With air pollution now causing 13% of deaths in the USA, the use of air purification is becoming more common. Unfortunately, air purifiers do need some basic maintenance to make sure that they keep indoor air quality high. The particulate filter, the HEPA air filter, which traps tiny particles becomes blocked with particles and needs changing periodically. The activated carbon filter, which removes many chemicals from the air, also needs changing every so often. Unfortunately, they usually need changing at different times. Rarely a manufacturer produces an air cleaner which has permanent filters, but almost all air purifiers will need a replacement filter at some stage.
On average an air purifier filter will last 12 months. However there is a large range from 6 months and 50 months. It is important for the effectiveness of the air purifier to stick to the recommended schedule of filter changes.
Different air filter types within the same air purifier need replacement on different schedules depending on which airborne pollutant that they deal with. In general activated carbon filters need replacing more frequent than particulate (HEPA) filters. Overall, the longer the filters last, the fewer times you have to open the machine and replace them.
The schedule for air filter changes for various air purifiers is shown in this table-
|Manufacturer and Model||Filter Type||Filter Change Frequency|
|Germ Guardian AC4825||Filter||6 months|
|Levoit Core 300||Pre Filter||6-8 months|
|True HEPA & Activated Carbon Filter||6-8 months|
|Coway AP-1512HH Mighty||Odor (Carbon) Filter||6 months|
|True HEPA||12 months|
|BlueAir Blue Pure 221+||Particle/Carbon Filter||6 months|
|Honeywell HPA 300||Pre Filter||3 months|
|iQair HealthPro Plus||PreMax Filter||18 months|
|VOC Filter||24 months|
Air filter costs vary significantly from one air purifier to the next. It is possible to buy a small air purifier because it is cheaper but find that it needs more frequent filter changes so that after two years you have paid more than if you bought a slightly more expensive larger machine which needs fewer filter changes. Thereafter the small machine will be continually more expensive to maintain. This is not always the case, but it is wise to calculate the cost of buying filters over 5 years when comparing machines.
The function of air purifier filters does deteriorate with time and so the HEPA filter will need changing. Otherwise, you could be breathing in air with more particles in it than you intended. However, as the effect on your health largely depends on the number of particles in the air some people feel that it is logical to only replace the filter when the concentration of particles in the air coming out of the filter increases.
How do you know when to change the HEPA filter?
There are 3 methods-
1) Use the time the filter has been operating and the fan speed to estimate when it needs replacement.
This assumes that there is an average amount of dust in the environment in which the air purifier is working. This may be communicated to you either via of Wi-Fi notification or by lights on the air purifier itself.
It is base on data that the manufacturer will have collected from testing many machines under scientific conditions. It is however, based on an “average” amount of dust in the environment and you have no way of knowing whether your home has an average or greater or lesser amount of dust. The manufacturer has two other pressures on them which will make them err on the side of recommending earlier rather than later replacement. The first is ensuring that the filter is definitely still working well when it is replaced so protecting your health. The other is that if they recommend earlier replacement, they will sell more filters.
2) Use a sensor built into the purifier by the manufacturer
The other mechanism is by incorporating a particle sensor into the machine which detects the deterioration in the filter and lets you know when to change it. The problem with this is that the particle sensors in the machine need to be inexpensive. They usually use an LED and photodiode, these have a very poor signal-to-noise ratio, and hence tend not to be very accurate. So this is not recommended. However, you could buy a more accurate particle counter and consider method 3-
3) Use a Particle Counter to Assess When to Change the Filter?
It is probably best to follow the manufacturer’s instructions on HEPA filter changes-these however may not be relevant to your current circumstances. The instructions will be for an average consumer but your air may have a lower amount of pollution in it and the filters may need to be changed less frequently. To gauge when you should change the HEPA filter you may wish to buy a particle meter to see when the air coming from the filter has deteriorated and the particle count in it has increased.
However, you would need an accurate particle counter and need to take a reading when the air purifier is new so that you know what the reading is with new filters.
Dylos sell a particle counter and one of the advantages of their particle counter that they point out is that you can check your filters and read to use the frequency at which you changed them. In this way, you can save the cost of the particle counter over time and then continue saving money on filters. Other particle counters starting at $35 can be found in this article.
Even if the air coming out is clean when you test it with a particle counter how do you know that the filter as it gets blocked up the air purifier is still providing an adequate flow of air? One way would be to check the air quality in your room when the filters are new as a baseline and then you will be able to tell if the air quality is deteriorating because of a low flow of air through the purifier even if the air coming out of the purifier is excellent.
Another sign of the filter blocking and the machine is having difficulty pushing air through the filter is that machine starts vibrating. Or you may notice that the air flow has decreased when you put your hand next to the outlet.
A reason for following the manufacturer’s guidelines is that any particle meter that you buy will not be able to measure ultrafine particles as laser particle counters cannot detect particles at less than 0.3um. As the filter clogs up and the pressure forcing the air through the obstructed filter increases the velocity of flow through the unobstructed areas of the filter will increase. This would make it more likely that ultrafine particles can get through the filter.
However, if you could pick up a cheap used P-Trak 8525 particle counter this would absolutely be a feasible strategy. Unfortunately, this is not likely to happen. This meter can measure ultrafine particles. See the video in the article on the iQair HealthPro Plus for testing testing an air purifier with this meter.
Volatile Organic Compound (VOC) Filters-Filters for Chemicals and Smells
It would be possible to buy a meter to detect volatile organic compounds and then change the activated carbon filter only when the purifier is failing to remove them. One problem with this approach is that the meters only detect formaldehyde and a small range of VOCs. So there may be other pollutants which the filter is so old that it will not absorb and the meter would not be able to alert you to this.
Also, this selective change of one filter would only be possible for some purifiers. Many of the smaller air cleaners often come with activated charcoal filter and particulate filter built as one unit. In general purifiers do not have inbuilt sensors for VOCs.
So for the VOC filter, which is usually an activated carbon filter, it is best to follow the manufacturer’s instructions.
One company, SmartAir have a different approach to assessing the time to change carbon filters. They make the very valid point that different homes will have very different amounts of VOCs in the air. Therefore the air purifiers in different homes will in reality need very different amounts of time between changes of the activated carbon filter. They suggest periodically removing the filter from the air purifier and smelling it by putting your nose within an inch of it. If it smells acidic, sour or chemical then it is time to change it.
Air purifiers need periodic changes of filters, the time between filter changes varies for each air purifier and also both main filter types. You should calculate the cost of filter changes over the next 5 years for an air purifier before buying it. Sometimes it will be cheaper to buy a slightly bigger machine with that needs fewer filter changes.
It is probably best to let the air purifier tell you when to change the filter on the basis of the time that it has been filtering the air.