Permanent Filter Air Purifiers
Filter Construction Comparison
A HEPA filter is comprised of millions of microscopic fibers** all packed into a dense media matrix. These fibers provide maximum surface area to capture particles of all shapes and sizes.
HEPA filters capture particles in two ways:
Particles are caught between fibers
like a sieve
Particles stick to fibers
there are various methods by which this happens but all of them lead to the particle sticking to the fiber naturally – no electricity, no extra technology is required
The one major downside? Due to their microscopic size the fibers comprising a HEPA filter are impossible to clean. A HEPA filter is always replaced. Never cleaned.
The best example of a permanent filter is Honeywell’s IFD filter. IFD filters feature a dense honeycomb design. Contacts on each side of the filter allow for an electric charge to be imparted to the filter. The filter holds an electrostatic charge which works like a magnet to pull particles out of the air as they travel through the filter.
The one major downside? Well, there are many. Let’s take a look.
Major Downsides to Permanent Filters
1. Unproven and no industry standard.
HEPA filters have to be manufactured to a certain standard. That standard is that they have to be able to remove 99.97% of particles larger than 0.3 microns in diameter. If a filter doesn’t meet this standard, it cannot be called a HEPA filter.
MERV is widely accepted and used in the HVAC and air filter industry. MERV operates on a numeric scale starting with “1” and ending at “20”. The higher the MERV, the greater the filter’s efficiency. A MERV 20 filter is more than 99.999% efficient. A MERV 1 filter is less than 20% efficient.
A MERV 17 filter is 99.97% efficient. It’s otherwise known as a HEPA filter. Where does the HEPA moniker come from? Look at what it stands for.
“MERV” stands for “Minimum Efficiency Reporting Value” and “HEPA” stands for “High Efficiency Particulate Air”. A HEPA filter is simply a super high efficiency air filter.
Permanent filters are not rated or tested to these same standards. If you purchase an air purifier with a permanent filter, you’re relying on the individual manufacturer to provide you with accurate, precise and complete testing information on that particular filter.
What happens when you do that? Let’s take a look:
Honeywell claims that the IFD filter installed on the HFD120Q “effectively removes up to 99% of airborne allergens, 2 microns or larger”.
They claim that the IFD filter installed on the Air Genius 5 “removes up to 99.9% of airborne particles 0.3 microns or larger”.
Here we see a difference in claimed efficiency for a filter with the same name “IFD” name in both units. Also note the language in the claim. The claim is made that the filter removes “up to” a certain percentage of particles. So it can be 50% at times, 70% at other times, and “up to” 99 or 99.9% at other times.
There is no difference in efficiency between two HEPA filters. A HEPA filter must have an efficiency of 99.97% to be called a HEPA filter. There is no “up to” when it comes to HEPA filters. It’s 99.97% or it’s not a HEPA filter. There are no claims to worry about other than that the filter is in fact a HEPA filter. If it’s a HEPA filter you’re good to go. No guessing, no questioning, no lack of surety is involved as it is with permanent filters.
2. No commercial scaled up equivalent.
HEPA filters are used in a myriad of different commercial applications, including hospitals. Permanent filters are not.
When you buy an air purifier equipped with a HEPA filter for your home you can be confident that the same type of filter you’re using to clean the air in your home is used to clean the air in places where it matters most.
The same cannot be said for permanent filters. For example, Honeywell’s IFD filters are exclusively used in their line of residential air purifiers.
3. Loss of efficacy after continued use.
Both HEPA filters and permanent filters have a limited amount of surface area available to capture particles.
The difference is that HEPA filters have a lot more surface area to work with. Recall that HEPA filters are comprised of millions of microscopic fibers that provide a tremendous amount of surface area.
The honeycomb design of permanent filters definitely improves their surface area vs a non-honeycomb design. However, there are no millions of microscopic fibers here. The surfaces that collect particles are flat.
The much greater surface area of HEPA filters allows them to continue to be effective well after a good amount of particles have been captured.
The same cannot be said for permanent filters. They “saturate” much faster due to their much lower surface area.
4. More maintenance.
Because they “saturate” with particles faster, permanent filters have to be cleaned much more often than HEPA filters need to be replaced.
It also takes much more time washing and vacuuming a permanent filter than it takes to throw a used HEPA filter in the trash and replace it with a new one.
This means that you’ll spend much more time much more often having to go through process of removing, cleaning, and replacing a permanent filter than you will removing and replacing a HEPA filter.
5. No guarantee that filter is back to 100% efficacy after cleaning.
A permanent filter, when brand new is completely clean and is therefore 100% as effective as it can or ever will be.
After you wash and vacuum it, it will never be restored to that brand new state. There will always be a bit of particle build up left behind. Why? Because of its honeycomb design. There is no way to even properly inspect the interior of the honeycomb style filter to make sure that it’s clean after you clean it. You can’t properly see inside of it. And even if you could there would be no way for you to verify that all particles were removed with the naked eye. Most particles are of a microscopic size – well below what you’re able to see with the naked eye.
When you replace a HEPA filter you’re 100% guaranteed that the filter is 100% as effective as a HEPA filter can be. Why? Because you know it’s brand new.
The Bottom Line
Particle filtration is the primary reason you’re buying an air purifier. The air purifier’s filter is the primary component that enables it to filter particles. HEPA filters work. They’re made to work to a certain standard. They work so well they’re used commercially. They stay effective for a long time and they require no maintenance other than removing them and replacing them.
The same simply cannot be said for permanent filters.
If you’re going to go through the trouble of purchasing an air purifier and running it on a consistent basis to improve air quality in your home, the best way to do it is with an air purifier equipped with a HEPA filter. Permanent filter units are not recommended.
** HEPA filters are usually comprised of a combination of glass and polymer fibers. The glass fibers are generally smaller in diameter than the polymer fibers. Glass fiber diameter can be as low as 0.3 μm (micrometers) while polymer fiber diameter generally stays in the 10 μm range.
The glass fibers provide maximum surface area while the polymer fibers provide structural support. This structural support is necessary as all HEPA filters are pleated. Glass is brittle enough to break when pleated. Adding polymer fibers to the media matrix keeps the structure sound.
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