ok...now we're getting somewhere.....your space is good enough....for 5 plants that is....the air will be renwed every time that you open that door....you don't have to keep it open for one hour.....you see, every time you open the door a small stream is created that exchanges the old air with new....in the meantime any odours will escape to the outside....the plants start smell from week 3 or so during vegetation, only the smell gets stronger as the plants get bigger....now i am in week 2 of flowering and i can manage to handle the smell by burning a candle right outside my growroom....propably i will have to burn more candles as the time goes by and my ladies produce their flowers...burning candles is really helpful because as they burn, they kill odours and produce CO2 by consuming the O2 that is in the air.....maybe you can handle the problem better by using an ioniser which produces negative ions that clean the air...i replied to another question you posted to this forum already.....your space of 1,5x1,5 meters is ok for your 400 hps and can accomodate maybe another 3 plants....keep it at 5 though as when they grow to 3ft/1meter you will be able to move around them....i grow 8 plants into a space of 1,5x0,8 and i am simply not able to handle them without changing their positions every time i want to tie them down or do something with them.....if you have any questions , simply ask....there are many people over here that will gladly answer them!