Introduction: Cheap Filtered Ventilation

[ currently under editing ]


I will present in the following pages my idea and the implementation of a very cheap and efficient method of obtaining fresh and filtered air from outside.


@ time of creating the English Version, 2020-05-13 19:19, I have just "raw" translated by Google Translate the Original Articleă-Ieftină/ written in Romanian.

So, if some English is un-readable, feel free to blame Google. 😀

This shall be revised as soon as possible.

Step 1: Motivation

We are all concerned about the quality and pollution of the air we breathe.

Due to the industry and gasoline / diesel vehicles, we have more and more dangerous particles in the air. Although I am not an expert in this field, the demonstration shows that PM10, PM2.5 and PM1 particles fly around us and we finally breathe them.

Since we are currently quarantined due to the Corona virus at the time of writing, the numbers look pretty "good".

This is from: and the current date / time is: April 18, 2020 9:54 PM.

At the moment I do not have historical data for a comparison with the conditions when everything goes 100%.

Even without that, another very annoying thing is what happens when you open the windows to ventilate, the wind blows and a lot of dust lands everywhere.

That is, of those 60 tons of dust that fall from the cosmos every day on Earth, 59 tons land in my living room. 😀

How, like all of us, I personally have the same problem at home, I decided to make this very cheap filtered air ventilation.

Step 2: The Idea

Where did this idea come from?

Well, very simple.

To protect computer fans use a very cheap solution, even if it may not be the best.

I simply put in front of the lower intake fan, a filter made of ... Women's Stockings 😀

You can laugh as much as you want!

Then keep reading ...

Figure 1: Attaching a piece of women's sock to the front / down intake fan grille.

Step 3: Front / Bottom Intake Fan Covered by Filter

Picture 2 : Front / bottom intake fan covered by filter.

You can see the light in the "fog" and the soldering tape all around.

Step 4: The Hole...

Good. Suddenly, this idea came to my mind :

What if I drilled a hole in an outside wall and made a filter made of women's socks outside?

Technically, that would be it.

Unfortunately, to ensure a decent airflow, the room must have negative pressure.

Even more, although women's socks are a decent barrier to dust, they are also a barrier to air.

Solution : I simply add on the other side of the wall, so on the inside, that is, a computer fan.

It can be the cheapest, it can be the most efficient and most expensive, as your heart and / or pocket crave.

As you manage to fix the filter on the outside, use your imagination and possibilities, as well as for the fan, inside.

Just be careful not to hurt yourself or others.

My method of implementing the idea follows, considering that I live on a high floor and I have absolutely no access to the outside of the wall.

I simply added a plastic pipe to the project, from those used in sewer systems.

Good! Ready to start trying to have an impressive clean air at home?

It's like I'm selling you something, isn't it? 😀

If the answer is "Yes", then let's go.

I will simply present pictures, not necessarily in perfect chronological order, but as I see fit, so that everyone understands the idea perfectly.

Certainly, this is not a "how is made", but a "how I did it".

Use your imagination and possibilities.

Step 5: The Wall

Image 3 : First, I carefully chose the wall where the hole was to be drilled.

There are many reasons why I chose this wall.

You will definitely find the right one.

Yes, yes, I know, we need a new paint, because we ruined the current paint with another project, as crazy as this one 😀

Step 6: Execute the Hole

Image 4 : Using specific tools and methods, I drilled a hole with a diameter of 130 mm in this beautiful wall.

Step 7: The Hole

Image 5 : Freshly drilled hole.

Due to the thickness of the wall, the length of the hole is about 24 cm.

Do you see the light?

Dust and dirt probably caught your eye first, didn't they? 😀

Step 8: Dirty Game

Image 6 : Drilling the hole in the wall damaged the outside of the wall quite badly, insulated with expanded polyester, fiberglass and plaster.

I don't have pictures of the outside of the hole before repairing it, but it was dust, especially the part on the wall of the building, some material broke there.

As I like to play dirty 😀 I decided to add a few strips of wet cotton handkerchiefs very generously soaked in washable paint and try to spread them very nicely on the edge of the hole and on the outer wall.

The strips did a very good job.

Step 9: Outside the Hole

Image 7 : The outside of the hole, after I repaired it.

