I use this in a large room - 70 sq metres - and it is effective. It brings the temp down slightly - by about 3 degrees - but more importantly it dehumidifies the space so the real feel is down by 10-15 degrees. It's important to have a well insulated space. You have to be able to keep external heat out and the cool air in before these will work effectively. A lot of rental properties are not insulated and unfortunately a unit like this won't work effectively in those properties. Heat transfer occurs through windows but there are simple tricks to combat this eg DIY thermal blinds and/or bubble wrap taped to the windows. A portable can never be as effective as a split system but they are cheaper and they blow cold air unlike a fan.