thoughts on 5 gallon igloo/false bottom for 3 gallon batches

Not enough info to answer your question. But it all boils down to how much grain and what water to grist ratio.
See the Can I Mash It calculator at this link...

http://www.rackers.org/calcs.shtml

 

I do five gallon batches with a five gallon cylindrical water cooler. No false bottom, just a bazooka tube. Works like a champ. Some limitation on how big a beer can be made without lowering overall batch size (generally anything 7.5% or higher needs either adjustment to ratios and sparge technique, or lowering of batch size). So a five gallon cooler should work like a champ for three gallon batches. If you are making beers so big that a five gallon cooler can't mash them, NASA would like to speak with you about a job in their rocket fuel division.

 

Assuming an efficiency or 75%, it's possible you could reach 1.110 OG for a 3-gallon batch with 12 lbs of grain. Is that big enough?

YMMV, but the point is, you could do a pretty big beer!

 

I wonder how many people could get 75% mash efficiency with a 1.110 wort without oversparging the bejesus out of it.

 

No arguments here. Just pointing out that a big beer is possible. There are a number of factors that would affect the actual yield. I agree that a 1.110 would be pretty optimistic in the real world. But how big does the OP want to go?

 

I have made a few 1.075 4 gallon batches and the sparge was at the top of the cooler but it worked. 5 gallon recipes for 1.055 or so are easy without cramming. I love the 5 gallon cooler I have but it wouldnt be a bad idea to get the 10 gallon if OP wants to make high gravity or obviously 6 gallon or bigger batches.

 

I use a 9 gallon Coleman Extreme cooler for 3 gallon batches (3.5 gallons into fermenter and ~3 gallons into kegs/bottles) and I've been quite happy with it. You'll be fine with a 5 gallon cooler for most beers, but the few times I've done high gravity brews, I've been quite happy to have the extra space. Low gravity beers don't really suffer with the extra headspace (I might lose an extra degree per hour), but the thing holds temperature so well that extra space isn't really an issue.

 

My batch size is 2.5G.
My mash tun with a SS braid is 5G.

I brew a 13% ABV barleywine every year.

 

Depends on what efficiency is being measured...right?

75% extract efficiency...no problem (actually a little low)
75% brewhouse...not so much. More like 60% (65% with a tail wind).

 

I was actually talking about Mash Efficiency, which is neither of those (but generally closer to brewhouse), but I agree.

 

i'd say it's perfect. What are fermenting in? 5 gallon carboys?