The easiest and the cheapest way to purify the room air

youtube https://youtu.be/aVQ_mMCai7c The smoke from California fires caused air purifiers to be sold out at many locations. Today I am going to show you how to use what you have or can probably still get, to the room air clean. Compared with the expensive air purifiers on the market, these DIY air purifiers are equivalent but at a much cheaper price. Three reasons they are cheaper:

if you already own a fan, then you don’t have to buy another fan.
when buying filters, you can buy whatever size is most suitable for your fan, or is cheaper
unlike air purifiers, the filters as well as fans can be bought cheaply (because both items are high volume commodities).

For example both the fans and the filters can be bought for about $15 each. twitter https://twitter.com/RealGeniusAsian/status/1064217360138145793

For the full video tutorial, visit Genius Asian.

Alternative Methods

The cheapest DIY air purification is a great start. Here are upgraded options.

1. Box Fan with MERV-13 Filter (Corsi-Rosenthal Box)

When to use: When you need better filtration than a single filter but still want a DIY solution.

Pros: Significantly higher air flow, captures fine particles including smoke and allergens, costs under $50
Cons: Bulky, moderately noisy, filters need replacement every 2-3 months
Difficulty: Easy
Estimated cost: ~$30-50 for box fan plus 4 filters

2. HEPA Air Purifier (Commercial Unit)

When to use: Bedrooms, home offices, or rooms where someone has allergies or asthma.

Pros: True HEPA captures 99.97% of particles 0.3 microns and larger, quiet modes for sleep, auto-mode adjusts to air quality
Cons: Replacement filters cost $20-50 every 6-12 months, electricity use, some produce ozone
Difficulty: Easy (plug in)
Estimated cost: ~$60-200 for the unit plus ongoing filter costs

3. Whole-House HVAC Filter Upgrade

When to use: Homes with forced-air heating/cooling that want whole-house filtration.

Pros: Filters all air passing through the system, no additional appliance, changes with regular HVAC maintenance
Cons: Higher MERV ratings restrict airflow (may stress HVAC), does not help rooms without ducts
Difficulty: Easy
Estimated cost: ~$15-40 per filter, changed every 1-3 months

Tips for Better Indoor Air Quality

A DIY fan-and-filter setup handles particulates, but a few additional habits make a noticeable difference, especially during wildfire season or allergy peaks.

Seal gaps around doors and windows first. The cheapest air purifier in the world cannot keep up if smoky outdoor air is leaking in through weatherstripping gaps. A $5 roll of foam tape around a drafty window does more than running the fan on high.
Match the filter to the fan snugly. Air takes the path of least resistance. If there is a gap between the filter and the fan frame, unfiltered air bypasses the filter entirely. Use painter’s tape or cardboard shims to close any gaps.
Run the fan on medium, not high. A slower fan speed gives air more contact time with the filter media, which actually improves particle capture. High speed moves more air but catches fewer fine particles per pass.
Replace or vacuum the filter when it turns visibly gray. A clogged filter restricts airflow and forces the fan motor to work harder, shortening its life. During heavy smoke events, filters may last only two to three weeks.
Keep interior doors open. Air circulation between rooms lets the fan-and-filter clean a larger volume. If you close every door, the purifier only cleans the single room it sits in.
Add houseplants for supplemental help. Spider plants, pothos, and snake plants absorb some volatile organic compounds. They will not replace a filter, but they contribute and improve humidity.
Avoid adding pollutants indoors. Burning candles, using aerosol sprays, or cooking with high-smoke oils all add particles your DIY purifier has to remove. Ventilate briefly after cooking, then reseal.

Essential Tools and Materials

Building the DIY air purifier shown in the video requires almost nothing beyond what most households already own.

Item	Purpose	Approximate Cost
Box fan (20-inch)	Provides airflow to pull air through the filter	$15-25 (or free if you already own one)
Furnace filter (MERV 11-13)	Captures dust, pollen, smoke particles, and pet dander	$8-20 depending on MERV rating and size
Bungee cords or painter’s tape	Secures the filter flush against the fan intake side	$3-5
Cardboard (scrap)	Fills any gap between the filter edges and the fan frame	Free
Replacement filters (2-3 pack)	Ensures you have spares on hand during extended smoke events	$15-40 for a multi-pack

Upgrade option: For the Corsi-Rosenthal box design, buy four MERV-13 filters and tape them into a cube with the fan on top blowing outward. This multiplies the filter surface area by four and significantly increases clean air delivery rate.

Common Air Purification Mistakes

These errors reduce the effectiveness of even the best DIY air purifier setup.

Placing the fan-filter unit in a corner or against a wall. The fan needs unrestricted airflow on both the intake and exhaust sides. Position it at least 12 inches from walls and furniture so it can circulate air through the entire room.
Using a low-MERV filter to save money. MERV 1-4 filters (the cheapest fiberglass type) catch only large dust particles and do almost nothing for smoke, pollen, or fine particulates. Spend the extra few dollars for MERV 11 or higher.
Running the fan only when you can see or smell smoke. Fine particulate matter (PM2.5) is invisible and odorless at moderate concentrations. If your area has an air quality alert, run the purifier continuously even if the air looks clear inside.
Taping the filter to the wrong side of the fan. The filter should go on the intake side (the back of a box fan, where air is pulled in). Placing it on the exhaust side reduces effectiveness because pressurized air finds gaps more easily than suction does.
Forgetting to check the filter arrow direction. Furnace filters have an arrow indicating airflow direction. The arrow should point toward the fan. Installing the filter backwards reduces particle capture and can cause the filter to collapse against the fan blades.

When to Call a Pro

DIY fan-and-filter purifiers handle most situations, but certain air quality problems go beyond what a box fan can solve.

You suspect mold in the walls or HVAC ducts. Mold spores circulate through ductwork and a room filter cannot address the source. A certified mold remediation specialist should test and treat the affected area before you seal it back up.
Carbon monoxide or gas odors are present. Particulate filters do not remove gases. If your CO detector alarms or you smell natural gas, evacuate immediately and call your utility company or 911.
Your HVAC system is undersized or failing. If upgrading the furnace filter to MERV-13 causes the blower motor to struggle or the system to short-cycle, an HVAC technician needs to evaluate whether the ductwork and blower can handle the increased restriction.
Someone in the household has severe asthma or immune compromise. Medical-grade air quality may require a whole-house HEPA filtration system integrated into the ductwork, which must be professionally designed and installed.
Renovation dust includes lead paint or asbestos. Homes built before 1978 may contain lead paint, and older insulation may contain asbestos. Disturbing these materials without proper containment and HEPA vacuuming is a serious health hazard requiring licensed abatement.

For more ways to maintain healthy living conditions at home, see our home maintenance checklist and seasonal home maintenance guide.

Always verify contractor licensing and insurance in your state. Cost estimates are averages and may vary by location.