Depending on your area, keeping cool during the summer could be as simple as opening your window and pointing a large 18″ standing fan on yourself, which is actually pretty helpful because fans accelerate the evaporation of the body fluids on your skin, and that evaporation cools you. In some areas, such as the Southeast, it is much more difficult to remain comfortable for two main reasons:
1: The Southeast is very hot.
2: And humidity is often high.
The combination of high humidity and high temperature is truly agonizing, because high humidity makes you feel hotter and more uncomfortable overall. The reason why high humidity (when air contains a lot of water vapour) causes such discomfort is because sweat (and other skin fluid) evaporation occurs more slowly as humidity increases, and the evaporation of those skin fluids cools your skin, which in turn cools the rest of the body. Humidity also accumulates inside the house if your windows are closed.
Ventilation has many advantages, including improving indoor air quality, keeping indoor humidity accumulation under control (mentioned above), and helping to keep the room temperature down in some cases. Ventilation can lower room temperature if your room is normally poorly ventilated (closed windows, no ventilation fan, closed doors). Never open your doors nor leave them open for ventilation.
If your house is insulated at all, then it will trap heat as it enters through the window, this is why you need to open your windows during the summer to keep cool. If you have an allergy problem, then try to set up a ventilation fan with filter without leaving windows open.
If you do not already have burglar bars, I would recommend the quick release models which enable you to open your windows much more safely without anxiety and they also enable you to escape through the windows in the event of a fire. Where I live, burglar bars are very common due to an extremely high crime rate, but I don’t mind them apart from the extra dusting required because I can open my windows without anxiety.
Burglar bars are not just for people that want to open their windows for ventilation, though. They are also helpful when windows are closed because it is often too easy for burglars to break them, dig them out, or simply push them up in some cases. You can find quick release burglar bars in many hardware stores, like ACE Hardware, for example.
Photo via RLHyde