Introduction: Simple and Cheap Homemade Air Filter

Picture of Simple and Cheap Homemade Air Filter

This is a guide for your average DIYer that wants a cheap and easy solution to improve the indoor air quality of his/her medium to small sized living space. By forcing air through activated carbon, you can effectively “scrub” the air of organic particles and other pollutants like dust. This scrubbing ability is due to the carbon's ridiculously large surface area to volume ratio. The surface area of one gram of carbon can be anywhere from 500 to 1500 m2. At 500 m2 per gram, about ten grams of activated carbon would have the surface area of a football field (only about 3 and a third grams at 1500m2/gram)! How can this even be possible one might ask? A property of activated carbon known as microporosity is responsible for this phenomenon. Tons of tiny holes are present in each granule of carbon for pollutants to filter through. Because activated carbon isn’t very reactive, it is non-toxic and safe to handle. This relatively cheap material can be used as an effective DIY filtration medium.

Step 1: Materials Needed

Picture of Materials Needed

To begin, you must first gather all of the necessary materials with the first two being the most important:

· A Fan

· Activated Carbon(Can be purchased online or at a local pet store)

· Window Screen

· Cardboard

· Duct Tape

· Stapler/Staple gun

· Knife or scissors

· String, shoelace, aux cord etc. (anything that’s malleable enough to be wrapped around the fan to measure its circumference)

· Measuring tape or ruler

In this design, the fan pulls the air through the carbon filter. That being said, MAKE SURE that your fan is pointed outwards(away from the body of the filter). These instructions will cover a cheap and easy design but can be easily adapted to a more complex/durable one. As long as you have a GOOD SEAL on your fan and filter, the same concepts will apply.

Step 2: Making the Body of the Filter

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First, wash the carbon off using some sort of strainer or screen. You can use window screen inside of a colander if needed. Usually, some fine dust has been knocked off of the carbon during shipping and moving around.

Then, lay the carbon out to dry by spreading it out as much as possible over a flat surface (on top of plastic or something similar so that it can be easily collected later).

Procedure

1) Measure the circumference of your fan. This can be done by taking your string (etc.) and wrapping it around the thickest part of the fan. Once you have fully wrapped the string around the fan, mark the length of the string that you used so that this length can be measured. Now, use your ruler or tape measurer to determine the length of the string (the circumference of the fan).

2) Knowing the circumference, you can begin to measure out the piece of cardboard needed to fit over your fan. We will be drawing out a rectangle on the cardboard. Said rectangle will have a length equal to the circumference of the fan(with a little extra for overlap) and a width equal to the desired length of the cardboard tube. On your piece of cardboard, draw out a line equal to the circumference of the fan PLUS .25 inches. (The extra quarter inch allows for overlap so that you can create a cylinder from this cardboard.)

3) To determine the width of tubing that you should use measure the depth of the fan and multiply this number by three.

4) Cut out this rectangular piece of cardboard and roll it along the grain (corrugation) until the material becomes malleable enough to form a cylinder.

Step 3: Closing Up the Body of the Filter

5) Wrap your rolled piece of cardboard around the fan as shown in the video and staple the top part shut(you are trying to form a cylinder). Now, remove the cardboard from the fan and staple up the other end of the tube. Stapling this end will form the cylinder that we need.

6) Before securing the cylinder to the fan, bear in mind that you will need a way to feed the power cord of the fan from the inside of the cylinder to the outside. One way to get the plug outside is by cutting a hole in the side of the tube just large enough to sneak the plug out. Once the plug is sticking out of the side of the tube, seal the hole around the wire with duct tape.

7) Attach the cylinder to the fan with duct tape.

IMPORTANT: Make sure that you have a very tight seal. A good seal ensures that all of the air being pulled by the fan is passing through the carbon.

Step 4: Creating the Filter Itself

Picture of Creating the Filter Itself

1) Measure the inner diameter of your cardboard tube attached to the fan

2) Calculate the circumference of the inside of the tube by multiplying the inner diameter by pi (3.1416)

3) The circumference plus a quarter inch for overlap is going to be the length of a second piece of cardboard that we will be cutting out. The width will be 1 inch. Cut out this rectangle and wrap it in duct tape to increase its sturdiness. Form it into another cylinder (this cylinder will be only an inch tall so it’ll be like more of a disc) by stapling the top corner of each side together. Next, staple the bottom corner of each side together.

