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A Corsi-Rosenthal Box is a do-it-yourself air cleaner made from a box fan and HVAC filters. A common four-filter version uses four MERV 13 filters, a cardboard base and tape. Correct filter orientation and sealed joints matter: gaps can let air bypass the filter media. It can reduce airborne particles, including wildfire smoke, but its performance depends on the build and it does not guarantee clean air or prevent infection.
What a Corsi-Rosenthal Box isโand what it is not
The design draws room air through multiple filters and pushes the filtered air back into the room with a box fan. UC Davisโs four-filter guide uses four MERV 13 filters arranged around the fan, with cardboard forming the base and duct tape sealing the joints.
It is a DIY particle air cleaner, not a HEPA-certified appliance. EPA describes DIY air cleaners as a temporary alternative when air cleaners with known performance are unavailable or unaffordable. Evidence supports particle reduction from well-built units, but no box should be treated as a guarantee against infection or as a substitute for other protective measures.
Choose the fan and filters before assembling
- Fan: EPA recommends a box fan made in 2012 or later that carries a UL or ETL safety logo. Follow the fanโs instructions; do not assume an older or uncertified fan has known safety performance.
- Filters: EPA recommends a high-efficiency filter rated MERV 13 or higher, sized and shaped to fit the fan configuration. Its simple one-filter example uses a 20 ร 20-inch fan and a similarly sized HVAC filter; this is an example, not a universal fit guarantee.
- Thickness and count: EPA says filters 2โ4 inches thick rather than 1 inch, and multiple-filter designs, can improve CADR. They also take more space and materials.
- Other supplies: The UC Davis four-filter example uses four 2-inch MERV 13 filters, cardboard from the fan carton for the base, and duct tape. EPAโs one-filter version uses a shroud and tape, clamps or bungee cords.
Filter thickness and the exact fan arrangement in the UC Davis example are not requirements for every DIY design. Check dimensions and airflow direction for the components you have. EPAโs guidance says: โTo maximize filtration, choose a high-efficiency filter, preferably rated Minimum Efficiency Reporting Value (MERV) 13 or higher, that is the same size and shape as the fan.โ See EPAโs DIY air-cleaner guidance.
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#1 Best Overall
AirFanta 3Pro, Air purifer for house up to 3100ft2, CADR super large 413cfm, collapsible and portable, can be packed into a 20" suitcase.
- INNOVATIVE DESIGN: The AirFanta 3Pro features an unique, minimalist design without a casing or screen, but elevating purification speed, portability, and affordability to new heights.
- HIGH PERFORMANCE: Due to the four powerful PC fans and massive amount of EPA filters used, the 3Pro has a very high Clean Air Delivery Rate (CADR) โ 413 cubic feet per minute. It can purify the air of a 3,100 square-foot room once in one hour. A 517 square-foot room will be cleaned six times in one hour. The 3Pro outperforms most other home air purifiers in speed, while maintaining a low noise level ranging from 25 dB to 55 dB. Itโs ideal for large rooms, classrooms, hotel stays, and homes alike.
- COLLAPSIBLE AND PORTABLE: With its innovative design, the AirFanta 3Pro can be assembled and disassembled in just one minute. When assembled, it has a compact footprint of only 1 square foot and weighs just 7 lbs. Disassembled, it fits easily into a 20-inch carry-on bag, making it perfect for travel.
- HEPA FILTERS: The device features four filter panels with a total of 43 square feet of HEPA filtration. These filters offer a high filtration efficiency of 99.5% for particles as small as 1 micron and 95% for particles of 0.3 micron, while maintaining a low pressure drop. This ensures exceptional Clean Air Delivery Rate (CADR) performance. This model equips with HEPA and doesn't contain carbon. If you are looking for carbon to absorb odor or VOCs, we have the model equipped with HEPA + Carbon filters, which can be found in our store.
- CERTIFIED: This edition is UL507 certified by SGS in both the US and Canada, guaranteeing electrical safety and high quality. It is also CARB certified to meet the necessary requirements in California.
How to build the four-filter version
- Arrange the filters around the fan. Make the four filters form the sides of a box, with the fan on top and the open bottom ready to be capped by cardboard. Check each filterโs airflow arrow: air should be drawn from the room through the filters toward the fan.
- Seal the filter joints. Tape the vertical seams between filters so air is less able to leak around the media.
- Make and attach the base. Cut cardboard to cover the open bottom and tape it securely to the filter edges. The base helps direct incoming air through the filters rather than from an unfiltered opening.
- Seal the fan-to-filter connection. Attach the fan to the top opening and tape gaps between the fan and filters. The goal is to reduce bypass airflow while leaving the fanโs intake and outlet unobstructed.
- Check stability and placement. Set the assembled unit on a stable surface where it will not be bumped or create a trip hazard. Operate it according to the fan manufacturerโs instructions.
