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Selecting the appropriate air purifier capacity is essential to ensure optimal air cleaning and address your specific needs. Factors such as room size, pollution levels, and specific health concerns should be taken into account. By considering these factors, you can choose an air purifier that matches the size of your room, effectively targets pollutants, and meets your desired air quality goals. However, it's important to avoid common pitfalls like underestimating room size or overemphasizing higher capacity. In this article, we provide useful tips to help you navigate the process of selecting the right air purifier capacity for your unique requirements.

  1. Room Size: Measure the square footage of the room accurately. Choose an air purifier with a coverage area that matches or slightly exceeds the room's size to ensure efficient air cleaning.
  2. Pollution Level: Consider the specific air quality issues you're dealing with. If you live in an area with high outdoor pollution or have indoor sources like pet dander or cooking odors, opt for an air purifier with a higher CADR rating and CFM to handle the increased pollutant load.
  3. Specific Health Concerns: If you have specific health concerns such as allergies or asthma, look for air purifiers that target those allergens or irritants. For example, air purifiers with HEPA filters are effective for capturing allergens like pollen, dust mites, and pet dander.

While choosing the right air purifier capacity, be mindful to avoid the following pitfalls:

  1. Underestimating Room Size: Avoid selecting an air purifier with a coverage area significantly smaller than your room size. This can compromise the purifier's effectiveness and may not provide adequate air cleaning.
  2. Underestimating Capacity: We recommend selecting an Alen air purifier that has twice the capacity you need. This way, you can run the unit on medium speeds (2 or 3) and still keep you noise levels reasonable for conversations or watching TV etc. At times when you need significant cleaning power, a larger capacity unit will enable you to clean your air quickly so you can return to lower speeds so it is livable.
  3. Ignoring Specific Air Quality Concerns: It's essential to identify and address your specific air quality concerns. Consider the specific pollutants or allergens you want to target for optimal purification. Alen has 4 different types of filtration technologies to serve your diverse needs. Pure filter: Good For: Capturing allergens, dust, mold, and germs. Fresh filter: Good For: Absorbing harmful chemicals and VOCs, cooking odors, and common household odors + capturing allergens, dust, mold, and germs. VOC/Smoke Filter: Good For: Absorbing noxious gases from wildfire smoke and secondhand smoke, harmful chemicals and VOCs + capturing allergens, dust, mold, and germs. Odor Filter: Good For: Neutralizing pet, diaper, and other stubborn household odors + capturing pet dander, allergens, dust, mold, and germs
  4. Neglecting Noise Considerations: Keep in mind that some brands of air purifiers may generate more noise, especially when running at higher speeds. If noise is a concern, strike a balance between capacity and noise level to ensure a comfortable and quiet environment.

By carefully considering room size, pollution levels, and specific health concerns, you can select an air purifier with the appropriate capacity to effectively improve indoor air quality and address your specific needs.

Understanding Room Size and Air Purifier Coverage

Air purifiers work by drawing in air from your room, passing it through a series of filters to remove contaminants, and then releasing the cleaned air back into the room. The efficiency of this process is influenced by the size of the room.

In a small room, an air purifier can cycle through the total volume of air more frequently, resulting in more effective and quicker air purification. Conversely, in a larger room, the air purifier has more air to clean, which can slow down the purification process. Therefore, it's essential that the air purifier is appropriately sized for the room to ensure it effectively and efficiently removes airborne pollutants.

Importance of Understanding the Size of the Room When Choosing an Air Purifier

Knowing the size of your room is critical in choosing an air purifier because air purifiers are designed to clean the air in a specific amount of space. Each air purifier has a 'coverage area' specification, often measured in square feet, which indicates the maximum room size for effective operation.

How to Measure a Room for an Air Purifier

To determine your room size, you'll need to measure the length and the width of your room in feet. Multiplying these two measurements will give you the total square footage of the room, which is the standard measurement used in air purifier coverage areas.

For example, if your room is 12 feet wide and 15 feet long, your room's total size is 180 square feet (12*15). It's important to note that if the room is not a perfect rectangle, you may have to break it down into smaller rectangles and add their areas together. Thus for a 180 sq ft room, we would recommend an Alen air purifier that can cover at least 400 sq ft to meet our noise and livability suggestions.

