Unless you have AC with CO2 ammendment, you CANNOT grow without fresh air. Plants grow by using photosynthesis. Photosynthesis needs several elements for it to work, light, nutrition, water and CO2. Plants grow better at certain temps & humidities also but can grow in far from perfect conditions but not without the basics. It is like you trying to survive without Oxygen (did you see the film Apollo 13?) As the plant uses CO2 from the air, it replaces it with Oxygen, great for you, bad for the plant. Thats the bad news, heres the good news. Get a carbon filter & extractor fan, seal your room with one in vent & 1 out vent. Ensure you have less air being sucked in than blowing out, this creates negative pressure which will stop smells escaping unless they go via your exhaust which is via the carbon filter! You should be looking to exchange the air between 1 & 4x per min. A carbon filter reduces performance of fans by around 25% and bends in ducting reduce it by around 15%. This is the calculation you need to give you a well ventilated room. LxWxH= Room volume. between 1 & 4 times per min is recommended, I prefer 2x per min minimum. Room volume x 2=Air exchange. Air exchange + 33%(to allow for a 25 reduction, 33% has to be added) = Carbon filtered air exchange. Carbon filtered air exchange x17.5% (to allow for a 15 reduction, 17.5% has to be added) for each bend in ducting = Fan rating needed. eg, a 3ft sq x 6ft high tent with a carbon filter and one bend in the ducting would give the following calculation. 3 x 3 x 6 = 54cubic ft. 54 cf x 2 exchanges = 108 cf/m + 25% = 144cfm + 17.5% for bend = 170cfm. This is the minimum fan size for the spec room detailed. Hope this makes sense, if not pm me with your room size etc & I will work it out for you. Peace W