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Comment by chmars | Hacker News Reader

The filter durability is time-based in my experience:

I set up several air purifiers at the same time in December 2021 but used them in different areas, i.e., with different filter loads. The air purifiers ran 24/7 and mostly in automatic mode, except for some hours after known possible coronavirus exposures.

Official end of filter life was reached after about five months and for all filters on the same day. The air purifiers are still running tough, that's a plus!

Xiaomi recommends to replace filters every 6 to 12 months. The recommendation, however, is based on the use in polluted Asian cities, I guess. We have rather clean air here. I therefore assume that it is safe to use the filter for an additional few months.

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HEPA filters get more effective overtime in exchange for more restricted airflow. Thus the failure mode is "air is not flowing" and not "air is not getting cleaned".

At home I use 3 air filters in various rooms. These are standard/mid-range Japanese Sharp filters. Japanese because we live in Japan, not because Japanese HEPA filters are special. The filters themselves can be bought for about 30$ online. When the filters get near end of life I've had success by switching to a higher fan speed. This is not magic, at some point even on the highest setting airflow starts to match the old medium speed. The high speed mode consumes about 4x the electricity of medium speed.

The net result is there exists an intersection point where continuing to use a filter costs more money than replacing. For us in Japan with expensive electricity this point exists sometime after the airflow has diminished but the filter is viable on high speed. In cheap electricity countries the filter might become unusable before electricity becomes a significant cost.

> because we live in Japan

May I ask why you're using them at all? Every time I look at Japanese cities they seem to have PM2.5 levels in a second-digit microgram range. A bad day seems to be something like 15 µg.

Poor ventilation and a stir fry on medium-high heat will bring you above harmful levels for several hours in my experience.

Candles, cleaning, frying. All very good ways to increase air pollution in your home that nobody speaks about.

First off I don't want to under sell Japan, it is a pretty nice country and Tokyo is pretty clean. Sadly it's still a city with car pollution all cities have.

Unique to Japan is the pollen. After WW2 Japan was reforested in mass with a single variety of tree. Thus making the exact pollen release an annual torture test for anyone without air filters. My theory is everyone eventually gets pollen alergies, it's just a matter of time. My wife is affected during pollen season, and I've starting to notice myself become affected as well.

We do not stir fry, that's not a thing in Japanese cuisine. And our cooking is all IH so no gas particle. Yet even we will notice if the air purifiers are not running. We'll first notice our noises are a bit stuffy, and omly then check to find a kid has turned off the air purifier.

An upshot to low pollution is filters last ages.

>additional few months

Xiaomi filter processing Canadian air in a semi high traffic area after 2 years looks better than my Asian country filter after 6 months.

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