Thermal Mass & Heat Retention

All Forno Piombo ovens (built after mid-2018) come equipped with 2 thermocouples (heat probes) installed inside the brick dome. Probe A is located inside the oven itself, which its essentially reading the cooking temperature inside the oven. Probe B is located on the outside of the 4.5” brick dome, which will tell you the thermal mass reading on the oven, or how saturated with heat the dome is.

To better understand these temperature probes and the purpose they serve, we can compare them to information displayed from a vehicle. Probe A is reading the ovens cooking temperature, which would be similar to the speedometer on a car; it tells you how fast you are currently going, or in our case, how hot our oven currently is and what temperature our food will be cooking at. Probe B is reading how saturated with heat the brick dome is, which can be compared to the fuel gauge on a car. If your fuel tank is full, you know that you can drive your vehicle at a high rate of speed for a long time. By knowing the saturation level, you can figure out how long that heat will remain in the oven once you stop adding fuel. Knowing this temperature will help you with lower temperature cooking when you use your oven to cook food in the 200-650 degree range. It is very difficult and sometimes impossible to cook at these lower temperatures using logs and fire as your fuel source, because wood burns at such a hot temperature. Normally we use wood for cooking food at 650 degrees Fahrenheit and above. For 650 and below, we use the stored heat inside the brick dome from a previous fire. This is where the value of Probe B comes in. Below is an example of where these probes are located and what temperatures they are reading.

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When paired with the right hardware, these thermocouples (probes) can gives us some great insight into the data behind our wood fired ovens. There are a wide variety of devices you can plug your thermocouples into. Some are simple digital display readers that will show you how hot the 2 probes are. Here is an example of one of these types of readers: Display Reader. Others can connect to the internet and upload and monitor your temperatures 24/7. It can be configured to send you text message alerts when certain temperatures are met, plot temperature history on graphs and much more. The DicksoneOne Touchscreen device is one of these more advanced pieces of hardware that can do a lot more than simply read your oven temperatures. Let’s take a look at the graph below which was generated through our DicksonOne device during one of our fires. The red line is showing us the oven temperature (Probe A) and the yellow line is the temperature on the outside of the 4.5” thick brick (Probe B).

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As you can see the fire was started around 2:45 PM and shot up to 750° F within 30 minutes. At this point it was maintained between 700°-950° F until 7 PM, so the oven was actively being fueled by logs for about 4 hours. Some interesting things to note here:

  • Probe B reached 500° at 10:30 PM, 7.5 hours after the start of the fire and 3.5 hours after we stopped adding logs. 500-600° is the standard high temperature that the outside of the brick dome seems to reach. When Probe B reaches this temperature we consider the oven “Fully Saturated”, meaning your brick dome has stored enough heat to slow cook at lower temperatures.

  • The temperature inside the oven dropped from 600-400° in 15 hours, giving the oven an average temperature loss of roughly 13° F per hour during this time. This temperature range could be used to cook meat and vegetables in cast iron or our custom grill accessory.

  • The temperature inside the oven dropped from 400-200° in 24 hours, giving the oven an average temperature loss of roughly 8° F per hour during this time. This temperature range is ideal for slow roasting and bread baking.

Knowing how thermal mass works in your oven is crucial to cooking at lower temperatures, and that is where our temperature probes come in handy. Cooking over a period of a few days using retained heat is a fun and efficient way to use your oven. Below is an infographic on how you can utilize the heat from one fire to cook your way through the weekend.

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This is just a small example of how you might utilize your ovens heat retention to cook all weekend. Again, there is a learning curve when it comes to low temperature cooking in your wood fired oven, but it is a challenge that most of our customers seem to embrace. Our temperature probes are simply a tool meant to help you understand how thermal mass works in your oven, one of the first steps to mastering your wood fired cooking endeavors. Our next post on this subject will focus more on where heat is located inside the oven. For example; cooking your food on the floor of the oven will produce much different results than cooking your food 10 inches above the floor. Look for that blog post along with many others in the near future. Please feel free to comment any questions or thoughts you may have below!

-Tony P