I think it would be risky putting any size.  If the module is not evenly heated it will create condensation.

I seen a guy at a lan-party once that did use 2 large peltiers to create a mini air conditioning unit for his case though.  Not sure how much cooler it got in the case but it had a 5 inch fan blowing across copper fins that had been cooled to frost just about.  They are cheap enough to buy on ebay.  Could be a fun little project if your bored.