How Well Does A BGE Table Nest
Protect A Wooden Table?


Introduction
We recently published an article titled "What Material Should You Use Beneath Your Kamado-Style Cooker On A Wood Table?" in which we compared concrete paving blocks to various other materials for use in protecting your wood table from heat radiating from a ceramic cooker. If you wonder why you need to protect your table, you need look no further than these photos:

Damage to a wooden table when using a
2-inch thick octagonal concrete paver.

A wooden table that got charred despite
using a concrete paver.

Damage to a wooden table when using a
BGE ceramic feet.

Another wooden table almost set on fire.

So, what's the answer? Well, various insulating materials do provide varying degrees of protection. But what about the Big Green Egg Table Nest? The table nest is the Big Green Egg answer to "what should I place under my cooker on a wood table," but how well does it protect the table versus some of the insulating materials we tested. That's what we set out to find.


What Is A Big Green Egg Table Nest?
The table nest is made up from two steel bars bolted together at right angles. The ends of the bars are shaped into "legs" that hold the cooker, in the case of the table nest for a large Big Green Egg cooker, about 1⅞ inches above the surface that you place it on. The cooker then simply rests on top of the steel bars. This provides a region of air beneath the cooker:

Table nest for a large Big Green Egg ceramic cooker.


Thermal Conductivity
Thermal conductivity measures the ability of a material to transmit heat via conduction. In the International System of Units (SI), thermal conductivity is measured in watts per meter-kelvin (W/(m·K)). We won't bore you with the details, but suffice it to say that the bigger the number when looking at thermal conductivity, the faster heat is conducted through the material. Conversely, the smaller the number, the better the material insulates.

What distinguishes the table nest from all the materials we tested in our previous article is that the table nest uses air to protect the wood table and air has a very low thermal conductivity. Here is a list of the materials tested previously to which we have added air:

Material  Thermal Conductivity  
  Refractory (Heavy) Fire Brick  
1.40 ²
  Concrete (Paver)
1.13 ¹
  Kiln (Insulating) Fire Brick
0.24 ³
  Vermiculite Brick
0.18
  Calcium Silicate
0.07
  Air (room temperature)
0.026

Table 1. Thermal conductivity of various materials used in this project.


As you can see, air does not conduct heat very well, so air should be a good insulator between your cooker and your table. But that's not the whole story. You also need to consider radiated heat. What's that? Heat transfer from a body with a high temperature to a body with a lower temperature, when bodies are not in direct physical contact with each other, is called heat radiation. Air is not very good at stopping radiated heat while all the materials we tested previously completely block radiated heat. As a result we can't just look at the table of thermal conductivities and conclude that the table nest is the best choice. We need to run a test and see what happens.


How And What We Tested
We decided to compare the table nest with vermiculite splits. The vermiculite splits are relatively easy to obtain and were the second best material we tested. In addition, vermiculite can be sawn with a wood saw. With 9 vermiculite splits and one saw cut, you can assemble a 13.5" x 13.5" base for a large Big Green Egg.

So, what are vermiculite splits anyway? Vermiculite is a naturally occurring mineral formed into a pressed piece of board and then cut into shapes. Vermiculite fire bricks are non-combustible, a fire resistant product which is light and easy to cut with a wood saw, unlike heavy clay fire bricks. Vermiculite fire bricks have excellent thermal insulation properties and have minimal shrinkage at high temperatures.

Top view of our vermiculite base.

Side view of our vermiculite base.


Since we don't have a ceramic cooker that we can easily place on top of the two test setups, we just tried to simulate something close to that. We aren't interested in the actual temperatures, but rather we are comparing the two setups. So for this testing, we decided to simulate a more realistic setup by having a wooden base (as opposed to a concrete paver), the insulating material on the base, and a pizza stone on top of the insulating material. We then placed a chimney starter on the pizza stone to complete the setup. Here is a diagram to illustrate:

Setups for the table nest and vermiculite tests. The location of the thermocouple is indicated by the red dot.


And here are two photos showing the actual setup in action:

Table nest setup.

Vermiculite setup.


Results
We know the vermiculite did an excellent job in our previous test, so now we can determine if the table nest does a better job or not. So, how did the two setups do?

