Running an air purifier can drastically improve the quality of air in your home, especially as we spend around 90% of our time indoors. However, not all air purifiers are created equal, and not all models will be a good fit for your space.
For an air purifier to be effective, you need a unit capable of cleaning the air multiple times per hour in the space where you will be using it. And the best way to assess how effective a specific model will be is to pay attention to its CADR in relation to the size of your room.
CADR stands for Clean Air Delivery Rate. It is a score calculated by measuring the volume of clean air produced by the air purifier when used to remove dust, pollen and smoke. In simple terms, the higher the CADR score for each pollutant, the faster the air purifier filters the air. When you combine this score with the size of your space, you can find out whether a unit is powerful enough to effectively clean the air based on how big the space is.
Unfortunately, most air purifier manufacturers will inflate the room size recommendations by looking at how large a space the air purifier can cover based on it offering just one air change per hour. That is why you will find very small devices on Amazon that are recommended for spaces as large as 1,000 sq. ft.
Ignore the room recommendations you see in marketing materials and Amazon listings.
Always run the calculations yourself.
Calculate the CADR you need in an air purifier based on the size of your space
If you buy an air purifier that is too underpowered for your space, it will struggle to deliver clean air fast enough to make a positive difference.
That is why, before you buy, you need to find out what CADR you should be looking for in a unit to make sure it will perform well in your particular room.
Step 1. Measure the size of the room
First, you need to measure your room accurately to know how much air your purifier needs to clean.
Whether you’re using a laser measure or good old-fashioned tape, you will need measurements for the length, width and height of your room:
With these three figures, you can work out your space’s square footage and volume.
Step 2. Calculate the CADR needed to effectively clean the room
To calculate the required CADR for a room, multiply the room volume you worked out on step 1 by the desired air changes per hour (typically, at least three).
Alternatively, you can simply fill in the dimensions of your room and our calculator below will automatically work out what CADR is required to clean your space.
Step 3. Do your research into the air purifier you like
Now that you know which specifications you need from an air purifier, it’s time to find out what else you should be looking for.
This is where a little research goes a long way:
- Find the CADR certificate of the air purifier you’re considering by searching the ENERGYSTAR database.
- Check the CADR of the unit matches the minimum you need based on the size of your room.
- Aim at getting a unit that will offer a higher CADR than you require so you can run it at lower fan speeds for quieter and less power-hungry operation.
- Air purifiers can come with different types of filters to remove pollutants from your air. If you want to remove dust and pollen from the air, look for a good quality particle filter (HEPA or MERV will do). If you want to tackle smoke, viruses and bacteria, look for medical grade HEPA (H13). If you want to rid the air from unwanted smells or VOCs, then look for devices that also come with an activated carbon filter.
- The fans inside air purifiers can be noisy, so be sure to check the air purifier’s noise output before buying one. Here, too, manufacturers tend to tweak figures to make them look better than they are, so check our reviews to see what the real-life sound levels are. If noise is an issue for you, check out the new generation of PC fan-powered air purifiers.
- Air purifiers can be power-hungry. Considering you should be running yours 24/7, it is important that you calculate how much they will add to your electricity bill. You can use this calculator from the U.S. Department of Energy to get an idea based on how much power the device consumes.
- Many modern-day air purifiers come packed with smart features like air quality indicators, auto mode and app connectivity. Consider if these features are worth paying extra for, based on your specific lifestyle and how you use appliances at home.
Read our guide on ten things you need to know before you buy an air purifier – or watch Danny’s video:
Find out if the air purifier you want is powerful enough for your space
If you’ve been researching air purifiers for a while, you’re likely to have come across the acronym ACH, which stands for Air Changes per Hour.
ACH refers to how many times the air is replaced in a room during one hour of an air purifier running. If you see 4 ACH, for example, it means the air will be fully filtered and replaced with clean air four times an hour.
The minimum number of air changes per hour we recommend is 4.8 ACH, as this is the minimum recommended by AHAM. However, you can amp that up to 5 ACH (following CDC advice for workplaces) or take it up to 6 ACH (as recommended by ASHRAE for schools).
We created another calculator so you can find out whether the air purifier you want will be able to offer enough air changes per hour in the space where you want to place it.
Simply fill in the CADR of the unit you’re looking to purchase and our tool will tell you what is the maximum size of the room it can clear based on the specific number of air changes per hour that you want to get — the calculator uses 4.8 ACH as standard:
Common questions about choosing the right size of air purifier
Yes, it can. Both in size and power.
If you have limited space in your room, the last thing you want to do is waste it on an unnecessarily big air purifier. Plus, having a large device in a small room can be a giant waste of energy and you’ll be subjecting yourself to expensive long-term running costs when a smaller, less powerful unit will do the ideal job.
That is why looking at the CADR of an air purifier over its sheer size is a better way to go about it.
Having multiple air purifiers can be the most cost-effective choice for very large spaces.
But before you decide, ask yourself the following questions:
- Is there an air purifier capable of cleaning your whole room based on your CADR calculations?
- Do you suffer from severe allergies?
- Is your home located in an area susceptible to wildfire smoke?
- Do you live in an area with severe air pollution?
If you couldn’t find a device that can clean the air in your space by itself, then you will definitely need to look at getting more than one unit.
If you suffer from severe allergies or live in an area prone to wildfire smoke/bad air pollution, then choosing to have more than one device in a room will give you the option to ramp up the air cleaning power whenever you need it.
Air purifiers are designed to clean the space they are in, not your whole home.
If your house is prone to pollution e.g. you live next to a busy road or are affected by wildfire smoke, or suffer from bad allergies from pet dander, dust or mold spores, then having an air purifier in every room in your house, will give you the most protection.
Closing thoughts
Not all air purifiers are created equal. To avoid choosing the wrong device for your space, run your own calculations before you settle on a specific model based on the recommended room size stated in the marketing materials or the Amazon listing.
If you have any other questions I haven’t answered in this article or need more help to make a decision over which model you should get, please drop a comment below and I will try to reply as soon as I read it.