If you look closely, although I stretched as hard as I could the strips of wet cotton handkerchiefs generously soaked in washable paint, the mistakes are obvious.

Please note that this was done from the inside, using exactly one dirty hand 😀 with no way to see what I was doing.

It's not that bad, is it?

It was like that joke with the gynecologist who repaired the carburetor through the exhaust pipe ...

Step 10: Plastic Pipe

Image 8 : Plastic Sewer Pipe , 1 meter long, 125 mm in diameter, brand new.

It is not visible that at the bottom it is shaped so that it is able to receive another pipe with a diameter of 125 mm.

This thing helped me a little, as you will see in the following pictures. sn2-dn-125-mm-x-1-m/000000000010801048

Step 11: Cut Pipe

Figure 9 : Cut pipe

You can now see, very well, on the left side the extra diameter, about 130 mm outside diameter, by chance.

Exactly as my hole was 😀

There was another piece of pipe, with a rubber gasket on the inside, also on the left side, which I cut and that ring / collar, larger than 130 mm in diameter, remained.

This was not accidental, I cut it calculated, to be perfectly sure that the pipe will not fall outside the wall, even without fixing, etc.

Step 12: Pipe Outside

Figure 10 : The pipe coming out about 1-2 cm in outside wall .

It may not be the happiest approach, because in winter the snow can gather there, as we have already noticed.

Yes, it snowed a few days later.

Step 13: Pipe Inside

Figure 11 : And the simply perfect fit inside .

See now the effect of the additional 130+ mm ring / collar.

Step 14: Pipe Rings

Figure 12 : From the remaining pipe, I cut several rings to be used to create the filters inside the pipe.

Yes, I made several filters.

Step 15: Matching the Rings

Figure 13 (does not exist): An explanation is required.
It is perfectly clear that a ring with a diameter of 125 mm has absolutely no chance of falling into the same pipe from which it was cut.

Due to this, I cut each ring, then inserted the ring inside the pipe, then carefully measured and cut again to fit the new inner diameter, as close as possible to the inner diameter of the pipe.

The cuts on each ring will be seen in the following pictures.

Step 16: Women's Stockings

Figure 14 : Women's stockings

I simply bought from the store, Women's Stockings 15 DEN on Black.

I wanted a DEN as low as possible, to be as thin as possible and as permissive as possible with the air.

Now, this is exactly how it happened.

The lady at the cashier's office, seeing me buying Women's Stockings and we've known each other for a while, we exchange some jokes, she simply asked me:

"Wow, do you have fantasies with these socks?"

Me: “Yes, ma'am! I want to rob a bank! ” 😀

The lady: “Wow, then these socks are the perfect choice! ”

Step 17: Pulling the Ring Into the Sock

Figure 15 : Take the ring.

You can see the cut of the ring at the bottom.

Make a knot on the stockings.

Make sure it's perfect.

Put the ring inside the trouser leg.

Stretch as much as possible, but carefully, you can break the ring, not the socks.

Carefully make another knot on the other side.


Step 18: Double Sock Air Filter in Women’s Stocking 15 DEN on Black

Image 16 : At the moment you have the owner of a very beautiful Double Air Filter Sock in Women's Stockings 15 DEN on Black 😀

Just keep in mind that you will have to somehow pull the knots, on one side and not in the middle as it is here, soon we will see why, what and how.

Step 19: The Filter in Pipe

Image 17 : Here you see the filter, perfectly fit in the pipe.

Where are the knots?

You can see them in the image below.

Step 20: Interior View of the Pipe

Figure 18 : Interior view of the pipe .

Now you can see the nodes.

This is what I said above, with the knots pull on one side of the filter.

Step 21: Filter Outside

Image 19 : And then I just wanted to see what my women's stocking filter looks like again.

And let me grow up! 😀

Step 22: Other Filters

Image 20 : I made other filters .

On the left is a Sock Filter with a Hole on one side .

In the middle is the Activated Carbon Filter , simply glued to one side of the ring.

On the right is the Himalayan Salt Filter , during construction, the most complicated by far.

None of these are necessary, I just like to play. 😀

Keep in mind that the more filters you add, the harder it will be for them to pass through and you will eventually have an inefficient air filter.

Simply do them if you think they will add value to the quality of the filtered air.

