exhausting my air

Hi guys and gals. I'm a total newbie just about to start my first grow. My main problem is exhausting my grow room air. I'm going to grow in a top floor bedroom and was going to exhaust into the attic. I'm aware that means a lot of warm air and moisture. I was thinking of venting through the bedroom ceiling and into a 50 litre water butt to catch moisture. I'm hoping the air will just dissapate through the cracks up in my drafty attic. I'm running a inline 8inch fan from a 2mx2mx2m grow tent with 2 600w lights. It's all still in the boxes while my babies sit in their propagator. The reason I'm thinking of the water tank is because I'm very nervous about punching a 8inch hole throgh my chimney stack. Any advice would be very much apreciated.

Not a real clear picture. If exhausting into the attic, via the ceiling, moisture won't be a problem. Most attics are designed to deal with hot air. In a passive manor. A little more ware are won't hurt.

thanks alot. I just needed a little assurance.