Going back to the original message in the thread, I just made a new mash tun out of a 9 gal. rectangular cooler, and I ran a similar experiment to the one lefty ran, where I heated 3 gal. of water to ~170, let them sit in the mash tun for 10-15 min., and then added ice and stirred until the temp. was down to ~154. After an hour, I lost about 8 degrees to end up at ~146.
My question is, does anyone have heat loss numbers for a similar experiment using a mash tun they know reliably holds temperature during an actual mash? I realize that adding grain will lead to less heat loss, but before I try a batch in this mash tun, I want to make sure my water-only heat loss is within acceptable bounds.