I'm brewing 5 gallons of AG belgian dubbel - it's boiling now. I have to chill about 7 gallons of wort to around 64F. I have a 25' 3/8" immersion chiller and a CFC. I prefer the IC cuz it's easier but am wondering if my 59 degree tap water will chill the wort to 64 in a reasonable (< 30 min) time. That led me to wonder if there's a simple calculation or calculator to do this. Seems like it would be straight forward if you knew the constants. X surface area of IC, volume of water assuming stirring, contact time, temperature differential etc.