you could buy a breaker box that only holds the number of breakers you need. there's no building code that i've ever heard of that requires empty breaker spaces in a box. however, if, in the future, you needed an additional breaker for a new appliance, etc., you'd be out of luck. i'm not an expert-my mother and brother are electricians-but those couple of extra spaces can come in handy. when we built our house in 2000, we got a slightly larger box with extra spaces, in case we needed them later on.