How to Make an Air Filter

High-end air filters get pretty costly, but you don’t have to let a price tag get between you and cleaner air. If you have some basic supplies or construction skills, you can make your own filter for a fraction of the cost. The easiest way to do this is by simply attaching a filter to a standard box fan. For a more intricate, portable filter, try creating a frame out of a plastic bucket. If you’re good at crafting, use plywood to create a wood frame for a more powerful filter. Install your finished filter in an enclosed room to purify the air and breathe easier at home.

EditSteps

EditRepurposing a Box Fan

1. Purchase a fan you can fit with a filter. Ideally, find a fan that is the same size as commonly available filters. Try using a box fan, since you are likely to find something that fits exactly over it. If you choose something other than a box fan, make sure it has a place you can stick the filter to secure it in place.^[1]
   
   • For example, some round fans have metal spikes in the center where the front cover attaches. You can stick the filter on the spike. It isn’t the prettiest solution, but it’s effective for making a basic air filter.
2. Select a high-quality filter that fits over your fan. Filters are rated for their effectiveness at capturing particles in the air. Look for HEPA filters, which trap even the smallest particles in the air. HEPA furnace filters rated MERV 13 and FPR 10 are the best options available if you can’t get a standard air filter.^[2]
   
   • Filters are available online and at most hardware stores.
   • MERV and FPR are merely rating systems used in different places, so don’t worry too much about them. MERV 13 and FPR 10 indicate the most effective filters used in home settings.
   • You can use alternative filters, such as MERV 11. Lower-rated filters are a little less effective at purifying the air, but they are still good and may save you a little money.
3. Line up the filter so the fan moves air through it. Look for an arrow printed on the filter's frame showing you which way you need to align the filter in order for it to work. You can install the filter in front of or behind the fan, but usually, putting it on the back of the fan is easier. The filter works either way, so it depends on your preference and where you have space to attach it.^[3]
   
   • The arrow always needs to point in the direction of the air flow. When the filter is behind the fan, the arrow points toward the fan’s blades. When it’s in front of the fan, it points away from the blades.
4. Tape the filter in place or use an alternative attachment. The easiest way to keep the filter in position is to use duct tape or another strong adhesive. Simply lay tape over the filter’s frame and the fan’s frame. If you’re not using a box fan, look for alternative attachment points.^[4]
   
   • For example, if you’re using a round fan, remove the front cover and look for a metal spike to skewer the filter on.
   • An alternative attachment method is to use brackets. Drill a pair of holes through the top of the fan’s casing. Purchase brackets with screw openings, screw them to the fan case, then slide the filter underneath the bracket prongs.
5. Put the filter in an enclosed room and turn it on. Small fan filters work most efficiently in smaller rooms, such as bedrooms. Plug the fan in and turn it on to begin filtering. Make sure you feel the fan pulling or pushing air through the filler screen.^[5]
   
   • The filter eventually stops working, so plan on removing it when it starts turning black. Replace the filter about every 90 days.

EditUsing a Plastic Bucket

1. Measure the diameter of a small fan. The fan needs to fit inside whatever plastic bucket you plan on using for the filter. Try using a bucket for maximum space and filtration. Choose a fan, such as a portable fan designed to sit atop a table, that fits in the bucket. After figuring out its diameter, subtract about from the final measurement.^[6]
   
   • Subtracting a little length from the diameter ensures the fan doesn’t fall through the lid when you install it.
   • Another option is to put the fan inside a small laundry basket. Laundry baskets usually have air vents, so you don’t need to cut out holes like you do with a bucket.
2. Cut a hole for the fan in the bucket’s lid. Mark the lid with a pencil, creating a hole in the center according to your diameter measurement. Use a utility knife to cut out the plastic you need to remove. Work carefully to avoid damaging the outer edges of the lid.^[7]
   
   • Remember to make the hole a little smaller than the diameter of the fan. Center the hole and keep it as even as possible all the way around.
3. Make holes in the bucket to let air into it. Creating the holes can be somewhat time-consuming, but a hole saw cuts right through the plastic. Try using a -diameter blade to drill cleanly through the sides of the bucket. Create the holes in columns, leaving about of space between each hole.^[8]
   
   • You can make about 5 holes per column. Make as many columns as possible to let plenty of air into the bucket for filtering.
   • Try making some of the holes a different size. Drill 4 columns on opposing sides, then switch to a drill bit. Fill in the remaining space with columns of bigger holes.
   • Consider sanding the holes smooth with 120-grit sandpaper or a rotary tool to improve your filter’s appearance.
4. Choose and cut a filter to fit into the bucket. Shop for a HEPA filter, preferably one without a frame. Once you have the filter, measure the bucket from the bottom to just above the top hole. Measure this same width on the filter, then cut it to size with scissors.^[9]
   
   • If your filter has a frame on it, cut around the frame first to remove it. Another option is to install the filter on the side of the bucket by drilling one big hole instead of a bunch of small ones.
5. Roll the filter up and fit it in the bucket. Use the filter as a liner inside the bucket. Push it against the sides of the bucket until it sticks in place, covering the holes completely. The filter usually sticks in place if it is the right size, but you can also add duct tape to secure it to the plastic.^[10]
   
   • Rolling the filter up a few times can help you fit it. Most filters are square-shaped, so they tend to curl up and fall over until you break them in.
6. Cut a notch in the top edge of the bucket for the fan cord. Use a crafting knife or another tool, such as wire cutters, to make the notch. Make it about in size. Test the notch by attempting to slide part of the fan’s electrical cord into it.^[11]
   
   • Make sure the cord stays firmly in the notch, out of the way of the lid.
7. Fit the fan inside the lid and the bucket. Slide the fan through the lid so the fan’s blades face upward. The top half of the fan’s case sits on top of the bucket so the fan blades blow air back into the room. Drop the base of the fan down into the bucket, leaving the cord in the notch you cut. When you're done, plug the fan into the nearest wall outlet to begin purifying the air in the room.^[12]
   
   • Remember to check the filter every so often. It gets dirty as it takes in debris from the air, so replace it about every 3 months.

