DIY Air Purifier in 24 hours

February 19, 2025

Air pollution in Delhi has been quite terrible recently, and it is also pollen season in Bangalore, so air quality and allergies were quite the hot topic on my Twitter feed.

Prasun posted recently that he’d built an air purifier for himself at home. It seemed easy enough to do, and while there weren’t promises of “single digit AQI” it had the promise of bringing it down drastically.

What you need

  1. Mi Air Purifier HEPA filter. You could probably use something else, but the rest of the build works well with the shape of this particular filter
  2. 6 inch exhaust fan. It’s a fairly standard sized product used for kitchen exhaust fans, so any 6 inch exhaust fan should do.
  3. A 2 pin electrical plug, from your local hardware store and electrical wire, to connect the fan to the power outlet
  4. I 3D printed a “coupler” part so that the fan and the filter fit snugly but could also be detached easily. Link to it is here. You could also just use double sided tape if you don’t have access to a 3D printer. The coupler is printed in two parts, to reduce the print time and wastage. You just have to glue the flat sides together after printing using Fevibond, let it sit for a few minutes, and the part should be done.
  5. A Smart Plug of your choice, so you can switch on and off the purifier using your favorite home automation platform

Steps to assemble

The image above is fairly self explanatory, so I’ll only focus on the things of note.

  1. Make sure the purifier sucks in air through the filters and pushes it out through the top. The air purification is more effective that way since the air is pulled in uniformly from all sides. It is also less damaging to the filter itself in the long run since the fan isn’t pushing at the material at all times

  2. The fan can get a bit noisy, depending on how sensitive you are to sound. The way I handled this was to run the filter at fixed times in the day instead of all day, running it before going to bed and while we were most likely in deep sleep. This drastically reduced the perception that it was “very noisy”. Another way to do this might be to use a fan PWM controller so you could slow down the fan. This will reduce the noise and slow down the rate of purification.

  3. The 3D printed coupler is designed so that the part rests comfortably on the Mi Air Filter, and the fan can be slid onto the top of the part. This allows for easy cleaning and replacement of any of the parts. The files can be downloaded here and here