Additionally, consider the room's height as well. Though less common, some manufacturers also factor in cubic feet (width x length x height) for rooms with exceptionally high ceilings. When manufacturers calculate cubic feet, they are typically assuming a ceiling height of eight feet. Most homes today have much higher ceilings. If you have very high ceilings, we recommend selecting an Alen air purifier that is 3 times the room size to accommodate the increased ceiling heights.

Common Room Sizes in American Homes

The size of rooms can vary significantly in American homes, but the following are some typical dimensions of homes built in the past 20 years:

  1. Living Room: These are typically larger spaces where families gather, ranging from 300 to 600 square feet.
  2. Bedrooms: Master bedrooms often range from 200 to 350 square feet, while other bedrooms can range from 100 to 200 square feet.
  3. Kitchen: Kitchens can vary significantly based on the house's layout, but they generally range from 100 to 200 square feet.
  4. Dining Room: These spaces usually range between 150 to 250 square feet.
  5. Home Office: Many modern homes have a dedicated office space, typically around 100 to 200 square feet.
  6. Open Concept: These are spaces that combine the living room, dining room and kitchen. These are often about 1000 square feet. We would recommend at least one 75i in the living room and a 45i in the dining room to get adequate coverage.

Matching Common Room Sizes with Appropriate Air Purifier Capacities

Choosing the right air purifier capacity depends on the size of your room and the specific air quality issues you're facing. The following recommendations serve as a general guide:

  1. Living Room: Given their larger size, living rooms usually require air purifiers with a high CADR rating and CFM. Consider an air purifier rated for rooms larger than 300 square feet, with a CADR and CFM to match. For this room, consider the Alen Breathesmart 75i.
  2. Bedrooms: For a typical bedroom of around 150 square feet, consider an air purifier rated for rooms up to 200 square feet, ensuring it has a lower noise level for peaceful sleep. For this room, consider the Alen Breathesmart 45i. For smaller bedrooms like kids rooms, the Alen Flex would be a good option.
  3. Kitchen: Kitchens can benefit from air purifiers rated for 100 to 200 square feet. Given the variety of odors and particles typically present, an air purifier with activated carbon filters would be beneficial here. The Alen 45i works great for kitchens, it’s small and compact but can effectively remove cooking odors.
  4. Dining Room: A medium-sized air purifier, suitable for rooms up to 250 square feet, would generally be a good fit for dining rooms. The Alen 45i also works great for dining rooms.
  5. Home Office: For this typically smaller space, a quieter air purifier rated for rooms up to 200 square feet would be a good choice to maintain a quiet work environment. The Alen Flex is a great option for a home office.

What is CADR and Why It Matters

Clean Air Delivery Rate, commonly abbreviated as CADR, is a metric used to quantify the total volume of air that an air purifier can filter of a specific pollutant in one hour. The measurement is often given in cubic feet per minute (CFM). This standard was developed by the Association of Home Appliance Manufacturers (AHAM) to provide a clear and standardized way to compare the efficiency of air purifiers.

CADR ratings are typically provided for three types of pollutants: tobacco smoke, dust, and pollen, each with a number that indicates how much cubic feet of air per minute it can clean of the specific pollutant. The higher the CADR number, the more air it can filter in a given time, meaning it's more efficient at cleaning the air.

Understanding the CADR rating of an air purifier is crucial because it indicates how effective the purifier will be in your specific environment. If you have a large room, for example, you'll want an air purifier with a high CADR rating, which means it can clean a large volume of air quickly.

How to Interpret CADR Ratings and Apply Them When Selecting an Air Purifier

To make an informed decision when purchasing an air purifier, you need to consider the room size where the purifier will be placed and compare it to the CADR rating of the air purifier.

As a general rule, for optimal efficiency, you want an air purifier with a CADR rating that's at least two-thirds of the room's area in square feet. For instance, if your room measures 150 square feet, an air purifier with a CADR rating of 100 for each pollutant would be suitable.

It's also essential to consider the specific pollutants you wish to remove. If you're primarily concerned about removing pollen, pay more attention to the CADR rating for pollen.

Remember, CADR is just one aspect of selecting an air purifier. While it's an important factor in determining how quickly an air purifier can clean the air in your room, other features and considerations such as the type of filters used, noise level, energy consumption, and cost are also important to consider in your buying decision.

What CFM is and Why It's Important in Air Purification

Cubic Feet per Minute, or CFM, is a measurement of the velocity at which air flows into or out of a space. In the context of air purifiers, it represents the amount of air that can be moved by the purifier's fan within one minute. Essentially, CFM measures the 'power' of the air purifier to draw in and push out air.

