How to Know When to Change Your Air Purifier’s HEPA Filter?

When to change your HEPA filter can be a difficult question to answer. I’ve always questioned those numbers that air purifier companies give you. Where do those HEPA filter replacement numbers come from?

How often should I change my filter?

If a company that’s based in Switzerland is telling you can use it for six months, is that Beijing air? Is that Delhi air? If it lasts six months in Switzerland, is it really going to last six months in Delhi?

India pollution
Smart Air Founder Thomas Biking in Delhi

Add in the fact purifier companies are incentivized to have you replace your filters more often for profits.

So, I’m a bit wary of how companies get to their filter replacement numbers.

Lack of Transparency From Air Purifier Companies on HEPA Replacements

I had a difficult time finding any data-backed explanations for the HEPA filter replacement recommendations from many of the big brand air purifier companies.

So, I decided to contact the popular brand Medify Air to ask them about the basis of their recommendations. Surely they would have data to back up their claims somewhere right? Or else they would be misleading their customers providing meaningless recommendations.

Notice their response: “We do not share test results or publish data on the lifespan of our HEPA filters for proprietary reasons.”

When to change your HEPA filter (Medify Air)

Factors That Effect How Long Your HEPA Lasts

How long do the Blast and Blast Mini HEPA filters last?
Smart Air’s Chief Nerd Scientist Paddy

In reality, there are many factors that determine the lifespan of your HEPA filter. These factors include:

  • Hours used in a day
  • Speed used
  • Outdoor air pollution levels
  • Indoor air pollution sources (such as cooking)
  • Pre-filter frequently vacuumed or not

This makes when to change a HEPA filter vary greatly amongst users. So, it is impossible to give a specific HEPA filter replacement timeline that is ideal for all users.

BUT, at the very least, companies should explain and publish open data on where they got the numbers and not leave customers in the dark.

Watch: Smart Air Founder Thomas Talhelm on Filter Replacement Recommendations
How Much Should Clean Air Cost? Innovating Affordable DIY Purifiers - Thomas Talhelm

How to Know When to Change Your HEPA Filter

The best way to know when to change a HEPA filter is by using a PM2.5 air quality monitor, also called a particulate counter. An air quality monitor can be used to ensure the air in your home is at safe levels.

A HEPA filter’s performance reduces over time. By periodically checking your air quality, you can replace your filter not too early, but also before there is a major reduction in filter effectiveness.

Read More: How to Use an Air Monitor to Determine When to Replace a HEPA Filter

And the good news is you do not need to spend thousands of dollars on fancy equipment.

Our analysis shows there is no correlation between price and accuracy for air quality monitors. In fact, the $70 monitor tested outperformed the over $7,000 monitor.

Read More: Best Air Quality Monitors in 2021

How We At Smart Air Make HEPA Replacement Recommendations

At Smart Air, we test and publish the HEPA filter performance of our air purifiers over time. For example, our Sqair purifier (designed for living spaces) was tested on high for 1500 hours in Beijing air.

When to replace an air purifier's HEPA filter

There was a 50% reduction in HEPA filter effectiveness after 1400 hours of running on high.

Sqair HEPA lifespan test in real Beijing air pollution

Therefore we listed the Sqair HEPA filter lifespan as 175 days. This is based on running the Sqair on high for 8 hours a day in Beijing air.

We have run similar tests for our purifiers for larger spaces such as offices, schools and hospitals: the Blast and Blast Mini.

Bottom Line: How to Know When to Replace Your HEPA Filter?

There are many factors that determine the lifespan of your HEPA filter (location, speed used, time used, etc). Air purifier companies also often give little explanation for where they came up with their numbers. The best way to know when to replace your HEPA filter is with the use of an inexpensive air quality monitor.

Read More: Here’s how to use one to test your HEPA effectiveness.

Smart Air

Smart Air: Democratizing Clean Air

Smart Air is a certified B Corp committed to combating the myths big companies use to inflate the price of clean air.

Smart Air Team

At Smart Air, we provide empirically backed, no-nonsense purifiers and masks, that remove the same particles as the big companies for a fraction of the cost. Only corporations benefit when clean air is a luxury.


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Smart Air is a social enterprise that creates simple, no-nonsense air purifiers and provides free education to protect people’s health from the effects of air pollution. We are proud to be the only certified B-Corp dedicated to fighting air pollution.