to the nearest combustible structure (wooden deck), the distance is only 14".
Since NFPA mandates a minimum distance of 18" for single-wall chimneys, it looks like I will have to opt for a double-walled chimney.

[david s]

After measuring the distance from the chimney to the nearest combustible structure (wooden deck), the distance is only 14".
Since NFPA mandates a minimum distance of 18" for single-wall chimneys, it looks like I will have to opt for a double-walled chimney.

I've done a few ovens through a roof, but now prefer an alternative solution that doesn't involve a double flue or penetrating the roof with its associated problems. There's not a great deal of price difference, but functionally I prefer the illustrated set up and don't mind the look. Check your local building code, but ours requires the pipe be at least 500mm clearance from the gutter and the flue exit 600mm higher. A couple of brackets are needed to secure the flue to the facia board.

[JRPizza]

Are you going to have some kind of cover to keep the persistent rain off the oven or are you going to try to waterproof it? I needed both a roof and sides on the South and West sides to keep the oven and hearth dry. If you are going to leave it exposed you should research all the means to keep the floor dry (weep holes and elevated insulation) and at least consider a temporary shelter to keep the insulation dry during your build. I soaked my floor early in my build and nearly a year later when I cured the oven I had to drive the remaining water out over several days of fires.

[JBA]

The oven will not be covered by a roof, at least not the way it is planned right now. Even if I added a roof, it wouldn't be possible to build something large with enough visual appeal to really protect the oven from rain when it is windy.

Since the plan is to leave the oven exposed, is it sufficient to drill weep holes into the hearth (or perhaps form them when casting?) and elevate the insulation using a layer of ceramic tiles?

I plan to also make all horizontal surfaces as water repellent as possible, such as painting the dome with several layers of waterproof paint and setting granite tiles around the outside perimeter of the dome.

The part that would be left exposed is the fire brick that forms the gallery.

During the wet season here in Seattle and the Pacific Northwest I would try to keep the oven covered with a tarp.

As for keeping the oven dry during building - I plan on keeping it covered with a tarp when I'm not working on it. Luckily, summers are reliably dry here in Seattle which also reduces the chance of accidentally leaving it uncovered in the rain when I plan to do most of the building.

Finally, when it comes to drying fires (or curing like people like to say), I'm already expecting that to be a 7+ day process regardless if the oven or floor will end up getting soaked or not.

[Pizzarotic]

Since the plan is to leave the oven exposed, is it sufficient to drill weep holes into the hearth (or perhaps form them when casting?) and elevate the insulation using a layer of ceramic tiles?

That's always a good idea and will help dissipate any moisture that does get in.

I plan to also make all horizontal surfaces as water repellent as possible, such as painting the dome with several layers of waterproof paint and setting granite tiles around the outside perimeter of the dome.

Just remember, tiling is not waterproof as the water can still enter through the grout. Make sure you use a waterproof membrane under the tiles as well as the dome.

The part that would be left exposed is the fire brick that forms the gallery.

A outer door may help as well.

During the wet season here in Seattle and the Pacific Northwest I would try to keep the oven covered with a tarp.

Sounds like a good plan.