So if you're using a converted 10 gal cooler, this is what I'd do.
You have 8.25 lbs grain (don't forget to get it milled!) that is roughly around room temperature, 70 degrees. (
EDIT: BP's posted recipe only calls for 6.75 lbs of grain after reading thoroughly...where'd you get 8.5 from? Either way, with the calc I provide, it'll be a cinch changing it up, you can do that for practice!
BP says to mash at 154 degrees F at a ratio of 1.10 qts of water per pound of grain. Therefore, 8.25 lbs * 1.1 qts = 9.075 qts or roughly 2.27 gallons (4 quarts in a gallon).
I use
this calculator for my strike temps. If your grain is 70 degrees F, you're mashing at 154 degrees F at 1.10 qts per pound, your strike temp will be 172 degrees. The grist is going to act as a buffer and lower the temp of the water immediately when added. This is why you SHOULD NOT strike AT strike temp, i.e. add 154 degree water to mash at 154.
Pre-heating your mash-tun is important, you can do 1 of 2 things:
1) Boil a couple of gallons of water, dump in your MLT, swirl around, wait 15 minutes, and throw it out.
2) Bring your 2.27 gallons of water up to around 180, dump it in your MLT , and allow the temp to drop to 172, then add the grist. This is what I do with good results.
Mash for an hour, stirring once at 30 minutes.
You then want to perform a mash-out at 168 degrees
Using the Rest Calculator from the link above, you will add 3.4 quarts of BOILING water to the mash. Stir, and rest for 10 minutes.
Now, you want to lauter. This is getting the sweet wort out of the tun. Open your valve and drain the first 3/4 gallon or into a pitcher or something. You want to add this back to the MLT because it won't have passed through the grain filter bed as well as the rest of the wort. This is called the vorlauf. After this, drain the rest of the wort into your boil kettle.
The Sparge:
Sparge amount is usually 1.5 times the Mash amount. So 9.075 * 1.5 = ~13.6 quarts or 3.4 gallons. You can either sparge once or twice, there are varying opinions. If you sparge twice, simply divide 3.4 by 2 = 1.7. Heat your 3.4 gallons of water to 170 and add to the mash. Drain into the brew kettle that contains the mash drainage.
When you've collected everything, it's time to take a hydro reading for your notes.
Boil, hop, chill, aerate (more than for an extract batch!!!!!!), and pitch yeast as normal.
HTH