For the exact illustrated arrangement and details, use the UC Davis assembly guide. EPA also describes a simpler one-filter cleaner with a cardboard shroud in its DIY air-cleaner instructions.
How much air cleaning can it provide?
EPA reports wildfire-smoke clean air delivery rate (CADR) measurements for specific tested DIY configurations. CADR represents the volume of filtered air delivered. In EPAโs reported tests, the four-filter Corsi-Rosenthal Box configuration had a higher wildfire-smoke CADR than the listed one-filter designs:
Rank #2
3Pro Air Purifier for Large Homes up to 3400ftยฒ
- Powerful Air Purification: With a high CADR of 440 cubic feet per minute, air purifier purifies the air of a 3,400 sq.ft. room once per hour, ensuring a healthy environment.
- Adjustable Noise Levels: The air purifier's adjustable fan speed means it's as quiet as 36 decibels on the lowest level, and creates helpful white noise on higher settings.
- Portable Design: The collapsible and portable Corsi Rosenthal filter makes air purifier easily transportable, perfect for people who travel frequently.
- Effective Filters: Our air purifier provide efficient filtration of harmful particles, and only need to be replaced every 6-12 months depending on usage.
- Convenient Replacement Filters: Our air purifier has ensured easy filter replacements with continuous availability, offering a choice of regular HEPA or activated charcoal HEPA filters.
| EPA-tested configuration | Wildfire-smoke CADR reported |
|---|---|
| One 1-inch MERV 13 filter | 111 ยฑ 1 |
| One 1-inch MERV 13 filter with cardboard shroud | 156 ยฑ 4 |
| One 4-inch MERV 13 filter with cardboard shroud | 248 ยฑ 15 |
| Two 1-inch MERV 13 filters with cardboard shroud | 263 ยฑ 22 |
| Four 1-inch MERV 13 filters in a Corsi-Rosenthal Box with cardboard shroud | 401 ยฑ 31 |
These are results for EPAโs tested wildfire-smoke configurations, not guaranteed ratings for every homemade unit, room or operating condition. EPAโs summary says a cardboard shroud raised CADR by 40% in its one-filter comparison without changing cost or footprint. More filters improved particle removal in the tested designs, while adding material cost, assembly complexity and space needs. The consulted EPA summary does not state a publication year for these figures. See EPAโs DIY air-cleaner wildfire-smoke results.
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Bestseller No. 1
Bestseller No. 2
Best Value
Sale
KOIOS H13 True HEPA Air Purifier for Home Bedroom 2500 sq ft, Carbon Filter
- Powerful Large-space Purification Capacity: The KOIOS air purifier is engineered specifically for use in large areas of your home. As a powerful air purifiers for home, it delivers an effective airflow of 2,500 square feet per hour, rapidly circulating and cleaning the air in living rooms, large bedrooms, garages, offices, classrooms, gyms, and dance studios. The hepa air purifier brings fresh air into your home and refreshing every corner of the space.
- PM2.5 Real-Time AQI + Auto Mode: This air purifier large room features a PM2.5 sensor, a large display and a 4-color indicator, giving you immediate air quality data so you always know indoor conditions. Auto mode adjusts fan speed automatically based on live readings โ less guesswork, more confidence. Whether cooking in the kitchen, playing with pets, or putting kids to sleep โ Auto mode detects pollution and adjusts speed instantly.
- Washable Pre-filter & Filter Replacement Indicator: The washable pre-filter can be rinsed to cut replacement filter costs. This true H13 HEPA air purifier with activated carbon filter targets dust, dander, smoke, and smells. If you need air purifiers for home pets or to reduce secondhand smoke, KOIOS AP2503 air purifier is your ideal choice. Note: the filter change light reminds you every 3-6 months, then you could search for B0GTPP3KBR to get genuine filters.
- Sleep Mode, Display Off, 1-12h Timer Setting: The air purifiers for bedroom use feature ultra-quiet operation and customizable controls. With a one-touch Sleep mode, noise drops to as low as 20 dB, perfect for light sleepers and nursery use. The 4-speed fan, "Display Off" feature, and 1โ12 hour timer setting give you complete control over operation. Put your child to bed, tap Sleep mode, and set the timer for 8 hours. The air cleaner runs quietly through the night and auto-off after wake-up. Clean sleep air, zero disturbance.
- Thoughtful, Easy-Use Design & Safety Certifications: Every detail is designed for real-life homes. Child Lock, anti-skid pads + rounded corners are friendly for kids, while the removable aroma clip comes with 5 extra pads for a touch of essential oils. A hidden carry handle makes it easy to move between rooms. Quick-swap filter access and an easy control panel make maintenance effortless. Beyond design, this air purifiers for home meet FCC, EPA, CARB, and DOE standards for safety and energy compliance โ so you can breathe easy.
