Grain Depth

How important is the grain depth in the MLT? I've been batch sparging but would like to start fly sparging. I normally do 5 gal batches but I will on occasion do 10 gal batches too. With that said I'd like to be able to use the same cooler for both sizes. I currently have a stainless braid but I will switch over a cpvc manifold before the next brew day.

Thanks for the wisdom!

Nick

I have 2MLT's, one 5g and 1 10g, both Rubbermaid round coolers. I also fly sparge.
The 5g has a cross sectional area of about 254 square inches, and the 10g is 530.
I only brew 5g batches with a grain bill of about 8 - 14#, usually about 11#
I've never used the 10g MLT with less than 10# grain, and I've never used the 5g with more than 13.5#
Within those constraints, I get 85% brewhouse efficiency with the 5g, and 80% with the 10g. The percentages never seem to vary (except when I was getting used to the 10g setup). I put the efficiency difference down to the reduced grain bed depth in the 10g cooler, but there could be other factors that I am not aware of.
I find that I can sparge in the 10g cooler about twice as fast as in the 5g with no loss in efficiency (30 min for 10# vs 60 min). I put this down to the larger area, but again I could be wrong. I may also be able to reduce the sparge time with the 10g cooler, but I haven't tried it.

Hope this helps.

-a.