Alen Air Filter Comparison: Quick Pick Guide for Every Model

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Choosing the correct alen air filter comes down to matching the physical dimensions of your purifier cabinet to the specific indoor airborne irritants in your living or working environment. Purifier owners often struggle to distinguish between the various frame sizes engineered for the BreatheSmart Classic, the mid-sized 45i, and the compact 35i, while simultaneously deciding whether basic fine particulate filtration, targeted pet odor neutralization, or heavy volatile organic chemical absorption is necessary. Installing the wrong size creates unsealed perimeter gaps that allow contaminated air to bypass the filter entirely, whereas selecting an under-specified media layer leaves lingering cooking smoke and organic aromas recirculating through your rooms.

The manufacturer organizes its filter catalog by chassis profile and specialized chemical-adsorption formulas, offering clear tiers for different air quality challenges across the BreatheSmart portfolio. Each purifier generation uses distinct filter cartridges equipped with mechanical True HEPA paper, optional carbon catalyst compounds, or dense granular carbon beds tailored for chemical fumes. Determining which alen air filter to buy requires confirming your purifier model number and auditing your air quality priorities. Just as evaluating a hamilton air filter requires inspecting media layers, choosing the right Alen cartridge ensures balanced airflow resistance and continuous particulate capture.

Criteria matrix What each model in this report is credited with

Rows are the criteria that come up in the pros and cons listed for this lineup. A check means the criterion is named in this report’s write-up of that model; a dash means it is not. Criteria that apply to every model, or to only one, are left out because they separate nothing.

Criterion	Alen 45i Replacement HEPA 8.4/10	Alen Classic Replacement HEPA 9.4/10	45i Replacement Filter for 9.4/10	Alen Classic Replacement HEPA Filter 9.4/10	Alen Classic Replacement HEPA Filter (5) 9.4/10	Alen 35i Replacement HEPA 8.4/10
H13 True HEPA	✓Named	✓Named	Not named	✓Named	✓Named	✓Named
BreatheSmart Classic	✓Named	✓Named	Not named	✓Named	✓Named	Not named
Medical-grade H13	✓Named	✓Named	Not named	Not named	Not named	✓Named
MERV 16 efficiency	Not named	✓Named	Not named	✓Named	Not named	Not named
Pre-filter screen	✓Named	Not named	Not named	Not named	Not named	✓Named
Plastic frame	✓Named	Not named	Not named	Not named	Not named	✓Named
Living rooms	Not named	✓Named	Not named	Not named	Not named	✓Named
Heavy smoke	Not named	✓Named	Not named	Not named	✓Named	Not named
Criteria named	5 / 8	6 / 8	0 / 8	3 / 8	3 / 8	5 / 8

Built from the wording of this report, not from a bench test. A dash is not a fault: it only means the write-up does not mention that point for that model. Scores next to each model are out of 10, based on listed specifications and buyer feedback.

Alen Air Filters Lineup at a Glance

The Models in Detail

Alen 45i Replacement HEPA Filter

Best for: BreatheSmart 45i owners needing deep odor control

Pros

• Medical-grade H13 HEPA
• 12 to 15 month lifespan
• Vacuumable pre-filter screen
• Gasketed leak-free frame

Cons

• Fits 45i chassis only
• Single-pack replacement

The Alen 45i Replacement HEPA Filter, identified under model number B4-CC-Odor-RFID and formerly designated as the B4, is an authentic OEM replacement cartridge built specifically for the BreatheSmart 45i air purifier. This unit features a slide-in mounting design measuring 15.5 inches long, 11.75 inches wide, and 2.75 inches thick, weighing 1.9 pounds. Its filtration core utilizes medical-grade H13 True HEPA media that captures 99.9% of airborne particles down to 0.1 micron. Backing the particulate layer is an integrated carbon catalyst odor neutralizer formulated to trap and decompose pet smells, diaper odors, and stubborn domestic scents. A vacuumable, easily removable pre-filter screen catches larger fluff and dander before they penetrate the pleated core, while an airtight plastic frame lined with perimeter gaskets prevents bypass leaks.

