How to Choose the Best Air Purifier For a Windowless Room


Some homes, especially townhomes, oftentimes have interior rooms without a window. It’s hard to ventilate those rooms for obvious reasons, so an air purifier is one of the few solutions to keep its air fresh.

But how do you choose the air purifier that’s best for a room with no windows? Choose an air purifier that will overcome the poor natural ventilation in the room. To do that, an air purifier that can change the air in the room at least 4 times per hour is best. You’ll also have to match the CADR rating of the air purifier to the volume in the room, as well as look for air purifiers with filters that can remove the majority of pollutants.


Air Flow Matters

In a room that’s closed off to fresh outdoor air, it’s important to mix in as much of the air coming through the shared ventilation system. Here, a powerful air flow matters more than in a regular room with a window since it’s so far away from any access to fresh air.

Air purifiers are measured based on something called the air changes per hour, or ACH.

As its name implies, the ACH simply tells you how many times the same air can cycle through an air purifier in an hour. For example, if the ACH is 3x, it means that the air in the room is fully changed out 3 times per hour, or once every 20 minutes.

This comes with a caveat, however, which brings me to another acronym – CADR.



In my opinion, air purifiers aren’t as well regulated as they should be. Many imported products don’t give a consumer the full information needed to make an informed decision.

And if you’re trying to air out a room with no window, then you really need to pay attention and insist on a product that follows a standard called the CADR.

CADR stands for Clean Air Delivery Rate, and is displayed as an AHAM Verifide label on each air purifier (if the manufacturer voluntarily chooses to participate in this verification program).

ACH alone won’t tell you exactly how much air can move through an air purifier, it only tells you how quickly it can move. So you’ll need the CADR to give you this missing information. The CADR measures how many cubic feet of air per minute an air purifier can take in while removing 80% of pollutants.

If this sounds like a lot of units and acronyms, let me give you an example:

Suppose you have a windowless room that happens to be 12 by 12 feet, and has 10-foot ceilings. Multiplied together, this means that your room has a volume of 1,440 cubic feet. It also means that you need an air purifier with a CADR rating of 126 cubic feet per minute.

To calculate out the CADR rating you need for your own room, use the CADR conversion table in this post.


Understand the Pollutants in the Room

A room without a window is unique when it comes to the pollutants in the air. For one, there isn’t any natural UV light that may kill off mold, viruses, or bacteria. This is most likely in basement and lower level rooms. At the same time, the lack of windows will provide for a room with less humidity in many cases on higher levels of the home.

Also, if your home is a new construction home or you’ve introduced new flooring or furniture into this room, any toxic gases from those products will take longer to off-gas if its ventilation is poor.

You’ll have to understand what kinds of pollutants are affecting the air in this type of room the most, and then address them. Larger particles like dust, pet dander, and pollen will be removed by most air purifiers, even the less expensive ones. Finer particles like tobacco smoke, cooking oil smoke, bacteria, and volatile organic compounds (VOCs) can only be removed with a True HEPA and activated carbon filter combo.

There are some air purifiers that have built-in UV light. While some are safe, many can create ozone, which is dangerous. So just make sure to do your research.


Combining ACH, CADR, and the Filters You Need

Now that you know the main points you must focus on, you’ll have to combine them.

First, I recommend at minimum an air purifier with an ACH of 4x or 5x, and even more if the room gets little ventilation or is stuffy. Second, look for an air purifier with an AHAM Verifide label and don’t trust everything the manufacturer claims its product does, unless it’s independently verified. Third, match the CADR rating with the volume of your room.

And lastly, look for an air purifier that has the types of filters that will remove the pollutants that are present in the room. My advice is to go for an air purifier with both a True HEPA and a heavy, granular activated carbon filter. It’s a worthwhile investment.

Check out my recommendations for air purifiers.