Rank #4
Sale
VEWIOR Air Purifiers with Washable Filter for Home Large Room Up to 3000ftยฒ
- ใWashable Filter Saves Your MoneyใThe air purifier with washable filter features a complete 3 โ stage purification system โ including a pre washable filter, H13 True HEPA, and activated carbon filter. Simply rinse the preโfilter clean and reuse it, which dramatically extends service lifespan. Compared to ordinary air purifiers, you don't need to replace the air filters frequently. The long-term usage cost is much lower.
- ใHigh Filtration Efficiency & WholeโRoom CoverageใWith a powerful motor, this air purifier for large room providing rapid air circulation to refresh up to 3000 ftยฒ per hour, effectively captures 99.97% of particles like smoke, pet hair, PM2.5 and dander.etc. Whether in your bedroom, living room, office, basement, or kitchen, it ensures fresh air reaches every corner, perfect for large rooms.
- ใRealโtime PM2.5 Display & Smart Auto ModeใThe home air purifier features digital PM2.5 reading gives you the exact particle count in real time. Watch the air quality indicator light as air quality changes โ a quick glance tells you if itโs clean (green), moderate (yellow), or poor (red). In auto mode, the purifier senses air quality in real time and adjusts fan speed automatically, so you get optimal performance without lifting a finger.
- ใWhisperโQuiet Sleep Mode & OneโTouch Light OffใThis air purifier for bedroom operates at an ultraโlow 15dB, keeping noise to a minimum for peaceful rest. In sleep mode, all indicator lights automatically turn off after 10 seconds (you can also press to turn off instantly), creating total darkness that's perfect for lightโsensitive sleepers, babies, or anyone who needs uninterrupted deep sleep.
- ใ4 Timer & Child LockใSet the timer to shut off after 1, 2, 4, or 8 hours, ideal for setting before bed so you donโt waste energy while sleeping, or for automatically turning off when you leave home. Child lock locks all button, prevents kids or pets from altering your settings. Keep your preferred mode intact, hassleโfree.
Rank #3
Sale
KNKA Air Purifiers for Home Bedroom Up to 1,695 Ftยฒ in 1 Hr, APH4000, White
- ๐๐๐๐ ๐๐๐ซ๐ข๐๐ข๐๐ & ๐๐ข๐ ๐ก ๐๐๐๐ ๐๐๐ฅ๐ฎ๐: Certified by the Association of Home Appliance Manufacturers, this air purifier provides reliable performance with a Smoke/Dust/PM2.5 CADR of 226 CFM (384 mยณ/h) and a Pollen CADR of 244 CFM (415 mยณ/h). AHAM certification guarantees effective, high-speed air purification for your home.
- ๐๐๐๐ข๐๐ข๐๐ง๐ญ ๐๐ข๐ซ๐๐ฅ๐จ๐ฐ ๐๐๐ฌ๐ข๐ ๐ง: Engineered with dual front-and-back air intakes and dual side outlets, this purifier maximizes circulation for faster air exchange. It refreshes the air 4.8 times per hour in rooms up to 350 ftยฒ, reaching up to 80% purification efficiency, while still delivering 1 full air refresh per hour in larger spaces up to 1695 ftยฒ with about 45% efficiency, helping maintain cleaner, fresher air throughout your home.
- ๐๐ฎ๐๐ฅ ๐ ๐ข๐ฅ๐ญ๐๐ซ๐ฌ & ๐-๐๐ญ๐๐ ๐ ๐๐๐ฌ๐ข๐ ๐ง: Equipped with dual front-and-back cartridges, each featuring a three-stage filtration system: a washable pre-filter for larger particles, a High-Efficiency filter, and an activated carbon filter. 3-in-1 filter system traps everything from pet hair to microscopic particles, ensuring thorough purification. (Please remove the filterโs plastic packaging before installation.)
- ๐๐๐ & ๐๐๐ ๐๐จ๐๐๐ฌ: PET Mode increases airflow to tackle pet hair, dander, and odors, refreshing the air in just 30 minutes. ECO Mode saves energy and extends filter lifespan by entering standby when air quality is excellent, then restarting automatically when purification is required.
- ๐๐ฎ๐ฅ๐ญ๐ข๐ฉ๐ฅ๐ ๐๐จ๐๐๐ฌ & ๐ ๐๐ง ๐๐ฉ๐๐๐๐ฌ: Includes Sleep Mode with noise levels as low as 22-24 dB for ultra-quiet nights, Auto Mode for effortless adjustments, and four fan speeds for personalized comfort. Select the setting that suits your needs any time of day.
Use it sensibly and maintain it
- Keep the fan unobstructed and place the unit where it cannot be easily knocked over or tripped over.
- Inspect filters and replace them when dirty, following the relevant build guidance and filter instructions.
- Do not infer a specific room-level result from EPAโs laboratory CADR figures; they describe tested configurations, not every home installation.
- For wildfire smoke, use the box as one particle-reduction measure rather than a promise that indoor air is pollutant-free. EPA discusses indoor filtration and clean-room steps in its air-cleaner and HVAC filter guidance and wildfire clean-room guidance.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
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