Calculating boil volume in partial boil?

Question

I'm an all-grain brewer but I haven't done an extract batch in years (or an all-grain one in over a year) and want to do an extract IPA this week. Looking at the various software and calculators, they don't seem to account for partial boils, just final batch size. I want to boil at about 50% volume, then top off with cold water. How do people calculate this in advance? I was hoping for something other than the hash-marked measuring stick method.

Are there any calculators or software that account for partial boils and give you total water needs up front? Oh, and god forbid, include temps (flameout wort plus refrigerated distilled water = ?°F). I like my final wort right at 65°F, ready for dumping into the fermenter.

I've always found Beersmith's water calculator to be non-intuitive by the way.

Answer 1

Measuring the water in your boil is completely based on the vessel itself. The marked stick works great, sight-tubes are wonderful, etc.

You can determine your actual pre and post boil volumes as you said, by simply going with 50% volumes.

The end water in the fermenter will be the weighted average temperature of the water added. i.e. If you have 2.5 gallons of water at 100F and 2.5 gallons of water at 50F your resulting temperature after mixing will be 75F. Simply setup your equation and solve for the necessary top up temperature. You could also whip up a pretty simple excel spreadsheet to contain this formula for usage on brew day.