Step 23: Activated Carbon Filter

Figure 21 : Activated Carbon Filter

It is said to be able to remove odors.

Definitely one wants to install it after the dust filter.

Eventually, keep it only as a dust filter.

However, it has a high resistance to air flow, I gave it up in the end.

Step 24: Stocking and Activated Carbon Filters

Figure 22 : Stocking and Activated Carbon filters , illuminated below.

The more light is stopped, the more it will be with the air too.

Step 25: Himalayan Salt Filter

Image 23 : Himalayan Salt Filter

Himalayan salt is certainly not mandatory, any salt is welcome.

I wanted this because it’s Pink. 😀

I wanted a salt filter, because the benefits of Salt Aerosols are well known.

Do your own research if you want to find out more.

What can you see here?

We have prepared two "lids", made of fiberglass which is used in construction.

This is what I had, it has holes about 5 mm (Insect net should be very good, 2-3 mm), which are larger than a grain of salt.

So I had to engineer something. From a complete packet of salt I was able to sift some of the largest grains of salt, as can be seen.

See how cute and pink they are on the left.

The rest, I sifted even more, to have the smallest dimensions, about 1-2 mm in diameter.

Then I put glue on both sides of the fiberglass and hoped that as many salt grains as possible would stick together.

I was not 100% successful, as you can see in the picture.

At the end, I glued both covers to the ring.

Larger salt granules were left inside the filter.

Step 26: Commercial Salt Filter

I "thought" that something similar to my idea must be available on the market to prove my theory.

I searched and found this (image on the left):

Step 27: Himalayan Salt Filter

Figure 24 : At the end, the Himalayan Salt Filter looks like this.

Yes, a few grains of salt will still fall, absolutely no problem.

We put them at Tocăniță ( some Romanian food ), now with the taste of Glue! 😀

Step 28: Himalayan Salt Filter in the Pipe

Figure 25 : Then carefully install the Himalayan Salt Filter in the pipe.

Certainly, in the airflow, we want this Filter to be the last.

Step 29: Computer Fan

Figure 26 : Computer fan and the secret of why I did not repair the inside of the hole and the inside wall around it.

I played with several computer fans, from the cheapest and noisiest, 12 cm in diameter, others 2 x 14 cm in diameter.

I was not at all satisfied with the air flow and in the end I decided to buy it, 12 cm in diameter, 100 cubic meters of air / hour, noise 18 dB, 150 thousand operating hours, ie until the End of the World. 😀

Quite expensive, almost top in its class, but practically no noise.

Now, don’t imagine that about a hundred cubic meters of air / hour fly through my living room and I hold my hands and feet on furniture and other handles.

Definitely not, the airflow is partially blocked by filters.

And, as you can see from the picture, as it is mounted, for tests, it looks impressively ugly and not professional at all.

This is the reason why, from the beginning of the project, we decided that the Fan will be tubed in the Pipe, as follows.

Step 30: Cutting the Fan

Figure 27 : The most complicated part is carefully measuring where we will cut.

Of course, if you cut too much, you can use something, insulating tape to compensate, etc.

Or, we can do it perfectly! 😀

Step 31: Partial Fan in Pipe

Figure 28 : After a few hours of work, I partially inserted part of the fan inside the pipe.

Step 32: Tubed Fan

Figure 29 : But in the end, I did it.

The most complicated and difficult cuts I have ever measured and cut.

Especially since I didn't have a fan yet if I broke this one.

You may notice that the fan has been pushed into the pipe until it can no longer move, due to the decrease in pipe diameter.

Bonus : a cool repair of the inner wall.

I'm not good at any of this 😀

It will be repaired one day.

At this point, you can open a Beer. You deserve it! 😀

In the meantime, let's take a deep breath of some Clean and Salty Mountain Air ! 😀


Final Status in the order of entry of air from outside to inside, so: Double Socks Filter, Himalayan Salt Filter and obviously Tubed Fan.

The Pipe is perfectly removable, non-stick, non-screwed, nothing.

Step 33: That Would Be All, Folks!

That would be all, folks!

What else can I write here?

You saw the ideas, the methods, the tools, you saw step by step what and how I did.

Definitely, you have the freedom to implement it as you can and with what you have at hand.

Step 34: A Pseudo - Questions and Answers Section

Q : How is it feeling ?

