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DYI report: pressurized air filters at home and air quality

runcyclexcski profile image

Hi all,

Just a DIY project update. I finished installing a pressurized HVAC HEPA-charcoal filter system for my flat, to control allergens and odors which trigger my asthma. Before, it was implemented only for the bed I slept in (and stayed in for the last 3 months, almost). Now it's the living room, the kitchen, and the bedroom. Looks clunky, but my wife tolerates it so far (better than calling AE every week). The system allows me to get out of bed and get things done about, like wash dishes, w/o --finally -- wearing a respirator at all times.

Below I show particle counts for the air quality from today at LE2, compared to the particle counts inside the flat. The system is for allergens and pollutants, not for covid. But, just for reference, a covid virion is 100 nm. Viral particles tend to travel in droplets ~1 micron. Smallest pollen is 3 micron, I believe, and mold spores are about that size, too. Pollen also might explode and release smaller particles; diesel soot is covid-size.

The key observable is the ratio of counts in the same channel in different conditions, not the absolute counts. The 2.5 micron channel is the one we see in the news.


Outside air at LE2:

0.3 micron -- 48,299

0.5 micron -- 11,431

1.0 micron -- 1,849

2.5 micron -- 282 (channel reported in air quality reports)

5.0 micron -- 27

10 micron -- 11


Inside the living room

0.3 micron -- 473

0.5 micron -- 132

1.0 micron -- 19

2.5 micron -- 0 (channel in air quality reports)

5.0 micron -- 0

10 micron -- 0


In the bedroom at the head board (next to the system outlet):

0.3 micron -- 0

0.5 micron -- 0

1.0 micron -- 0

2.5 micron -- 0 (reported in air quality reports)

5.0 micron -- 0

10 micron -- 0

Conclusion: a 100x reduction across all channels compared to the outside air in the living room, and no detectable particles at the filter outlet. It worked better than I expected: I would be happy even with a 10x reduction (10x safer to be inside than outside in the "fresh" air). Sampling was for 20 sec at 2.8 liters per minute. Airflow is about 300 m^3 hr^-1, power consumption is about 200W (1/10 of an electrical kettle, but it's on 24-7) -- about 3 air exchanges per hr. Humidity has so far stayed between 40 and 50%. The intake is from the outside, so no stale air and no humidity build-up. All doors and windows are sealed , i.e. the only way the air gets inside is via the system (and whenever we need to get mail or go to work). Heating is a bit of an issue, I have installed an electrical heater, but have not tried it yet.

Another note: "outside air" counts can vary 20-fold from day to day, due to variable air quality. I bet the air in London would be 10x worse on any day.

9 Replies

That is so impressive!

runcyclexcski profile image
runcyclexcski in reply to Poobah

just wanted to share in case someone finds this forum years later (and something happens to me by that time :) ) Could post this to Instructables, with part numbers and engineering drawings but not sure if they want this.

That’s quite amazing. Are you going to take it further?

forgot to say that I am also making a powered respirator now. So that I can work while wearing it. While wearing it, it looks like the "Immortal Joe" character from "Mad Max. Fury Road". It's a cultural reference my students recognize, so I am happy with it.

There is not much further to take this, it seems to work. But when we move to a new flat I will do it a bit differently. I would use steel round ducts, b.c. flexible ducts are easy to puncture, resist air flow, and make noise. I need to arrange the filters on a rolling cart, so that they can be moved to another flat as a single unit. The new flat/house would need to have taller ceilings (like office buildings do) to allocate the space for the ducts. The ducts need to go between rooms via walls, not via doors.

We have a system and it’s definitely helped my asthma.

angievere -- may I ask what filters you use and whether you have had issues with odors from the filter?

I used to rely on IQAir for everything, but their recent HEPA filter batches have a strong odor which does not dissipate with use (and which they deny is even there). Thankfully, their units are modular and the filters are relatively standard size (310x310mm). Turns out, 3M Filtrete 1500 12"x12"x1", if two of them are stacked in series, are OK particle count-wise (all zeros in 20 sec, 3000+ reduction). FIltretes have no odor, and are 5x cheaper than IQAirs, while still a respectable company (3M is not going anywhere). FIltretes do require frequent replacement, and introduce more air resistance to the motors than HEPAs. Still, got to have them as a backup (I order in bulk).

I also got a HEPA box from a Turkish company (OZCON) for £150 for a 305x305x150mm. Their filters have stainless steel frames, and are very robust. No odor from their filters.

Another issue is that filter companies go out of business all the time. If they do, and if their filters are a strange non-standard size, one is stuck with a useless unit. Hence my method of getting modular units of standard size (square filters, not round or other strange shapes) which one can rig with other filters using Kapton or Aluminium tape. I also started ordering large . This way I have supply if there is a major accident with air quality issues, like fires in CA. No fires in the UK so far, but one never knows. Climate is changing.

Finally, thinking to get a backup generator. This starts to sound paranoid, but my life depends on these filters now.

Sorry, I’ve only just seen this. It’s a mechanical ventilation system with heat recovery - I’ve no idea about the details. My husband fitted it throughout the property when we had an extension - it was expensive so he brought the system and fitted it himself with help from a plumber.He cleans the filters regularly and has never mentioned a smell…

It’s made such a difference to the air quality and has definitely helped my asthma.

Apparently my husband washes the filters that came with the system.

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