yea I grow on 3x4 feet (900 cm x 1,2M) or so ..
and yes .. make sure you have a nice filter to fit your ventilation (I guess you have a nice 4-6 inch ventilator for your cool tube ?)
as the stink will ! become really bad once they flower ..
sumthing like this:
for a 600W HPS .. even in scandinavia I wouldn't like to go with less then a 5" specially if it have to pull through a cool tube/tubing's
high temperatures can really become a issue ...
I did`t have a cool hood for my 600W this summer and I ended up with temps around 32-34C on hot days
even running it at night .. with out a cool hood/tube I had temps raise 5-8C compared to outside/ambi temps now with my coolhood I only experience 1-3C hotter then outside the grow room ..
so now I can keep it at them perfect 27C when I have 24-25C outside (in my appartment .. witch is kind a perfect .. cept on hot summer days .. plan ahead .. veg doing the summer month)