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We live in a small single room apartment just under the roof in a city center. Many of our neighbors burn wood and coal (among other things: it often smells of burned plastic). The toxic smoke comes out of their chimneys just a few meters away from our windows (one of them from a shorter building is right under our windows). This lasts all day/night during 6 months per year (*).

We need fresh air for ourselves and also to dry our laundry but when we open the windows our PM sensor goes crazy and the amount of carcinogenic VOC is super high. We can't simply open the windows and then filter the air inside because the air is too polluted (it burns the eyes and leave a burning smell on everything ― the PM are just a part of the problem). We need to find a way to renew our air with clean air directly.

This would be relatively easy if we had two air ducts somewhere in the wall, like a bathroom extractor fans and a kitchen air duct. We would simply use a "sucking fan" (eg. by reversing the bathroom extractor) to suck in the air through an HEPA and a carbon filter and blow it out with a second fan through the second air duct. But there are no such air ducts and our tenant does not allow us to make them.

The only opening we have is a window. So, we need to find a way to suck in and filter the outside air from this window and to reject the indoor air from this same window.

There are several problems to solve to make this system work:

  1. The frame must be both easily removable and hermetic.
  • removable: so we can easily remove it and just open our window when the air outside is clean.
  • hermetic: so that when we use it, all the polluted air from outside passes through the filtration system without leaking from the joints. It should be tightly sealed on the wall, but also around the fan. We should be able to open/close the windows through the frame so that the outside air never comes in (except through the filtration system).
  1. The filtration system should be powerful enough to filter a high debit of air in a single pass. The filtration system should be able to remove the PMs and stop the toxic gaz in just one pass.

What we tried:

We tried to build a removable hermetic frame that we could fix on the wall around the window with an input fan and an output fan. The frame is made of plastic corners (L-shaped) covered with a plastic sheet. We made 3 holes in this plastic sheet:

  • We "filled" the first hole (cf. 1 on the picture), with 4 fans in order to suck in the air from outside through a filtration system, made of an HEPA filter and a carbon filter)
  • We filled the second hole (cf. 2), with a fan that pushes outside the air from inside: this fan pushes the air through a flexible exhaust hose (a dryer vent) of 2-3 meters, to avoid sucking in back the air we just ejected. We added a closed tube/sleeve (cf. 3) to easily throw the exhaust hose outside without having to open the windows before fixing the frame.
  • The third hole (cf. 5) is connected to a closed tube/sleeve we used to open and close the windows and throw/pull the exhaust hose without having to dismantle the frame (we can't open the windows completely because the frame blocks it, but it's enough). We sealed everything wil silicone caulk and added a foam insulation tape on the frame to make a good seal between the frame and the window.

We used butterfly screws (cf. 4) to fix the frame on the window frame (into which we drilled small holes to insert Brass inserts) so that it can easily be removed.

It didn't work: the smell was awful inside (and the PM sensor went crazy)

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The carbon filter we used:
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Several idea to improve it:

  1. improving the filtration system:
  • to filter the PM: we used a, HEPA filter, but they are thick and thus have a high resistance to airflow so it might not be recommended for this.
  • to filter the toxic gas: we used a standard active carbon but we don't know if it's enough for the debit of air passing through (it should clean the air in one pass, as it goes).
  • we are not sure the (4 computers) fans were powerful enough to suck through both filter
  • Concerning the output fan: we are not sure it was enough to block the PM and the gas from outside. We suspect most of the gaz and PM that got into our apartment, were coming through the exhaust fan (even if it was running at the highest speed), as it can happen with water: particule could move upstream)

So how to improve this system? (A completely new design is also welcome)

(*) It's a very common problem in our country. We know from (a long experience) that talking to the neighbors, moving to another place, counting on the law enforcement, or trying to involve the government institutions that are supposed to solve these problems are just a waste of time (at best, because they usually worsen the situation).

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  • Unfortunately, you have many questions here. While they're all related to your indoor air quality, they're all unrelated. 1) What kind of filtration system? 2) Are active carbon filters good for this? (somewhat related to 1) 3) How powerful a fan do we need? 4) Will a fan keep air from flowing back in? 5) Can we, with an improvised, DIY system effectively make a commercial level air scrubber? 6) Can we clean & dry inside air without opening a window in the first place? Frankly, I'd focus on #6 first, then address the others if the answer to that is "no".
    – FreeMan
    Commented Mar 8, 2022 at 18:40
  • @FreeMan thanks for your feedback, I reformulated my question and deleted my answer.
    – JinSnow
    Commented Mar 9, 2022 at 7:58
  • @ed-beal thanks for your feedback, I reformulated my question and deleted my answer.
    – JinSnow
    Commented Mar 9, 2022 at 7:59
  • @jsotola, thanks for your feedback, I reformulated my question and deleted my answer
    – JinSnow
    Commented Mar 9, 2022 at 7:59
  • They either need to come and make that window inoperable, or make the chimney higher. But if "institutions that are supposed to solve these problems are just a waste of time" then ... IDK... stop paying rent? Not sure of the laws in France.
    – Mazura
    Commented Mar 10, 2022 at 0:17

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