EditBuilding a Wood Frame

1. Take the back casing off of a box fan. Select a fan you wish to use for your filter. The ideal fan is a box fan since similarly-sized filters are common. Locate the screws on the back part of the fan and turn them counterclockwise to remove half the case, as well as the fan’s handle if it has one. Leave the other half of the case in place over the fan blades.^[13]
   
   • You can remove the fan’s control knob if you wish by locating a screw close to it on the frame. Replace the knob later with a longer one made from wood attached to a bronze pipe.
   • As an alternative, also remove the front part of the case. After measuring the fan’s diameter, cut a matching hole in a piece of styrofoam. Divide the styrofoam into 2 halves to fit around the fan, preventing the filter from rattling while it is running.
2. Measure and cut plywood boards for the filter’s frame. To create an inexpensive but durable frame, get several -thick pieces of plywood. Cut 4 boards to be a little longer than the fan. If you're using a standard box fan, make the boards about in size.^[14]
   
   • If you’re using something other than a box fan, measure the fan as needed to determine what size its frame needs to be. The frame always needs to be bigger than the fan so you can install the filters behind it.
3. Mark slots for the filters in one of the frame boards. Measure up about from one of the longer edges on the board. Mark the spot, then measure another . The first filter fits in the area between these marks, so repeat the measurements again to fit the second filter right behind it.^[15]
   
   • Use a ruler to make straight lines all the way across the boards through the areas you marked. Leave the outlines about short of the sides of the board.
   • You may wish to mark the slots with diagonal lines or other pencil marks to ensure you don’t cut the wrong areas. The areas you need to cut can be a little tricky to distinguish.
4. Cut the slots into the board with a jigsaw. Use the jigsaw to cut out the parts designated for the filter slots. The slots don’t extend all the way to the edges of the board, so be careful when cutting. Leave a small perimeter of wood around each slot, as indicated by your outline, to ensure the frame is steady.^[16]
   
   • Wear goggles, ear muffs, and a dust mask to protect yourself while you work.
   • If you don’t have a jigsaw, try using a table saw or circular saw. Lower the plywood onto the saw carefully, cutting along the outline you marked on the wood.
5. Use wood glue to bind the pieces together. Arrange the boards in a box shape, positioning the board with the filter slots on the left or right. Then, spread glue between the board joints, pressing them together until they stick in place. The glue takes about 30 minutes to begin solidifying, but for maximum effect, wait about 24 hours for it to cure.^[17]
   
   • Use clamps to hold the frame together while assembling it and waiting for the glue to dry. You can also take this opportunity to add nails to secure the boards together more firmly.
   • Test the frame by fitting the fan in it. Place the fan on the opposite side of the slots for the filters. Align its edges with the edges of the boards.
6. Cut 3 wood strips to form tracks for the filters. Create pieces about in size by cutting the remaining plywood or by using other wood scraps available. Reduce the length of each strip as needed so you are able to barely squeeze it inside the frame.^[18]
   
   • Test the parts as needed by attempting to place them inside the frame. Cut them down gradually until you are able to fit them securely.
7. Glue the track pieces to the bottom part of the frame. Line the wood pieces up with the slots you cut in the side of the frame. Place one of the pieces right behind the fan, gluing it to the bottom frame board with wood glue. Leave a gap between it and the second piece. Repeat the pattern with the third piece.^[19]
   
   • Make sure the wood pieces line up properly with the slots. If they block the slots, you won’t be able to slide the filters into place.
8. Cut and glue a plywood border over the top of the fan. The border neatens up the filter and helps hold the fan in place. First, measure the distance between the fan’s casing. Outline this in pencil on a piece of plywood, cutting it out with a jigsaw or another tool. When you’re done, glue it to the frame boards around the fan.^[20]
   
   • Put the border on the front side of the filter, but make sure it doesn’t cover the fan’s blades.
9. Slide the filters into the slots to complete the filter. Purchase some quality HEPA filters for your device. Get square filters the same size of your fan, usually . Simply push them into the frame by using the slots you cut on the side. When you need to remove them, pull them back out of the slots.^[21]
   
   • Look for the arrows printed on the filters. Make sure they point in the direction of the airflow, which means the arrows point toward the fan blades in this design.
   • This is a basic, strong filter, but you can customize your design. For example, make the frame bigger so you can put an extra filter in front. Try creating a handle or cutting a slot for the power cord.

EditTips

• Store-bought air filters are expensive, but they contain the same kind of technology you use in homemade ones. The homemade ones are just as effective despite being much cheaper.
• Customize your filter design. All filters operate the same way, but you can use different techniques or materials to make components like the frame.
• Filters need to be changed out every so often. On average, quality filters last 3 months, but you may need to change yours more frequently due to pets or other factors.

EditWarnings

• Using saws and other cutting tools is dangerous, so always take proper safety precautions. Wear protective goggles, ear muffs, and a dust mask.

EditThings You’ll Need

EditRepurposing a Box Fan

• box fan
• HEPA filter
• Duct tape

EditUsing a Plastic Bucket

• Desktop fan
• bucket
• Utility knife
• Pencil
• Hole saw
• saw blade
• HEPA filter

EditBuilding a Wood Frame

• box fan
• 2 HEPA filters
• 4 or 5 -thick pieces of plywood
• plywood strips or scraps
• Ruler
• Pencil
• Straightedge
• Jigsaw or table saw
• Wood glue

EditReferences

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