Effect of Lump Size On Burn Time

We suppose it was inevitable that eventually we were going to have to do this test. Recently, folks were arguing in one of the online groups devoted to kamado-style cookers that small pieces of lump charcoal burn faster than large pieces of lump charcoal. We suppose if we looked hard enough, we could find folks arguing just the opposite. This, of course, defies all logic since a pound of charcoal is a pound of charcoal, regardless of the sizes of the individual pieces. And a pound of charcoal is going to burn a certain length of time, regardless of the size of the pieces. But, sometimes you just have to prove it by doing it.

First of all, we dumped a bag of charcoal onto the ground and selected a 3-pound sample of the bigger pieces and a 3-pound sample of the smaller pieces. We then used the burn time test protocol that we use in all of our lump charcoal reviews to measure the burn time of each sample. We burn 3.0 pounds of charcoal in a small Big Green Egg at 400°F using a temperature controller. We start the clock when the cooker temperature reaches 300°F and stop the clock when the cooker drops back down to 350°F. When the temperature starts to fall, indicating that the charcoal is running out, we open the cooker one time to knock the ash off of the remaining charcoal and pile up any remaining pieces so that they will continue to burn.

Here are photos of our two samples of charcoal, one "small" and one "big." You can click on either image to display a much larger version of the photo.

3.0 pounds of "small" charcoal

3.0 pounds of "big" charcoal

So how did the two burns compare? Here are the numbers:

Sample Size Burn Time
Small Pieces648 minutes
Large Pieces651 minutes

That is less than a 1% difference between the two burn times. It should be obvious that the same weight of the same fuel is going to burn the same length of time and contain the same amount of heat. The size of the individual pieces of charcoal has nothing to do with how long the charcoal burns.

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