Consumer Reports tests the "comfort" level of portable air conditioners based on how a model cooled a room sized for the particular unit (on its low fan setting) and how accurate it came to meeting the temperature set point.
If central air conditioning isn’t an option, room air conditioners can be an inexpensive and energy-efficient alternative for cooling one or two rooms.
The average household spends 13 percent of its annual utility bill on cooling, according to Energy Star. So it’s important to choose the right unit. An air conditioner that's too small will struggle to cool a room. One that's too big cools so quickly that it doesn't have time to remove enough moisture, leaving you with a cold, clammy space.