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Air Purifiers and Air Changes Per Hour (ACH)

Do air purifiers really work? It’s a really common question and we understand why. After all, we’re solving an invisible problem. Sometimes dust is visible when it lands on surfaces or in a column of light like the early morning sun through a window, but a lot of the particles a high quality air purifier can help with aren’t visible in the air. We can certainly feel them affecting our health though.

Fortunately, there are a few key ways of measuring an air purifier’s performance and how they stack up to the competition. One of these measures is described in air changes per hour, or ACH.

Air changes per hour refers to how often the entire volume of air in a given space is recirculated and changed with new filtered clean air. 

If you’ve been looking for an air purifier you’ve probably seen several variations of air changes per hour. Companies will typically list 2 or 5 air changes per hour, but some only list 1 air change per hour. It’s a potentially overwhelming and confusing, but important, measure of performance. 

Let’s clear the air on what air changes per hour (ACH) means and what you need to look for when researching air purifiers. 


Researching Air Purifiers and Air Changes Per Hour 

Understanding the air changes per hour is essential to truly understand the air cleaning power of a purifier. That’s because in order to truly benefit from an air purifier, you’re going to want it to fully clean the air in your space rather than struggling to clean a space that’s much larger than what it’s designed to handle.

A company should provide 5 air changes per hour square footage information (which, confusingly, is more like 4.8) and share their official clean air delivery rate (CADR) numbers. It’s the easiest way for customers to be able to understand if an air purifier will clean a space their size.

For example, if you have a 300 square foot bedroom, you need to find an air purifier with a smoke CADR of at least 200 to clean the entire area with 5 air changes per hour. Our Mod Jr. has a smoke CADR of 234 making it a great purifier for a 300 square foot room because it can clean 363 square feet with 5 air changes per hour. 

Air changes per hour and CADR is measured at the purifier’s highest speed. It’s best to find a purifier that can clean more than what you need because it’s unlikely you’ll be running your purifier on full power constantly. That’s because the highest setting is also be default on every machine the loudest setting as well. 

Be aware that companies can market their air changes per hour differently and it isn’t yet a required standard — so when you go to compare make sure it’s an apples to apples comparison. 

We’ve made a comprehensive table that compares several air purifier brands that’s sorted by value for performance. 


CADR and Air Changes Per Hour

CADR measures an air purifier’s performance at 5 air changes per hour. CADR is the best statistic to look at to understand the overall cleaning power of an air purifier. 

Again, air purifier companies will sometimes only share 1 air change per hour, which is not really that helpful to customers since it inflates the number and makes comparison shopping harder. It makes the numbers look more impressive and like the air purifier can handle a much larger space.

It’s best to know 5 air changes per hour, which is what CADR provides. The Association of Home Appliances Managers (AHAM) is an independent agency that sets standards recognized by government agencies like the EPA and the Department of Energy. And AHAM recommends 5 air changes per hour for healthy indoor air.

The air purifier industry can be confusing and difficult to understand especially when you just want a product that works to safely clean your indoor home. It’s best to look at official agencies like AHAM for information instead of solely relying on information provided by the air purifier company. 

AHAM isn’t sharing information to sell you a product, they’re gathering information to help you make a more informed decision. This independently sourced information is listed on the ENERGY STAR website as well, which has compiled CADR readings for hundreds of purifiers. If a product is not on the website it means that the product was not submitted for CADR testing. And why not? We’ll let you draw your own conclusions on that.

CADR is the most accurate representation of an air purifier’s cleaning ability. CADR measures both the airflow (how many air changes you get based on the size of the room) and filter efficiency (how well it performs at removing different small particles) of a purifier. Learn more about how CADR is measured from AHAM


Oransi Air Purifier ACH

AHAM suggests that 5 (again, it’s technically 4.8 but typically rounded up) air changes per hour is the goal to provide healthy indoor air. Many commercial buildings achieve 3 air changes per hour with their HVAC systems. So, they need to consider having at least 2 more air changes per hour to efficiently clean their air. 

An air purifier can be a helpful supplemental tool for your commercial HVAC system, but residential homes may need more help to achieve the full 5 air changes per hour. This is why it’s important to know how much square footage a purifier can clean with 5 air changes per hour. HVAC filters are mostly for protecting the system itself as it heats or cools the air.

Oransi currently shares both 2 and 5 air changes per hour for all of our products. Only sharing 1 ACH is not an accurate reflection of an air purifier’s true cleaning ability and it’s typically a sign of some creative math. Measuring this way goes against recommended health advice, common industry standards, and makes it seem like an air purifier can effectively clean an area much bigger than it actually can. 

The Mod+ can clean 1,361 square feet with 2 air changes per hour. And the Mod+ can clean 563 square feet with 5 air changes per hour. The official ENERGY STAR Mod+ smoke CADR number is 563, meaning it is guaranteed to clean 563 square feet with 5 air changes per hour. 

We’re big advocates of air purifier companies sharing their CADR numbers because it’s independent and officially sourced information. It allows customers to accurately compare devices without getting bogged down by marketing claims and buzzwords. And, quite simply, it's the right thing to do. 

Oransi will always openly share our CADR performance and not hide behind manipulating our numbers in an attempt to get customers to purchase our products. We want you to be able to easily find the best fit for you and your family. We’re committed to following regulations that put all air purifier companies on equal footing and give customers more accurate information about how to achieve clean and healthy indoor air in their homes.