Understanding an air purifier's CFM is crucial as it gives an idea of how quickly the air in a room will be circulated and cleaned. A high CFM means the air purifier can process larger volumes of air quickly, making it a good choice for larger rooms or heavily polluted areas. Conversely, a lower CFM might be more appropriate for a smaller room.

How to Interpret CFM Ratings and Their Role in Selecting an Air Purifier

CFM ratings can range significantly depending on the size and power of the air purifier. When looking at CFM, consider the size of your room and the amount of air that will need to be filtered.

Typically, you want an air purifier that can completely circulate the air in the room at least 2-3 times per hour. This means the air purifier's CFM should be sufficiently high to filter the total volume of the room's air (calculated by multiplying the room's square footage by the height of the ceiling) multiple times within an hour.

For example, suppose your room measures 300 square feet with an 8-foot ceiling. The total volume is 2400 cubic feet. If you want the air to be circulated three times per hour, you'd need an air purifier with a CFM rating of at least 200 (2400 cubic feet x 3 / 60 minutes = 120 CFM).

Keep in mind that the CFM advertised by manufacturers is usually measured at the air purifier's highest settings. Real-world CFM might be lower depending on the settings you choose to use and other factors like filter dirtiness. Therefore, it can be beneficial to opt for an air purifier with a slightly higher CFM rating than your calculated needs.

As always, consider other factors like noise levels, energy efficiency, filter types, and your specific air quality needs when selecting an air purifier.

The Role of Noise Levels in Choosing an Air Purifier

The noise level of an air purifier is primarily determined by the fan's speed - the component that drives air through the filters. When the fan operates at higher speeds, it typically generates more noise. Noise levels are measured in decibels (dB), a unit that quantifies the intensity of sound.

Manufacturers usually provide a noise level range for their air purifiers, indicating the minimum and maximum noise output, corresponding to the lowest and highest fan speed, respectively. For example, most air purifiers have a noise level range of 50dB (quiet conversation level) at their lowest setting. Alen designs noise levels of no mre than 49dB at the highest speed. 

The Trade-Off Between Purifier Capacity, Running Speed, and Noise

There's a trade-off between the air purifier's capacity, running speed, and noise level. A larger capacity air purifier with a high CFM rating will clean a large volume of air quickly, but it might also produce more noise, especially if it's running at a high speed. Conversely, a smaller capacity purifier may operate more quietly, but it might not clean the air as efficiently, particularly in larger rooms.

Choosing the right air purifier involves finding a balance between these factors based on your individual needs and preferences. If you're particularly sensitive to noise, for example, you may opt for a quieter model and accept that it may take longer to clean the air.

Why a Bigger Air Purifier Running at a Lower Level Is Preferable

In some cases, choosing a larger capacity air purifier and running it at a lower speed may be the best solution. This is because a larger air purifier can still effectively clean the air in your room while operating at a lower and quieter speed.

This strategy can be especially beneficial in environments where noise is a concern, such as bedrooms or home offices. Running a larger air purifier at a lower speed can keep the noise levels down while ensuring efficient air cleaning. Moreover, running an air purifier at lower speeds can also prolong the lifespan of the fan motor and result in less energy consumption over time.

Remember, the key to selecting the right air purifier is to consider your specific needs - the size of the room, the types of pollutants you need to remove, your noise tolerance, and your energy consumption preferences. Try out the Alen Digital Assistant to help you find the right air purifier for your needs.


Choosing the right air purifier is crucial for effective air cleaning and achieving desired indoor air quality. Understanding the size of your room and selecting an air purifier with an appropriate coverage area ensures that pollutants are efficiently captured and filtered. Proper sizing allows the air purifier to effectively circulate and clean the air in your space, providing you with clean and healthy indoor air.

As you embark on the journey of selecting an air purifier, remember to consider multiple factors beyond room size alone. Take into account the CADR and CFM ratings, which indicate the air purifier's effectiveness in cleaning the air. Additionally, consider the noise levels to ensure a comfortable and peaceful environment. By carefully evaluating these factors, you can make an informed decision and choose an air purifier that aligns with your room size, specific air quality needs, and personal preferences.

Improving indoor air quality is a significant step towards creating a healthier living environment. With the right air purifier capacity, you can effectively tackle airborne pollutants and allergens, making your home a haven of fresh and clean air.

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