DIY Box Fan Air Filter: Build Guide

Why Four Filters Work Better

One filter surface (400 sq inches) versus four filter surfaces (1,600 sq inches).

More surface area means less resistance, longer filter life, and more total air cleaned per hour.

Why the Lasko Fan?

The Lasko 20" box fan dimensions match standard 20x20 filters perfectly. The edges seal together cleanly.

Important: Save the cardboard box when you unpack the fan. You'll use it to seal the bottom of your filter box.

Step 1: Check Filter Arrows

Every filter has an arrow printed on the cardboard frame. This shows airflow direction.

All four arrows point inward toward the center where the fan will sit.

Step 2: Build the Filter Box

Stand the four filters on their edges to form a square box. Arrows point inward.

Tape the vertical seams where filter edges meet. Seal completely from top to bottom. No gaps.

Step 3: Seal the Bottom

Cut a flat piece from the Lasko cardboard box slightly larger than the filter box opening.

Tape this cardboard to the bottom edges of all four filters. Creates a sealed box with filter surfaces as the only air entry points.

Step 4: Attach the Fan

Place the Lasko fan flat on top of the filter box opening.

Tape around all four sides where the fan frame meets the filters. Seal completely so air cannot bypass the filters.

Step 5: Run It

Plug in and turn on. Air pulls through all four filter surfaces before the fan pushes it back into the room.

Replace filters when visibly dirty or airflow weakens. Typically 3-6 months.

What This Filters

• Dust and dust mites
• Pollen and pet dander
• Mold spores
• Smoke particles
• Bacteria and viruses (with MERV 13)

Does not filter:

• Odors (needs activated carbon)
• Does not add fresh outdoor air (recirculates only)

This supplements your home's ventilation and filtration. It does not replace it.