This alen 45i replacement hepa filter is engineered for busy homeowners and professionals running a BreatheSmart 45i in master bedrooms, medium-sized living areas, or home offices where animal smells and fine particulate matter accumulate. Because the listing states a lifespan of 12 to 15 months, it requires minimal ongoing maintenance beyond occasionally running a vacuum wand over the exterior pre-filter screen. The integrated gasketed frame ensures all air drawn into the machine passes directly through both the 0.1-micron HEPA barrier and the carbon catalyst layer, making it an effective choice for asthma-conscious spaces.

This model gives way to other choices if your purifier is from the larger BreatheSmart Classic series, as the physical 15.5 by 11.75-inch slide-in dimensions will not seat properly in the Classic cabinet. Furthermore, users operating the 45i in clean, low-odor environments who prefer multi-pack consumables with independent pre-filter change schedules might consider third-party alternatives. For genuine maintenance of an alen breathesmart 45i filter system demanding comprehensive odor destruction, this OEM cartridge serves as the primary factory baseline.

Alen Classic Replacement HEPA Filter

Best for: Large living spaces facing smoke and VOCs

Pros

• CARB certified
• Formulated for heavy smoke and VOCs
• Inhibits mold spore growth
• Up to 12 months performance

Cons

• Heavier than standard Fresh filter
• Fits BreatheSmart Classic only

Best for: BreatheSmart Classic homes tackling severe pet odors

Pros

• MERV 16 efficiency rating
• Molecular odor-absorbing compound
• Cleans 1,100 sq ft every 30 mins
• Up to 12 months filter life

Cons

• Heavier 3.5-pound weight
• Chassis limited to Classic model

Best for: BreatheSmart Classic owners managing everyday household dust

Pros

• Cleans 1,100 sq ft in 30 mins
• Medical-grade H13 layer
• Scrubs light smoke and VOCs
• Certified frustration-free

Cons

• Bulky 17-inch frame
• Not designed for heavy smoke

The Alen Classic Replacement HEPA Filter, carrying part number BF35-Silver-Carbon and sold under the Fresh designation, is a genuine replacement cartridge engineered exclusively for the full-sized Alen BreatheSmart Classic purifier. Sized at 17 by 15 by 3 inches and weighing 2.6 pounds, this large-format filter supports the Classic unit’s rated capacity to scrub 1,100 square feet of indoor air every 30 minutes. Its structure incorporates a medical-grade H13 True HEPA layer that captures 99.9% of airborne particles larger than 0.1 micron (with the listing description noting 99.99% capture efficiency for microscopic allergens). An activated carbon layer is embedded into the core to scrub airborne volatile organic compounds, seasonal pollen, animal dander, and lighter ambient smoke.

This configuration suits property owners seeking an all-around alen breathesmart classic filter for large open-concept living rooms, high-traffic commercial waiting areas, and broad professional suites. It handles general ambient dust, seasonal plant allergens, and mild household cooking smells without restricting the high airflow required to cycle an expansive room twice every hour. The listing specifies certified frustration-free packaging and an operating lifespan of up to 12 months under continuous residential use.

This model yields to specialized siblings in the Classic lineup when air contamination shifts toward intense chemical solvents or heavy wildfire soot. While the Fresh filter handles light smoke and everyday odors, environments facing heavy kitchen searing or nearby industrial off-gassing require specialized carbon blends. In properties where clean air maintenance extends to vehicles and indoor spaces, comparing installations with a purolator cabin filter illustrates how tailored carbon density directly governs molecular gas adsorption.

