This is a test of commonsense. Complete the next sentence:

How to choose an air purifier for allergies
Choose a room air purifier.
This is your only option for an air purifier if your home doesn't have forced-air heating or cooling. These range in weight from 10-20 pounds, have a handle for moving, and stand on the floor or table in the room of choice.
They generally cost less than whole-house models, ranging anywhere from $60 to a couple hundred dollars. Room air purifiers require annual replacement of the filter that captures airborne particles responsible for allergies.