Vermiculite: Let's start with the setup that used vermiculite splits to insulate the wood table from the fire in the chimney. It was pretty straightforward and requires no real explanation. After about 3 hours and 30 minutes, the vermiculite split setup peaked at 320°F.

Table Nest: The results of using the table nest are a little more complicated. We are using a layer of air between the wood and the pizza stone. That air is subject to breezes and obstructions. As a result, we really have three results:

  1. No obstruction: This configuration is as you see it in the photo above. It simulates having a cooker on a table nest in an open table where air flow is not obstructed from any direction. During this phase of testing, we observed an average temperature of 165°F and peaks up to 209°F
  2. Significant obstruction: We don't have a photo to show you, but in this part of the test, we placed ceramic half-round deflector plates on four sides to block most of the airflow underneath the table nest. During this phase, we observed a peak of 400°F. We chose to stop at that point for fear of damaging the wood surface and possibly our thermocouple.
  3. Moderate obstruction: Again don't have a photo to show you, but this part of the test was to simulate a cooker in a table which has the cooker enclosed on three sides. We removed one of the deflector plates. We also moved the other three further away so that air could circulate, but a light breeze wouldn't affect the results. In this setup, we observed an average temperature of 229°F and a maximum temperature of 253°F.
Here are the results in tabular form:

Setup  Temperature  
  Vermiculite Splits  
  Maximum 320°F  
  Table Nest Unobstructed  
  Average 165°F, Maximum 209°F  
  Table Nest Moderate Obstruction  
  Average 229°F, Maximum 253°F  
  Table Nest Obstructed  
  Maximum 400+°F  


Conclusion
Vermiculite splits performed admirably in our previous test in which we compared thermal conductivities of various materials. However, compared to the Big Green Egg Table Nest in a test that more closely approximates real life setups, we find that unless you significantly obstruct the airflow beneath your cooker, the table nest is the better choice. Only if you block the airflow beneath your cooker sitting on a table nest does the table nest fail to protect the table. As long as air can circulate beneath your cooker, the table nest does indeed provide the best protection.

Big Green Egg table nests are available in a variety of sizes. We found them for the medium, large, extra large and 2XL cookers. If you don't have a Big Green Egg cooker, you should still be able to use one of their table nests to support your cooker and protect your wood table.


What About Other Materials?
We'll repeat this information from our previous article should you be curious about materials such as slate pavers and ceramic tiles. How do these types of materials work for insulating a wood table? The following photos should provide the answer:

Ceramic tile that has shattered from the heat of the cooker.

Another ceramic tile that has shattered from the heat of the cooker.

A sheet of slate that has shattered from the heat of the cooker.


As you can see, these materials are totally unsuited for exposure to heat. We know from personal experience that slate is a poor choice. We had 3 sheets of slate crack just like is shown in the last photo. It is best to stick to materials made for exposure to heat or a table nest.


Sources For Materials
We'll also repeat this information from our previous article in case you are interested in obtaining the various materials that we tested. Regular fire bricks can usually be found at your local brickyard, Home Depot, Lowe's etc. Here is where we obtained some of the materials we tested:

Big Green Egg Table Nest – Any Big Green Egg dealer should have table nests or can order them.
Vermiculite splits – 9 for $44.00 from Neuex Hearth Products
Kiln (Insulating) fire brick splits – 6 for $39.95 from Amazon, Lynn Manufacturing
Kiln (Insulating) fire bricks – 4 for $32.90 from Amazon, All About Steel
Refractory (Heavy) fire brick splits – 6 for $36.99 from Ace Hardware, Rutland Products
Cement Pavers – $1.78 Lowes
Calcium Silicate Insulation – 12x12x1, $25.23 from Grainger. Also available from
     from Neuex Hearth Products who can provide custom sizes.


Citations

1. Field and Laboratory Assessment of Different Concrete Paving Materials Thermal Behavior,     Ivana Bariši´c, Ivanka Netinger Grubeša, Hrvoje Krsti´c and Dalibor Kubica, Sustainability 2022.

2. Heat Retention Qualities Of Fire Brick, Steven Colbath, HomeSteady web site

3. Ibid, note 2.

4. Thermax Boards SF (1100°C) Technical Specification, SF750 vermiculite technical data.

5. Thermal conductivity of calcium silicate insulation..., The Engineering ToolBox web site.

6. "List of Thermal Conductivities", Wikipedia.


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