45i Replacement Filter for Alen BreatheSmart

Best for: Budget-focused BreatheSmart 45i and Flex users

Pros

• Includes 2 HEPA and 4 carbon pre-filters
• FSC-certified paper construction
• Tool-free easy installation
• Captures 99.97% of 0.3-micron particles

Cons

• Non-OEM third-party product
• Shorter 6-8 month HEPA lifespan

The 45i Replacement Filter for Alen BreatheSmart is an aftermarket replacement manufactured by Borgodf, designed for compatibility with both the Alen BreatheSmart 45i and BreatheSmart Flex Bh400 purifiers. Packaged as a 6-pack consumable kit, the bundle includes 2 True HEPA filters and 4 separate activated carbon pre-filters. The HEPA elements are constructed from FSC-certified paper and capture 99.97% of airborne particles as small as 0.3 microns, including lint, hair, pollen, and pet dander. The supplementary activated carbon pre-filters fit directly over the main filters to capture cooking fumes, pet dander, and household odors while shielding the pleated media from premature lint saturation. The assembly measures 14.06 by 10.98 by 1.97 inches and weighs 2.35 pounds.

This multi-pack arrangement suits budget-conscious users, facility operators, and multi-pet households operating either a BreatheSmart 45i or a Flex Bh400 purifier who prefer frequent pre-filter changeouts. The listing explicitly states that replacing this 45i filter requires no tools, recommending that the activated carbon pre-filters be changed every 3 to 6 months while the main True HEPA filters run for 6 to 8 months. Having extra pre-filters on hand makes it practical to swap out grease- or hair-laden outer wraps without discarding the underlying pleated HEPA filter prematurely.

This aftermarket set gives way to genuine Alen units for shoppers who demand factory H13 medical-grade filtration down to 0.1 microns, integrated RFID tracking chips, or single-cartridge 15-month replacement cycles. The listing states that this product is not an OEM component and is not covered by any OEM manufacturer warranty. Comparing multi-stage configurations against other brands like a hepa filter air purifier holmes setup confirms that third-party multi-packs prioritize frequent, modular surface changes over thick single-block longevity.

Alen Classic Replacement HEPA Filter

The Alen Classic Replacement HEPA Filter, cataloged under model number BF35-MP and designated as the Odor formulation, is an authentic OEM cartridge tailored for the BreatheSmart Classic air purifier. Weighing 3.5 pounds and carrying an official MERV 16 efficiency rating, this cartridge is purpose-built to cycle 1,100 square feet of air every half hour. The media combines an H13 True HEPA barrier—certified to trap 99.9% of microscopic allergens and pollutants down to 0.1 micron—with a proprietary odor-absorbing compound designed to neutralize unpleasant organic smells at the molecular level. It carries a 1-year EU spare part availability rating and up to 12 months of active filter life.

This specialized alen hepa odor filter is the definitive choice for homes with multiple indoor pets, active nurseries, or residences dealing with strong kitchen aromas such as fried fish and spices. Standard carbon filters rely on basic surface adsorption, but the BF35-MP utilizes molecular odor-destroying compounds to actively break down volatile organic scents from pet accidents, litter boxes, and cooking grease. Allergy sufferers in pet-heavy homes benefit from the MERV 16 rating, which reliably pulls microscopic dander, dust mite feces, and pollen out of expansive living rooms.

The Odor model gives way to the VOC/Smoke variant if your dominant air quality threat consists of volatile organic chemical off-gassing, synthetic building fumes, or persistent wildfire smoke. It also cannot be installed in 45i or 35i purifier chassis due to the much larger Classic frame footprint. However, for pet-related indoor air problems in large spaces, this cartridge provides the heaviest organic odor defense in the Classic family.

Alen Classic Replacement HEPA Filter

The Alen Classic Replacement HEPA Filter, carrying part number BF35-VOC, is an OEM replacement cartridge engineered for the BreatheSmart Classic purifier, optimized specifically for volatile organic compounds and smoke abatement. Measuring 17 by 15 by 3 inches and weighing 3 pounds, this cartridge is certified by the California Air Resources Board (CARB) and cleans 1,100 square feet every 30 minutes. Its filtration assembly integrates an H13 True HEPA mechanical layer that removes 99.9% of particles larger than 0.1 micron alongside a heavy bed of activated carbon. The carbon media is formulated to capture complex chemical fumes, prevent mold spore proliferation across the filter bed, and clear smoke particles.

