Can I use a 6 gallon primary for 3 gallons of beer?

[TapeDeck]

I have a 6 gallon and a 3 gallon carboy.

I want to brew an IPA, and want to secondary it, because I want to go by the book for the first batch.

I just did an Irish Stout, which I will bottle tonight, and did it all on just the primary, based on the trends I've read from threads here and elsewhere. But for the next one, the beer should get off the trub and I should be trying to clarify it for an extended period, according to the recipe.

So I'm wondering...

I know all that headspace is a bad thing for a secondary, but I'm assuming that the co2 produced in primary will push the oxygen out, largely. Am I correct, or am I assuming undue risk? I mean, I can go buy another carboy, but I feel like that's perhaps unnecessary at this point, if I can get away with one.

Thoughts?

 

[maffewl]

Headspace is no problem in the primary. The yeast want the oxygen to begin with and then it is filled with co2 when they become active. Brew away!

 

[beerman0001]

You will be fine.

 

[TapeDeck]

SWEET.

I like beer.