CADR: Understanding the Clean Air Delivery Rate in Air Purifiers

When shopping for an air purifier, you’ll encounter a variety of specifications and acronyms that can be confusing. Among the most important of these is CADR, which stands for Clean Air Delivery Rate. This metric is crucial for understanding how effectively an air purifier cleans the air in a given space. This article will demystify CADR, explain how it’s measured, why it matters, and how to use it to choose the right air purifier for your home.

What is CADR?

CADR is a standardized measurement that indicates how quickly an air purifier can remove specific pollutants from a room. It quantifies the volume of filtered air delivered by an air purifier, typically measured in cubic feet per minute (CFM) in the United States, or cubic meters per hour (CMH) in other regions. The higher the CADR number, the faster the air purifier cleans the air.

CADR ratings are established by the Association of Home Appliance Manufacturers (AHAM) through rigorous, independent testing. A reputable air purifier will have three separate CADR ratings:

• Smoke CADR: Measures the removal rate of fine particles, similar in size to those found in smoke (0.09-1.0 microns). This is often considered the most important rating as it reflects the purifier’s ability to capture very small, harmful particles.
• Pollen CADR: Measures the removal rate of larger particles, typical of pollen (5.0-11.0 microns).
• Dust CADR: Measures the removal rate of medium-sized particles, characteristic of household dust (0.5-3.0 microns).

How is CADR Measured?

AHAM-certified CADR testing involves placing the air purifier in a sealed test chamber of a specific size. The chamber is filled with a controlled amount of the target pollutant (smoke, dust, or pollen). The air purifier is then run on its highest fan speed, and sensors continuously monitor the reduction of the pollutant over a set period. The CADR value is calculated based on the rate at which the pollutant is removed from the chamber, minus the natural decay rate of the pollutant.

It’s important to note that CADR is measured with a new, clean filter and at the highest fan speed. This means real-world performance might vary, especially as filters get dirty or if the purifier is run on lower, quieter settings.

Why Does CADR Matter?

CADR is the most reliable indicator of an air purifier’s actual cleaning power. Here’s why it’s so important:

• Direct Performance Metric: Unlike marketing claims about filtration efficiency (e.g.,

99.97% filtration), CADR tells you how much clean air is actually delivered into your room. A filter might be highly efficient, but if the fan is weak, the overall cleaning rate will be low. * Room Sizing: CADR directly correlates with the size of the room an air purifier can effectively clean. A higher CADR means the purifier can handle a larger room or clean a smaller room more quickly. * Comparison Tool: CADR provides a standardized way to compare the performance of different air purifiers, regardless of brand or design. It allows consumers to make objective decisions based on cleaning power. * Air Changes Per Hour (ACH): While CADR measures the volume of clean air, ACH refers to how many times the air in a room is completely replaced by clean air in one hour. A good rule of thumb for general air quality is 4-5 ACH, and for allergy/asthma sufferers, 5+ ACH is often recommended. CADR is directly used to calculate ACH for a given room size.

How to Use CADR to Choose an Air Purifier

To select the right air purifier, you need to consider both the CADR rating and the size of the room where you plan to use it.

1. Measure Your Room

First, determine the square footage of the room. Multiply the length of the room by its width. For example, a room that is 10 feet by 15 feet is 150 square feet.

2. Apply the 2/3 Rule of Thumb

A common guideline is that the CADR of your air purifier should be at least two-thirds of the room’s square footage. So, for a 150 sq. ft. room, you would look for a purifier with a CADR of at least 100 CFM (150 * 2/3 = 100).

3. Consider Your Needs

• General Air Quality: If you’re looking for general air purification, adhering to the 2/3 rule is a good starting point.
• Allergies/Asthma/Pets: If you have allergies, asthma, or pets, you’ll want a higher CADR to ensure more frequent air changes. Aim for a CADR that matches or exceeds the room’s square footage, or even higher (e.g., 1.5 times the room size) to achieve 5+ ACH.
• Specific Pollutants: While CADR is given for smoke, dust, and pollen, if you have a specific concern (e.g., heavy smoke), prioritize the CADR rating for that pollutant.

4. Don’t Forget Activated Carbon

While CADR focuses on particulate matter, remember that it doesn’t measure the removal of gases or odors. If these are a concern, ensure the air purifier also has a substantial activated carbon filter.

CADR and Room Size Examples

Here’s a general guide for matching CADR to room size for effective air purification:

Note: These are general guidelines. Always check the manufacturer’s recommended room size and CADR for specific models.

Limitations of CADR

While CADR is an invaluable tool, it has some limitations:

• Highest Fan Speed: CADR is measured at the highest fan speed, which is often the loudest setting. In real-world use, you might run the purifier on a lower, quieter setting, which will result in a lower effective CADR.
• New Filter: Testing is done with a new filter. As filters get dirty, their performance can decrease. Regular filter replacement is crucial to maintain the advertised CADR.
• Gases and VOCs: CADR does not measure the removal of gaseous pollutants or VOCs. For these, you need to look for activated carbon filtration.
• Placement: CADR assumes optimal placement in a test chamber. In a real home, furniture and room layout can affect airflow and overall effectiveness.

Conclusion

CADR, or Clean Air Delivery Rate, is the most important metric to consider when purchasing an air purifier. It provides an objective measure of how quickly and effectively a unit can clean the air of common particulate pollutants. By understanding what CADR means, how it’s measured, and how to match it to your room size and specific needs, you can confidently select an air purifier that will genuinely improve your indoor air quality. Remember to prioritize True HEPA filtration for particles and activated carbon for odors and gases, and always factor in filter replacement costs and noise levels for a comprehensive decision. With the right CADR, you’ll be well on your way to breathing cleaner, healthier air.