<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Mike Provance:
[qb]It would seem to me that you would be using up energy keeping the water hot or the sand hot. That energy could be used in having a longer burn if you were not having to keep a filled water pan heated. Am I right or wrong?[/qb] <HR></BLOCKQUOTE>You're right.
My opinion is that Weber incorporated water into the design of the cooker to help users control temperature more easily and to moderate temperature at the bottom grate. Weber was willing to trade some fuel efficiency to achieve these goals.
I know it's a crude analogy, but I think of water in the WSM as like control rods in a nuclear reactor. In a reactor, the control rods keep the nuclear reaction in check by absorbing extra neutrons. In the WSM, the water keeps the temperature in check by absorbing some of the heat energy.
Also, water absorbs 5x the energy of sand per pound, and since it evaporates when heated and can be replenished, it is a better "consumer" of heat energy than sand.
Can you control temperature using only the vents and an empty pan? Yes, as long as you're really careful to start with a small fire and keep it choked down throughout the cook. Take a look at the
Smoke-Dried Tomatoes article, where I ran the cooker at 150-160*F for 26-1/2 hours using the Minion Method with the top vent set 50% open and one bottom vent set 20% open.
Regards,
Chris