400 for that space is great. if you are concerned about the air/temp exchange doing done you should make a hole for the exhaust fan vent. considering it is a rental maybe you should look into a 180watt led grow it. it works just the same as hps but throws out less heat which = less head in the grow space = less opening of the doors. and you can have it closer to the plants without causing burnt leaves. if your rental includes free electricity the landlord will see how much elecriticity is being used and could have cops bother you. just giving a few insights