I am considering getting a either a 7 gallon or a 14 gallon conical fermenter and am wondering if it would be okay to ferment a standard 5 gallon batch in the 14 gallon or if that would be a bad idea. Thoughts?
If you want consistency then I would not recommend brewing in the wrong size vessel. If you don't care, go for it.
For further reading http://www.scientificsocieties.org/JIB/papers/1992/1992_98_6_509.pdf
Actually I agree with brewchez. I did some further reading and it does appear that you can ferment a 5 gallon beer in a 14 gallon conical. Where what I said really applies is to fermenters that are 15' or higher. At this point the hydrostatic pressure at the bottom of the tank begins to inhibit yeast growth. Additionally on Blichmann's website, it says at the bottom that you can brew 5 gallons of beer in a 14 gallon conical.
I am now interested to trying to brew a 5 gallon batch in my 15 gallon cylindrical-conical and comparing it to a beer fermented in a glass carboy.
The answers above are right, but I'd like to point that using a conical so big leaves much space obtained by air. I think it would be better if you used a smaller one so that less air rests inside and there is a smaller probability of the beer getting oxidized.