With temperatures rising, one thing’s for certain: your utility bill will, too. Now’s a good time, before the thermometer hits triple digits, to assess your cooling needs for the summer. At the very least you should check and clean your equipment, whether you cool your home with central air, room air conditioners, or good, old-fashioned ceiling fans.

If you’re replacing an old room or central air conditioner, the choices on the market today are likely to be more energy efficient than what you have. But don’t buy too little or too much—getting a cooling system that is the wrong size is the most common mistake people make, regardless of the type. Underestimate your cooling needs and you could be hot and sticky and still increase your electric bills. Buy more capacity than you need and you may wind up with a cool, damp space.