If you’re buying a whole-house air purifier, you typically don’t have to worry about where to put the air purifier. It will connect to your HVAC system that is already in your home. It will clean the air as you heat or cool your home down.
However, there are some models that do sit inside your home. You might choose this because it is less expensive than getting a purifier that connects to your HVAC system.
If this is the case, it is recommended that you put the unit in the room that you are in the most, perhaps the living room or even your bedroom.