This model is the best alen air filter for smoke and chemical vapors, making it essential for households in active wildfire zones, properties adjacent to busy highways, or homes undergoing remodeling with fresh paint and adhesive off-gassing. The dense carbon structure provides the necessary dwell time and contact area to trap gaseous hydrocarbons, toxic combustion byproducts, and cooking smoke before air is returned to the room. The listing specifies that this cartridge delivers up to 12 months of clean air performance under standard operating schedules.

This VOC and smoke configuration steps aside for the standard Fresh or Odor editions when chemical fumes and combustion byproducts are absent from your indoor environment. For everyday dust, pollen, and basic dog dander, the specialized chemical-adsorption bed adds unnecessary weight without tangible benefit. Just as selecting a wix cabin filter requires matching vehicle media to dust versus industrial exhaust, selecting this filter makes sense primarily when gaseous chemical exposure or heavy smoke is your verified indoor problem.

Alen 35i Replacement HEPA Filter

Best for: BreatheSmart 35i nursery and small bedroom setups

Pros

• Compact gasketed plastic frame
• H13 True HEPA down to 0.1 micron
• 12 to 15 month lifespan
• Easily removable vacuumable pre-filter

Cons

• Engineered strictly for 35i purifier
• Not suited for large open living rooms

The Alen 35i Replacement HEPA Filter, identified by model number B3-Odor-RFID and formerly labeled as the B3, is a genuine OEM replacement cartridge built exclusively for the compact BreatheSmart 35i air purifier. Measuring 14.2 inches high, 11.1 inches wide, and 1.5 inches thick with an item weight of 1.85 pounds, this unit is engineered to deliver leak-free performance within smaller footprints. It features a medical-grade H13 True HEPA filter that eliminates 99.9% of airborne particles down to 0.1 micron, backed by an integrated odor neutralizer designed to eliminate diaper odors, litter smells, and pet dander. The assembly includes a vacuumable, removable pre-filter screen and a rigid plastic frame backed by perimeter sealing gaskets to ensure optimal airflow without internal air bypassing.

This alen 35i replacement hepa filter is tailor-made for smaller spaces, including nursery rooms, guest bedrooms, and private executive offices where the compact BreatheSmart 35i purifier is installed. The 12 to 15-month operational lifespan matches the extended duty cycles of the larger 45i OEM filters, freeing users from frequent maintenance routines. Regularly cleaning the removable pre-filter screen with a household vacuum maintains steady airflow resistance and extends the service life of the inner pleated media.

This model yields immediately if your home utilizes the 45i, Flex, or Classic purifiers, as its slim 1.5-inch depth and 14.2-inch height will not seal inside larger Alen chassis. Conversely, attempting to use larger filters in a 35i purifier is physically impossible. When your air purification needs are centered in a dedicated bedroom or nursery running a BreatheSmart 35i, this cartridge is the exact factory-specified fit.

Matching a Model to Your Setup

• For intense wildfire smoke, heavy cooking searing, or post-painting chemical fumes in a large room: Install the Alen Classic Replacement HEPA Filter (VOC/Smoke, BF35-VOC) to leverage its CARB-certified activated carbon bed.
• For persistent pet odors, multiple litter boxes, or diaper smells in a wide open floor plan: Choose the Alen Classic Replacement HEPA Filter (Odor, BF35-MP) with its molecular odor-destroying compound and MERV 16 efficiency.
• For general pollen, everyday house dust, and light seasonal odors in a large living area: Fit the Alen Classic Replacement HEPA Filter (Fresh, BF35-Silver-Carbon) into your BreatheSmart Classic machine.
• For complete allergen defense and odor neutralization in a master bedroom running the 45i: Select the genuine Alen 45i Replacement HEPA Filter (B4-CC-Odor-RFID) with gasketed borders and a 15-month lifespan.
• For high-dust or pet-heavy rooms where you want frequent, low-cost pre-filter swaps on a 45i or Flex: Use the Borgodf 45i Replacement Filter for Alen BreatheSmart 6-pack to take advantage of four separate carbon pre-filter wraps.
• For nurseries, home offices, or small bedrooms using the compact 35i chassis: Equip the purifier with the Alen 35i Replacement HEPA Filter (B3-Odor-RFID) for airtight 0.1-micron particle capture.

