Cleaning HEPA [WAS} Re: Dust Mites

[Guest guest]

Barb and Ken,

Most air filter media isn't designed to be cleaned and cannot be

cleaned, especially HEPA, for a variety of reasons.

The cleaneable kind appeared mostly in furnace systems several years

ago. A few showed up in some room type units. They were created to

solve a fundamental problem with air filtration. The smaller the

particle to be removed the smaller you needed the pores in the media.

Like sifting sand through screenwire, the particles larger than the

holes were stopped but the smaller ones went right through. But the

smaller holes required bigger motors to force the air through them,

creating more cost and more noise. Or they could increase the size to

get enough holes, but then the filters wouldn't fit the equipment.

For furnaces someone came up with the idea of stopping particles

smaller than the holes with electrostatic charges. Like the

electronic ones but without the need to plug them in. They made

filters out of layers of different types of woven plastic designed

to create a static charge when air moved through them. The dust would

then cling to the charged material. Because they were plastic they

could be washed. Although the initial cost was anywhere from about

$45-200, that was the only cost.

They didn't work all that well for a variety of reasons but were

much, much better than the typical fiberglass matt. And much less

expensive than an electonic filter. HEPA units for furnaces were, and

still are, add-ons starting at $1200 or so, plus installation.

When 3M introduced the Filtrete material as a furnace filter they

were far superior to the electrostatic and you didn't hear

Harvey touting the cheap electrostatics anymore. Initial cost was

lower but at $14 per filter and needing to be changed every 4-6 weeks

created a long term cost greater than the washable ones.

Many of my clients tried vacuuming them to save money. But they were

then re-exposed to all the " stuff " the filter had removed from the

air. And the filter material wasn't resistant enough to withstand

cleaning. Washing destroyed them.

A HEPA filter cannot be cleaned. It is typically 1 foot by 1 foot by

1 foot, or other similar size ratios, with a tightly packed pleated

material rather than a flat panel. The reason is so the material can

be folded, giving it a surface area tens to hundreds of times larger

than a flat panel, sufficient to allow air through its very tiny 0.3

micron pores. Even then the forces needed are greater than a standard

furnace motor can handle.

The same is true for a HEPA in a room unit. The pleats are very deep

and very narrow and cannot be cleaned. One advantage to having such

a large surface area with deep pleats is it takes more than 4-6 weeks

for it to fill and become clogged with the tiny particles. Most

filter manufacturers recommend changing them every 3-5 years. If

conditions, such as in the new home you mentioned, Barb, are dirtier,

then they will fill more quickly. Maybe in only 6 months to a year.

But you must have pre-filters in front of it to remove the larger

particles, those above about 5-10 microns plus the giant visible

particles. If not, they clog the very fine HEPA quickly and you are

faced with an expensive replacement.

The manufacturer recommended frequency of replacement is based on how

long it takes to fill up. But what I've never been comfortable with

is that as the particles increasingly accumulate, so does the amount

of non-particle components (molecular, as in VOCs and some mycotoxins

and endotoxins). I'm not comfortable with blindly using HEPAs for

several years. If I start to notice an odor or any reactivity with

them, I'll replace the HEPA media. The odor and reactions then stop.

The primary objective with exposures is always to stop the reaction

by stopping the exposure.

1. The most effective way, ideally at least, is to identify the

source and remove the source. It's gone and there cannot be any more

reactions to it.

2. If that can't be done, the next best is to isolate the source with

sealants or air flow control. Painting a wall is a great way to

isolate the cat dander, for example. The source is still there but

you aren't exposed.

3. If those don't work or can't be sufficiently accomplished, then

the next best is to reduce the exposure by diluting it with

ventilation. It's (usually) cheap, but the source is still there and

the exposure still occurs, although at lower levels. Hopefully below

the level that triggers your reactions. You know by trying and

trusting your experience.

4. Finally, comes air filtration. It only " cleans " the air that

physically moves through it is, is expensive and has an ongoing cost

for replacing the filter media. Like ventilation, it only reduces the

levels in the air, hopefully below the level that triggers your

reactions.

That said, if air filters work as a first step, then that's all you

need. But if they don't then you need to start finding sources so you

can remove or at least isolate them. THEN if you still need help

because of insufficient removal or there are additional sources, a

HEPA may be the final touch.

But don't try to save money by cleaning them. It won't work and you

may damage the material. Then it won't be a HEPA anymore with tiny

pores. Instead it will have holes that are more like a vacuum cleaner

bag and we all know how they the create the light beams that Ken so

astutely noticed.

Carl Grimes

Healthy Habitats LLC

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> Carl,

> How often do you have to clean filters in a Hepa? I've heard problem

> with them is that they collect particles so they are only as good as

> how much they can hold before they aren't able to collect anymore. I

> would think new one in home previously didn't have one would have to

> have new filter replaced fairly soon in the beginning. I think Ken is

> referring to not seeing individual particles but collective particles

> being enough to create a hazy in air. I would think that could be

> particles smaller than an individual could see. However I still have

> air quality problems with home and I have no sunbeams in house,

> although I know what he is referring to. I ----- Original Message

> ----- From: " Carl E. Grimes " <grimes@...> > Also, HEPA will

> only remove dust that is in the air that goes through > the filter. It

> won't remove the dust that is coating the floors, > fabrics, walls and

> ceilings. All surfaces, in fact. So if those are > heavily loaded -

> even though still not visible - then the HEPA may > actually increase

> exposure for awhile because the air movement > disturbs the settled

> dust. The surfaces should first be HEPA vacuumed > so the HEPA air

> purifier has a chance to help >

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