How recommended room sizes for air purifiers are calculated

CADR is the most important metric that determines the recommended room sizes for air purifiers. Here's how it is used in the ANSI/AHAM and NRCC formulas.

How recommended room sizes for air purifiers are calculated

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Recommended room size is the specification that serves as a guideline when choosing the air purifier model that suits your room size. Sometimes, more than one number is provided based on the standards adopted by air purifier manufacturers. These standards are used in different countries and are essentially calculated based on the clean air delivery rate (CADR) of the air purifiers.


Developed by the Association of Home Appliance Manufacturers (AHAM) in the United States, Method for Measuring Performance of Portable Household Electric Room Air Cleaners suggests that the recommended room size be determined based on the ability of the air purifier in reducing 80% of the concentration of particulates in the air.

Room size (in m²)=0.085 x CADR (in m³/h)


Developed by the National Research Council Canada (NRCC), Method for Testing Portable Air Cleaners, also recommends that the room size be determined based on the effectiveness of 80% reduction in particulates in the air. However, they also take into account the removal of particulates through deposition and ventilation.

Room size (in m²)=0.26 x CADR (in m³/h)

Which standard should we believe in?

Due to the difference in formula, the recommended room sizes for the same air purifier model can be vastly different. For example, here are the calculations of recommended room sizes for Ionmax Breeze Plus that has a CADR of 255m³/h:

Calculation 0.085 x 255m³/h 0.26 x 255m³/h
Recommended room size 22m² 66m²

Ionmax Breeze Plus has recommended room sizes of 22sqm (ANSI standard) and 66sqm (NRCC standard) based on two different standards.

These numbers can only serve as a reference when it comes to determining the specification of the air purifier model that suits your home, keeping in mind that there are several other factors that can affect the efficiency of air purifiers such as placement, the height of the ceiling, and ventilation. When you are comparing the recommended room size for two different air purifier brands, make sure that both of the brands are using the same standards to ensure a fair comparison.


An air purifier with a smaller recommended room size does not necessarily mean a lower air filtration performance. A lower CADR may be attributed to a more compact HEPA filter that boasts better performance in removing microscopic allergens from the air; hence, it takes more time to force the air through the filter. As a buyer, it’s important to take into account several other specifications, such as grade of the filter and technologies used, to make the most informed decision when choosing a suitable air purifier for your home.

Disclaimer: The information provided in this article is for general reference only. Please seek advice from professionals according to your needs.

Ionmax Australia

Ionmax Australia

Founded in 2003, Ionmax Australia has received numerous awards and accolades for its innovative products and commitment to customer satisfaction. Ionmax dehumidifiers and air purifiers have been recognised for their effectiveness in reducing indoor air pollutants and improving air quality. The company is committed to researching and developing new and improved products that meet the needs and expectations of its customers, making it a trusted name in households across Australia and beyond.

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