A : I could certainly exaggerate, but I feel it as I would in a Forest. The air is like that, very clean.


Q : Have you ever opened your windows to ventilate ?

A : Absolutely not, for a few weeks now. Yes, I opened the windows for some reason, but not to ventilate the air.


Q : Do you feel like you are breathing salty air ?

A : Certainly not, there is very little salt in the filter, as seen, however my opinion is that even very little is infinitely more than nothing. I am very happy that the air that enters the house comes in contact with all those (caresses) grains of salt. If you want to feel the effect, very amplified, open a bag of salt and take a deep breath of air from the bag.


Q : Bad things ?
A : Yes, the constant inflow of air creates a flow of air through the house, which can be annoying / annoying for some people. However, although I have not said anything about it, the fan is powered from a power source that has several voltage levels: 12, 9, 7.5, 6, 5, 4.5 and 3 Volts.

Computer fans usually operate at lower voltages than the rated voltage.

I supply 12 V fans at 5 volts, with absolutely no problems.

The lower the voltage, the lower the speed / RPMs, but also the lower the air flow.

Also, with a very simple automation, you can install an electronic stopwatch or a light sensor to power the fan at certain intervals or during the day.


Q : Other bad things ?

A : Yes, the air is colder overnight, so for some people it may not be as good. Some would like to heat it.


Q : How much did it cost ?
A : Hmm, let me remember. Drilling the hole: 200 RON. Pipe: 16 RON. Women's socks: 9.95 RON. Computer Fan : 77.99 RON. Power Supply : about 40 RON, I already had it. Adhesive, wet cotton handkerchiefs, salt, washable paint, they are quite cheap, I had them around. [ Currently @ 2020-05-13, 1 RON is $0.22 USD ]


Q : How long have you been working on this?

A : Since I played a lot, testing different things, I can appreciate that it lasted about 20-30 hours.


Q : You talked about Filters, Stocking Filters, Single and Double, Activated Carbon Filter and Himalayan Salt Filter. What did you keep in the end?

A : Now I realize that from all my play, this may not be the case.

Finally, they remained in the Pipe, in the order of air entry, from outside to inside, as follows: Double Sock Filter, Himalayan Salt Filter and obviously, the Tubed Fan, which look I did not write anywhere, is installed with the meaning to draw air from outside.


Q : You talked about the hole and the damage , the costs and the work . It's not a lot of effort for a trivial Filter with ... Socks?
A : I am the kind of person who if an idea comes to his mind, and it seems to me that the idea makes some sense and can bring benefits and involve reasonable costs, as you saw above, I try it and see what comes out.Now, about the Women's Stockings filter. There are commercially all kinds of filters and you can put any kind of filter. The solution with Women's Socks seemed to me extremely simple, practical, decent in efficiency and almost cost free.


Q : Why didn't you buy something like that? A ready-made solution ?

A : I searched the Internet for something like that, but I couldn't find it.

Basically, I am not aware of such an "Outside Air Filter".

Later Edit @ 2020-05-13 In the meantime I have learned about this :

and this :

and this :


Q : Why didn't you buy an Air Purifier, like ?
A : Well, there are two fundamentally different things. An Air Purifier purifies the air that already exists in a room. My solution brings fresh air from outside, filtered by dust, possibly filtered with Activated Carbon and Salt. Look, if it were an Air Purifier, with the possibility of being able to take in air from outside, it would be a very good job.

Q : What can you tell us about Maintenance : how long do you change / wash the Filters?

A : There is a trick and this is where the "Very Fine Things" begin.

- 1st, the Sock Filter is exposed to the Environment, and therefore the Rain, which "washes" it.

- 2nd, any Dust Filter, somehow becomes more and more efficient in gathering smaller and smaller particles, as it gets clogged, although at the same time it loses its initial ability to filter what it filters, in our case the air, becoming more and more blocked.

- If someone wants, disassemble it, make a shower to the Sock Filter, let it dry, and put it back in the Pipe. Then mount the Pipe back in the Wall. Bonus: A Bier ! 😀

- To be changed , at most the material from which the Women's Stockings are made is Polyester and technically it should be destroyed in the end by the Ultraviolet Radiation from the Sun. Let's say once every 6 months - 1 year. It costs a few centimeters of Women's Stocking, I said 0.2 RON. I think we can consider it "maintenance free".