Before You Buy

When conducting an alen air filters comparison, verify the physical dimensions and exact chassis designations of your air purifier before ordering. The product listings confirm that Alen replacement filters are strictly chassis-specific; a BreatheSmart Classic cartridge measuring 17 by 15 inches cannot be cut down or retrofitted into a BreatheSmart 45i or 35i unit. Furthermore, while genuine OEM listings explicitly advertise medical-grade H13 True HEPA performance capable of capturing 99.9% of particles down to 0.1 micron, third-party aftermarket listings specify 0.3-micron particle capture at 99.97% efficiency using FSC-certified paper. Be sure to confirm whether your priority is ultra-fine 0.1-micron filtration or multi-pack value with independent pre-filter layers.

The product listings do not include replacement installation tools or separate mounting brackets, as every Alen purifier relies on tool-free slide-in rails or snap-fit compartments. It is also important to note that OEM models featuring RFID designations communicate directly with electronic purifier consoles to monitor operating hours, a feature the listings do not specify for third-party aftermarket clones. Finally, the manufacturer listings note that genuine Alen warranty coverage applies only to purifiers used within the contiguous United States, while non-OEM replacement units carry no OEM manufacturer backing.

FAQ

How do I know which alen air filter to buy for my machine?

Check the product label located on the rear or underside of your air purifier to identify your exact machine chassis. Classic filters fit only the BreatheSmart Classic cabinet, 45i filters fit the BreatheSmart 45i (and certain compatible options fit the Flex Bh400), and 35i filters fit only the BreatheSmart 35i. Once the chassis size is confirmed, choose between Fresh, Odor, or VOC/Smoke media based on whether your primary concern is dust, pet smells, or chemical fumes.

How often should an alen replacement filter be swapped out?

According to the product listings, authentic Alen 45i and 35i OEM filters have an extended operational lifespan of 12 to 15 months. Genuine BreatheSmart Classic filters specify up to 12 months of pure air production under typical household use. For third-party consumable kits like the Borgodf 6-pack, the listing recommends replacing the primary True HEPA filters every 6 to 8 months and replacing the carbon pre-filters every 3 to 6 months.

Can I wash my Alen replacement filter with water?

The listings do not specify water washing for any of these pleated HEPA filters or carbon layers, and wet cleaning can damage the structural paper fibers and deactivate carbon media. However, the OEM 45i and 35i listings explicitly highlight a removable pre-filter screen that can be easily cleaned using a household vacuum cleaner to remove surface lint and preserve airflow efficiency.

What is the difference between an Odor filter and a VOC Smoke filter?

The Alen Classic Odor filter (BF35-MP) incorporates a proprietary molecular odor-absorbing compound specifically formulated to destroy organic household smells, such as pet odors, litter boxes, and diaper bins, alongside a MERV 16 particle rating. The VOC/Smoke filter (BF35-VOC) features CARB certification and a heavy activated carbon bed engineered to trap gaseous chemical fumes, paint off-gassing, toxic combustion byproducts, and wildfire smoke.

Does a compatible non-OEM filter fit both the Alen BreatheSmart 45i and Flex?

Yes, the Borgodf replacement filter listing specifically states compatibility with both the Alen BreatheSmart 45i and the BreatheSmart Flex Bh400 purifiers, sharing dimensions that replace part numbers B4-Fresh, B4-Pure, and FL40-Silver-Carbon without requiring any installation tools.