You can forget smell if you use a carbon filter. I've seen the ideas on making them but personally I'd recommend you buy one until you're more comfortable with the whole deal. That way you'll get a good result first time and know how everything should work. Activated carbon is really messy shit. The room I'm running mine in used to smell of cat piss / shit because we had a litter tray in there. When I kicked the kitties out and put the fan in, the room smelt 100% clean within hours. Even with 5 super strains under a 1kw lamp, it smells the same, entirely clean. It's all about air flow. Imagine the air your fan is sucking through the filter like clouds of colored smoke coming off the plants. You want all of it going through the filter. Almost all indoor grows are in an enclosed space of some sort, a room, closet or tent. One issue that you've already mentioned is heat. If you live somewhere hot, you'll probably need to get some cool air through the growspace (and fresh air always helps provide good CO2 levels). Try to seal up all of your growspace except for a duct that you'll use as a fresh air intake. Run it to something like a window or outside vent. Provided the fan is running 24/7, air will never flow back out. Because it gets harder for the fan to suck air down long lengths of duct, the pressure in your growspace will always be slightly negative, so any holes you've left will have air being sucked through them, not leaking out. The same tricks are used in laboratory design, but in reverse. If you're working with some sensitive samples and need really clean air, they blow air into the room quicker than it can get out. That way, whenever a door or something is opened, the clean air blows out blocking any dirty air from getting in. -like my reply? pls vote in my bulb poll (sig)-