For general advice on brick oven management, I recommend visiting Forno Bravo. Go ahead, I’ll be waiting…
Managing such a small oven introduces a few complications to the fairly straightforward instructions given at Forno Bravo. Fire needs three things: fuel, oxygen, and heat. The problem here is that the sort of fire you see in all the pictures just plain won’t fit in this oven, even though the wood itself might fit. If you stuff the oven full of wood, it will smoke, sputter, and go out. The fire needs more oxygen, but you may be reluctant to make a small enough fire, thinking that it won’t get hot enough or have enough fuel. You’ll be pleasantly surprised that you’re wrong.
Building a hot clean fire is a skill that you may not have needed before now, even if you were/are a boy scout or pyromaniac. I recommend visiting woodheat.org to learn all about building a clean-burning hot fire.
Fire needs oxygen. When wood get really hot, it gives off smoke and gasses. When your fire is hot enough, and if there is oxygen, the smoke burns. When your fire is not hot enough or there’s no oxygen, the abundance of smoke exacerbates the problem by driving out the oxygen. The solution is to develop a good draft. The ideal airflow is oxygen coming in at the bottom of the door, flowing back to the fire, and hot air rising to the top of the oven and going out at the top of the door. Maintaining this draft is easy when there’s lots of room above the fire for the smoke to get out of the way of the oxygen. When there’s less room above, we need to ensure that the smoke has somewhere to go. My rule of thumb here is to not stack the wood higher than half the height of the door. As you get further back in the oven, you can go higher, but if you’re anywhere forward of halfway back keep the fuel, and fire, low.
Many instructions say to build the fire “just inside the door” and let it burn to the back of the oven. This works in a small oven just as well, but “just inside the door” means about ⅓–½ of the way back. If you build the fire right at the front, it will not establish the draft and will just go out. Plus you’ll lose all your heat.
Keeping the fire low and bright means, more than anything, that you need small firewood pieces. The Italians use bundles of sticks or branches called faggots. Big logs are just going to take up a lot of space. Plus, you don’t need that much wood. You’ll be surprised just how little wood you need to saturate this small oven. I recommend splitting your logs to about 2ʺ–3ʺ, and some smaller kindling.
Fire is like Conway’s Game of Life. Each piece of wood needs a couple friends, but not so many friends as to restrict oxygen availability. Build your front-back fire in such a manner that as the fire burns back, and gravity drops the coals to the floor, there will always be plenty of coals and fuel and no lone sticks. This will take a little practice, but it’s a lot of fun.
Fire burns best in cycles. You don’t want to be constantly feeding fuel to your fire, because each time you put a cold stick on the fire it takes a lot of energy, restricts oxygen flow, and belches smoke. Try to build your front-back fire so that you only need to ignite the newspaper and watch it burn down to embers in approximately one hour. In practice, you may need to add fuel when things get too thin—in that case add something small enough to catch fire immediately without smoking.
In conclusion, remember the cardinal rules: use sticks not logs, give the fire room to breathe, burn in a cycle, and keep the fire bright and smoke free.