Q : What about operating costs? How much does the electricity cost?

A : Well, let's do a little calculation, taking as a reference the fan we mounted.

This one, NF-S12B Premium Fan, consumes 0.9 Watts @ 12 Volts.

Let's say 1.0 watts to cover the losses of the Power Supply.

This means: 1.0 Watts / hour. Currently in Romania, 1 kWh costs 0.65 RON, when I did the last calculations, including Taxes, Excises, Green Vouchers, etc.

This means that 1000 hours of continuous operation costs 0.65 RON.

Or, in other words, it costs you 0.0156 RON / day, 0.1092 RON / week, 0.468 RON / month (30 days), respectively 5.694 RON / year. I think we can consider that it works "for free".

Step 35: Addendum

Any other interesting pictures I took during the tests are also here, I told you that I really like to play.

And a few other ideas as well.

Step 36: First Pipe

Figure 30 : The first pipe I experienced, as I had it, 110 mm in diameter.

Step 37: Very Simple Filter

Figure 31 : A very simple filter.

Simply pull the women's socks over the pipe and fasten them with what you have at hand, I used transparent tape.

Step 38: Filter With Women’s Stockings 15 DEN on Black

Image 32 : A very new Filter with 15 DEN Women's Stockings on Black 😀

However, quite bad, because the filter is not uniform at the entrance to the hole.

For a test, however, it is absolutely irrelevant.

Step 39: First Version

Figure 33 : The first version, for testing purposes, of the women's stockings filter, 110 mm pipe and the cheapest computer fan I had around, the cheapest and noisiest fan I had.😀

The computer fan is 12 V, about 12 RON Price.

Pretty noisy. High airflow.

A very good start.

If we under-power the computer fan, the noise is greatly reduced, but also the air flow.

You can see the stockings on the other side of the pipe, as seen in the picture above.

Step 40: Dust I Didn't Breathe in Exactly One Week

Image 34 : Et, voilà!

The dust I didn't breathe in exactly one week.

It was somewhere in the early quarantine, after mid-March, 2020.

Step 41: 140 Mm Computer Fan on Red

Image 35 : Computer Fan, 140 mm, 900 rpm.

The airflow is quite low, but quite quiet, the noise is only 18 dB.

If you look closely, notice the transparent tape around the fan to cover all the tiny spaces where false air could be absorbed.

Do you like Red too? 😀

Step 42: Adhesive Tape

Figure 36 : As I decided to test with a single layer of stockings, I added a few rounds of transparent tape, then I burned one side of the stockings.

Step 43: One Layered / Sided Filter

Image 37 : Empty part of the filter, now Single Stockings.

Pretty ugly.

I just burned the Women's Stockings 😀

This filter is what currently filters the air entering the house.

[ Meanwhile, after 2 weeks from the initial date of writing this document, I returned to the Double Stockings Filter ]

Step 44: Dusty Filter

Figure 38 : Dusty filter after several days.

Remember that almost nothing moves around, because it is quarantined and you have seen the numbers from the air testers at the beginning of the document.

You can see in the lower left the HEPA filter of the vacuum cleaner that I have in the house and which simply gave me another idea.

Step 45: HEPA Filter

Image 39 : A HEPA Filter for Philips Vacuum Cleaner, like this:

They say it's HEPA 12, so it will store / filter up to 0.3 mm particles, which is 99.95% of the dust.

They say, not me!

The dimensions fit decently with our pipe.

Is this giving you some ideas ?

Step 46: UV Lamp

Figure 40 : Adding a small UV Lamp inside the pipe can help the air to be even cleaner of unwanted pathogens, for example Corona Virus.

The lamp in the image is provided for reference / example only.

Step 47: Thank You!

Finally, I hope you enjoyed this original idea and project of mine and have some ideas to play with and improve your life and health!

Thank you very much for your attention!

Thanks to the reviewers, who helped me correct the mistakes and explain things I missed!

Enjoy! Be healthy! Stay safe! Stay home! Go Romania!

Lupulainen @ Romania

Monday, April 20, 2020

(Last modified: Saturday, May 2, 2020)


"Raw" English Version : Wednesday, May 13, 2020.

[ Currently the English Version has never been reviewed, to be done. ]