[Don Piano]

Well first I ask; Is there is a window in there? If so, put up a shade in the window (so it looks like normal to the outside world, hang a piece of black landscapers fabric (or the like) behind that. Next build a 5/6 shallow box that fits over of the window (example 3 inches deep, 2 feet wide, 3 feet tall, with only one large side, the other side will be open up against the window. Open your window a bit and attach the box, Now your window is boxed in, and you only need to put a vent collar to connect your ducting to on the face. Use 10 inch or bigger (12 would be best) and use a fan rated at close to 1000cfm for a room that size. Intake could come from the basement.

I would do a CGE (Closed Growing Environment).
Co2, Air Conditioner in the window, a fan that recycles the air through a carbon filter, and a dehumidifier. No smell to worry about, no holes to cut, and perfect temp control (as long as you use at least a 10,000btu AC unit)

When doing a "bedroom" size grow, nothing will be cheap if you want great results.

This CGE method will cost around $800-$1000 for the equipment I speak of; a 10,000btu Window AC unit, a 50 pint dehumidifier, A large carbon filter (the carbon filter should be around 3 feet long), A 750cfm inline fan to match the carbon filter, and a Co2 regulator with solenoid and timer. It will be costly but the results could make you look back and say "fuck, I'm glad I spent that money."

A 4 inch hole will not cut it at all for that size room.

I am doing stealth now, but bedrooms were my thing a few years back, and I again will emphasize, Doing a bedroom grow will not be cheap if you want killer results (which I imagine you want being that hardly anyone does a grow that big for themselves alone, this business is no different than that of any other kind, You need to spend money to make money!)