Originally posted: 11/01/2003
Last updated: 04/11/2009

In September and October 2003, I conducted three temperature "experiments" to test water pan variations in the WSM.

Each session consisted of cooking 2 whole chickens. All chickens were fresh, natural fryers, not previously frozen, and weighed 3-1/2 to 3-3/4 pounds each (Picture 1). Each chicken was prepped as follows:

• Giblets were removed.
• Excess fat was trimmed from the body cavity opening.
• The carcass was cut down one side of the backbone, and the backbone was left intact.
• The keel bone (breast bone) was removed.
• The carcass was cut into two halves.
• No rub was applied.

Each session had a different water pan treatment:

• Session #1: The water pan was empty. It was covered with wide, heavy duty aluminum foil inside and out.
• Session #2: The water pan was filled with 1 gallon of hot tap water. Only the outside of the pan was covered with foil. The water was not replenished during the session.
• Session #3: The water pan was filled with 8 pounds of clean playground sand. The pan was approximately 3/4 full. The pan was covered inside and out with foil, then the sand was added and compacted (Picture 2), then two layers of foil were placed over the sand (Picture 3). The sand-filled pan was at room temperature when placed inside the cooker.

To measure temperature inside the cooker, a k-type bead probe thermocouple was attached to the center of each cooking grate (Picture 4). The bead was positioned 1-1/2" above the grate surface. The ETI 1305 data logging thermometer (Pictures 5) recorded the temperature from each probe at 5 minute intervals.

To measure temperature at the lid, I checked the Trend Model 33 industrial-grade bi-metal thermometer at 15 minute intervals, manually recording the temperature in a cooking log. This thermometer is mounted in the lid opposite from the lid vent (Picture 6).

For each session, the cooker was fired with a 10-pound bag of Kingsford charcoal briquettes using the Minion Method:

• Twenty coals were lit in a charcoal chimney and spread evenly over the remaining unlit briquettes.
• The cooker was assembled and the chicken added immediately, straight from the refrigerator.
• No smoke wood was used in order eliminate it as a variable in the testing.
• A single bottom vent was used to control temperature, starting at 100% open and adjusted as necessary to maintain 225-250°F.
• The top vent was fully open at all times.

Each cooking session began at 7:45am and lasted 4 hours. Weather conditions were similar on each day: clear skies, calm conditions, outdoor temperatures starting in the mid 50's and going no higher than 70°F by 11:45am. The WSM was shaded so that direct sunlight would not affect cooker temperature.

Graphs and data tables for each cook are shown below. Time represents the number of hours/minutes elapsed during each session. Bott Vent % represents the amount open a single bottom vent was set at the time indicated.

Here are some statistics based on just the last three hours of each session, when the cooker was maintaining the 225-250°F target temperature. Given that there are far fewer data points for lid temperature, I have not included lid measurements in these statistics.

Here's what I take away from the experience of conducting these three cooking sessions and looking at the raw data and summary tables above.

• My subjective impression was that none of these methods was difficult from a temperature control standpoint, but that using water was a little bit easier than either sand or an empty pan, both of which seemed about the same in terms of temperature control.
• The difference in temperature between the lid and top grate is quite variable regardless of water pan variation used. During the middle two hours of each session, the difference ranged from 0-15°F, then during the last hour the difference lessened and in two cases actually went negative. For the empty water pan cook, a 24°F difference was observed during the last three hours, from a high of 14.6°F to a low of -9.7°F.
• An empty water pan resulted in the lowest average difference between top and bottom grate temperatures, while water and sand were about the same at 5°F higher.
• Based on standard deviations, sand resulted in more stable top and bottom grate temperatures than either water or an empty pan. However, water resulted in a slightly more stable difference between top and bottom grate temperatures.

Obviously, these statistics and conclusions are just a snapshot based on three cooking sessions, and I caution readers to not extrapolate these results to other cooking situations, including other cooker firing methods and fuels, different varieties and quantities of meat, longer cooking sessions, and different weather conditions. Still, I hope that in some small way, they give you some insight into what is happening inside your Weber Bullet when you fire it up. And as I said at the beginning of this article, I'll do more tests along these lines and post the results here in the future.

I invite readers to let me know if I've screwed up in any way with this these statistics and conclusions. If I've drawn conclusions that are not supported by the data, or I've overlooked conclusions that are supported by the data, please let me know so I can correct this article.