Choosing a HEPA Filter Air Cleaner

Josh Feinmann, Clean Air Advice
June 2006

You've decided that a HEPA Filter air purifier is the right choice for you, now where do you start? The wide range of products—and prices—on the market can be overwhelming, but you can make a simple, worry-free decision by breaking it down into a few simple steps. Let the experts at Clean Air Advice walk you through the steps of How to Choose a HEPA Filter.

How Large is the Room?

HEPA filters, like most air cleaner products, are generally designed to clean the air in a single room. When choosing a HEPA filter air purifier, keep in mind the size of the room, and make sure the HEPA product's capacity does the job. Most air cleaner manufacturers express the cleaning efficiency of HEPA air cleaners in a "cleaning area" measured in square feet. That is, a HEPA Air Filter product rated to 400 ft² is recommended for a 20ft x 20ft bedroom.

Note that the square footage cleaning area also has a time factor figured in: the square footage figure is based on how many Air Changes per Hour (ACH) a certain unit can complete within its rated area. For general purposes, 4 to 5 ACH is recommended. For special conditions like severe pollution levels (high pollen counts, multiple pets, humid areas with mold, etc.), 6 to 8 ACH is a better bet. Similarly, if you or your family have high sensitivity to certain allergens, or suffer from asthma or other respiratory problems, we recommend choosing a HEPA filter rated well over the area you'll be using it in. In other words, make sure the coverage rating for the product is at least twice that of the room.

What Pollutants do you want to Clean?

While a HEPA filter is the most effective technology available for removing particulate matter and allergens from the air, they are not designed to remove chemical fumes or odors, or to kill bacteria, viruses, or other microbes. To extend their usefulness, many manufacturers include special features targeted on these other pollutants—meaning you don't have to skimp on particulate matter and allergen removal in order to get everything you need. "Hybrid" air cleaners might combine the standard HEPA filter unit with a chemical microbicide or UV lamp for neutralizing mold and bacteria, or specialized activated carbon or potassium permanganate gas-phase filters for removing formaldehyde, NO, sulfur dioxide or other noxious gases from the air. Less-sophisticated carbon-impregnated fabric filters or similar devices may be used for simple control of odors.

If general air cleaning and allergen control is what you're after, the standard HEPA filter air cleaner with no special add-ons may be just what you need. However, if you know there are specific irritants you need to clean, or if you must consider Multiple Chemical Sensitivity (MCS) situations, or even remove tobacco smoke and odors from living or work areas, make sure the products you compare have the capabilities you need. Chances are, no matter what specific situations you need to tackle, there is a HEPA air purifier for you—you just need to ask specific questions while you're shopping around.

How Much Does it Cost?

The initial cost of buying a HEPA filter air purifier is obviously a concern, and you should consider your budget when comparing models, but keep in mind that any HEPA filter, regardless of brand name, cost, or efficiency, can't function without periodically replacing the filter—and of course these filters cost money. Depending on the manufacturer, HEPA filter life spans vary greatly: while some must be changed every 6 months, a few claim to last up to five years! Most will fall into the 12-14 months range, and filters may cost anywhere from $40 to nearly $200. Much of the cost depends upon the coverage of the unit, and generally speaking, the more expensive filters do last longer. So, when comparing filter costs, make sure you compare units with similar coverage, and also factor the average cost over a similar time period. For example, compare the cost of two 6-month rated filters against 1/3 the cost of a 3-year filter. You may actually save money in the long run by choosing the "more expensive" machine.

In addition to the main HEPA-rated filter media, many HEPA and hybrid machines include "pre-filters" of various types which aid the unit in cleaning the air efficiently. Basically, the pre-filter catches large dust particles, pet hair and the like, preventing them from clogging the HEPA filter itself. In some cases, the pre-filter is a simple foam or fabric media that can be vacuumed or rinsed off and reused, though some must be changed at additional cost. If the products you are considering include any type of pre-filter, try to find a unit which allows you to change the pre-filter separate from the HEPA filter itself: the same goes for any additional filters such as a carbon odor filter or gas-phase filter media. Though they may seem more "convenient," you're usually paying more when you're changing all the filters together in one "cartridge," because you're likely replacing parts that don't need replacing at the same time. Keep in mind also that the addition of a pre-filter, or "dust filter" as they're sometimes called, often extends the life of the HEPA filter itself: it's better to spend $10-$15 three times a year for the pre-filter than to spend $150 to replace the HEPA filter which has passed on before its time. When all is said and done, make sure you factor in all the costs of running a unit at top effectiveness when you're comparing dollars and cents.

Of course you'll have to weigh your particular air cleaning needs against the additional cost of add-on filters and technologies: MCS sufferers might be willing to pay more for better chemical filtration, and those with severe mold allergies might find the microbial effectiveness of an additional UV lamp well worth the added cost. Again, to get the best deal, make sure you're comparing "apples to apples" when making your decision: you want a less-expensive air cleaner, not a "cheaper "one.

For a final word on the cost of running a HEPA air cleaner, you may be concerned about the effect on your power bill. You should keep in mind, though, that as far as power consumption is concerned, we're not talking about a major household appliance here. Some of the smaller units get by with a power consumption of 100 Watts or less, even on high speed—no different from a single 100W light bulb. By comparison, a typical refrigerator can consume up to 500 Watts or more; a water heater, as much as 3000. So even if you're running your HEPA filter continuously, the overall cost in terms of electricity is negligible.

Other Considerations

Once you've tackled the technical concerns behind choosing a HEPA filter air purifier, and done your cost accounting, there are still a few factors to think over. Like any household appliance on the market today, manufacturers of HEPA air cleaners offer their products in a wide range of finishes and colors to match your home décor, so there's no need to bring some bulky, industrial unit that would look at home on a Sci-Fi movie set into the living room—unless you want to. If style is a concern for you, you should have no problem finding a product that protects your lungs and is still easy on the eyes.

A more practical concern is noise: it may not seem like much of an issue, but when you're comparing coverage areas of HEPA filters, make sure you note the fan speeds of different models, along with their respective noise levels. That "400 ft²" model you just brought into your bedroom may be fine during the day, but if you can't sleep through the fan noise, you'll end up turning the fan speed down, and suddenly you're running a 200 ft² unit that just doesn't cut it. Typical HEPA units operate at noise levels anywhere from the "whisper quiet" 35dB models which really are almost silent in a normal home environment, to over 70dB—as loud as some vacuum cleaners or clothes dryers. If noise may be an issue for you, make sure the "quiet" or low-speed setting still moves enough air to cover your room.

Finally, it must be said that sometimes you really do "get what you pay for." Even at a retail store, you're probably going to raise some eyebrows if you take every product out of the box, remove the covers and filters, test the knobs and buttons, and generally make a nuisance of yourself in the home appliance aisle. And even though air cleaners and their fans are fairly simple machines, even the best, most durable products are occasionally going to break down. What you can look for is a decent warranty. You might save some money up front by going with a cheaper brand or "knock off," but what happens if it breaks? If the warranty doesn't cover internal parts or "wear and tear," or if there is no warranty at all, is it worth taking the risk? An electric fan that runs 24 hours a day can't be expected to last forever in the best of situations, so look for the most comprehensive, longest-term warranty you can find. You might even consider purchasing an extended warranty if the retailer offers it. After all, you're not going to save any money at all if you end up buying replacement units every year or two. When you consider the overall cost, you're better off buying the best HEPA air filter you can afford. That way you'll be breathing easier for years to come.

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