While many homes have central air-conditioning, that is not the case everywhere. If you don’t have that convenience, and you aren’t willing to invest in having a system installed, your next best option will probably be a window-mounted air-conditioner. These units can be quite powerful, all the way up to 23 thousand BTU, which is enough for cooling several rooms in your home. Having a large air-conditioning unit mounted in your window does bring some risk with it. It is possible for them to fall out if they aren’t installed properly, and that could potentially hurt or kill someone that happens to be below, but even if that doesn’t happen, it is definitely going to force you to buy a new unit.
A good safety precaution is to install a bracket underneath your unit for support, but many of the larger units actually come with some support that can be installed.
There are some newer models available that are designed differently to allow the window to close almost completely after the unit has been installed, but you will still be dealing with cracks that insects can make it in through, so you might need to seal up the area around your air-conditioner.