4) Make sure that your screen has a fine enough mesh for the carbon to stay in. If not, it’s ok to double or triple up the screen in order to reduce the mesh size.

5) Take your screening material and begin to staple it around the edge of one side of the disc (Almost like you’re stretching leather over a drum). You want the screen to be as taut as possible.Take your time stretching the screen over the cardboard to ensure that you have a tight fit.

Step 5: Finalizing the Filter

Picture of Finalizing the Filter

6) Once you have fully gotten this part stapled, turn the filter over and begin to secure the screening to the other side. DO NOT seal this side completely; be sure to leave enough of a gap to pour the carbon into the filter.

7) Make sure the carbon is dry. Proceed to the next step once your carbon has fully dried.

8) Make a funnel out of paper and pour the carbon into the top of the filter.

IMPORTANT:Pack your filter to the brim with carbon. Doing so will allow you to lay your filter on it's side(otherwise, the carbon will settle over time and your filter will lose efficiency).

9) Close up the last part of the screen on the remaining side and trim off any excess screening material.

Step 6: Getting Your Filter Up and Running

Picture of Getting Your Filter Up and Running

Now that you have built both components to the filter, they are ready to be combined and your project is almost complete. Before inserting the filter into the body attached to the fan, be sure that the switch on the back of the fan is set to the on position.(Your filter can be turned on and off by plugging it in/unplugging it or by attaching it to a surge protector and using that as a switch.) The filter can now be inserted into the cardboard tube and taped around the edges to ensure the perfect seal. Congratulations! You have now made yourself a cheap and easy air filter. The carbon should be replaced every six months to a year depending on usage and indoor air quality.

Comments

ohitstheronbueno (author)2017-07-30

how to make this applicable to a car exhaust?

ThomasK19 (author)2016-03-22

Hmm. How much air flow can you expect from a device of that size? I have a air/heat exchange in my house (about 200 m2). The filters for in- and outgoing air have approx. 20x20 cm2 with a depth of 5 cm where the paper is folded (so you get at a guess 20x100 cm2 of filter. I don't know the size of the ventilators (it's all in a housing the size of a large fridge) but guess they are decent.

kiserwr (author)ThomasK192016-03-22

Well the fan has a diameter of 4 inches(10.16 cm) so a cross sectional area of pi/4*10.16 cm^2 which is 81.07cm^2 so to find the volumetric flow rate you multiply this number by the velocity of the air which is unknown but you could ballpark it or estimate it using bernoullis equation (http://hyperphysics.phy-astr.gsu.edu/hbase/pber.html). All and all this particular fan doesn't pull air through too rapidly but will circulate air throughout a small/mediums sized room or car over time.This design could also applied to a more powerful fan with more durable materials if one desired to do so

ThomasK19 (author)kiserwr2016-03-22

The main issue is your filter. It has only 2*Pi*5 ~ 30 cm2. This is less than 1/66 of the one in my home system. So when the 2.000 cm2 from my filter are for 200 m2 of room, your 30 cm2 would be enough for 3 m2. So a car or mobile home would be okay. But even a bath room would be to big for your system.

kiserwr (author)ThomasK192016-03-22

Consider the filtration medium. Activated carbon has a ridiculously large surface area to volume ratio and while yes this system clearly cannot replace a home system it can undoubtedly effectively filter the air in a bathroom. This design was made on a small scale but could easily be scaled up by using a larger fan. You could build something to contain the carbon and attach it to the back of a box fan if you really wanted to.

kiserwr (author)kiserwr2016-03-22

Also this particular filter has a larger surface area than that considering that its about the same size of the fan

wold630 (author)2016-03-21

Nicely done! Thank you for sharing and welcome! Can't wait to see what you make next!

MickiV (author)wold6302016-03-21

How clever and practical. And money saving! Good work.

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