Section 3: Buying an air purifier

Now that you know what kind of air cleaner you need (and what kind of air cleaner to avoid), you're ready – almost. There are several things to consider before you go buy an air purifier. These factors and features can be the difference between a great air purifier, a lousy air purifier, and one that's just so-so. Armed with knowledge of these critical considerations, you will be able to choose an air purifier that is right for you.

1. Area coverage

This one looks like a no-brainer. Air purifiers can handle different size rooms, so you'll need to pick one that covers an area about the one you're intending to use it in. However, it's not as simple as it looks. Manufacturers and retailers often advertise square footage that far exceeds ideal operating conditions. If you're running an air purifier because you have allergies or asthma, you'll want to make sure you get 4 air changes per hour at the very least, preferably 6 or 8. A retailer may be advertising square footage for the fewest number of air changes per hour, which would be 2 – not sufficient for allergy and asthma sufferers, and not a huge improvement in air quality.

So how do you know? The quantity of air a unit can handle is primarily based on fan speed, which is measure in CFM – cubic feet per minute. If you're the calculator type, it works like this:
1. Multiply CFM x 60 for cubic feet per hour.
2. Divide by the number of desired air changes (4 or 6).
3. Divide by 8 (or 10 if you have tall ceilings.)
The resulting number is an ideal area for that air purifier.

If you're not the calculator type, here's a quick guide: A 400 cfm fan will change the air twice for a 1500 sq. ft. room, 4 times for 750 sq. ft., and 6 times for a 500 sq. ft. room. A 200 cfm fan will change the air twice for a 750 sq. ft. room, 4 times for a 375 sq. ft. room, and 6 times for a 250 sq. ft. room.

Another thing to keep in mind: most air purifiers have several fan speeds. Square footage is calculated based on the highest fan speed (which has the highest CFM). But the highest fan speed is also the noisiest, so most people run their air purifiers on one of the lower settings. Calculating a square footage based on a machine's lower CFM is probably more realistic for typical usage.

With these caveats, you can see that an air purifier advertised to cover 1500 sq. ft. may be much more ideal for a room that is 250 sq. ft., in realistic usage by a typical noise-hating allergy sufferer.

Note: This applies to air purifiers that use mechanical filtration, i.e. fans which draw air over various filtration media. Using an electronic air purifier which emits ozone in a room smaller than it is intended for can be very harmful to your health.

2. Filter Replacement - Cost and Convenience

Some filters are easy to replace. Some are not. Some filters are less expensive, some are more so. Some need to be replaced every six months, while others last three to five years. Before you purchase an air purifier, ask:

1. How much do replacement filters cost? This includes HEPA filters, carbon filters, prefilters, UV bulbs, anything that needs to be replaced.
2. How often will the filters need to be replaced? If your unit includes both a HEPA filter and a carbon filter or other combination filtration media, they will probably need to be replaced separately, and may last for different periods of time. This can be a hassle, particularly if they are difficult to access.
3. How do you replace the filters? Some filters are easy to replace and you can simply pop them in. Some require a little more effort and will require tools. On the other hand, loosening 4 screws once every few years may prove less of a hassle than popping in a new filter every six months. Just make sure you know what you're in for before you get your air purifier home.

3. Energy costs

This is a factor that few consider until they get their air purifier home – and their electricity bill takes a hike upwards. Unlike most household appliances, an air purifier is one you'll want to run almost continuously. So, before you purchase one, you'll want to make sure that you can run it continuously, without going broke. Most air purifiers will be advertised as economic and energy efficient (and if you find one that isn't, you'll definitely want to investigate further). But don't simply accept the retailer's claims – any air purifier should have technical specs available, with power consumption listed in wattage. If only volts and amps are listed, simply multiply the two: volts x amps = watts.

For those calculator types: the wattage of an appliance, divided by 1,000, multiplied by the number of hours used per month, equals your kWh (kilowatt hours, or 1,000 watt hours). Multiply that by your cost per kWH (usually between 7 to 10 cents, depending where you live) and you have your operating cost per month.

For those who are less mathematically inclined, simply know this: typical mechanical air filters can use anywhere from 50 watts on low to 200 watts on high. (For comparison sake, a typical lamp is about 60 watts, while a typical computer is about 365 watts). If you're choosing between two air purifiers, make sure you compare the energy costs necessary to run each of them, at the most likely fan speed.

4. Noise Level

This is probably one of the most discussed features of mechanical filtration air purifiers, so you're probably already aware that it's a consideration. Some air purifiers are much quieter than others, although generally noise level and power go hand in hand. Noise level is quoted in terms of decibels, or dBAs.

If possible, ask for a demonstration before you purchase an air purifier, so you can make sure that the noise level is something you can stand to have in your bedroom at night. (Some people find a low level white noise to be very soothing when they sleep, but not everyone is like that.) However, if a demonstration is impractical, here is a little chart to give you an idea of what you're talking about – and what 45 dBA actually means in practical terms.

35 dBA
A quiet room. A little quieter than the hum of an average computer.
45 dBA
A forced air heating system. The hum of the refrigerator.
55 dBA
A bathroom exhaust fan. About the noise level of a clothes dryer.
65 dBA
The dishwasher. Or the washing machine.
75 dBA
Going 30 miles an hour with the car windows open.

5. Usability features

These are the bells and whistles. They can make your air purifier a lot easier to use. On the other hand, they can also significantly up the price on an air purifier that isn't really all that much better than the next one. You simply have to decide which features will make your life a whole lot easier; and which ones just aren't worth the extra cash. Here are some examples.

If you have trouble keeping track of time, filter change indicator lights can be extremely helpful; they can help prevent you from running an air purifier after the filter has become clogged, which doesn't do much for air quality. That being said, there are some things to consider about filter change indicator lights. Most filter change indicator lights work on a simple timer – they keep track of the length of time the unit has operated, and they turn on the light after a certain length of time. This is a general guide, but depending on how dirty the air in your home is, the filters may last a longer or shorter length of time. A timer only measures how long they have been used, not whether they are dirty. There are more accurate ways of measuring if the filter is actually dirty or clean, but these are much more costly and the first method is far more common.

These don't sound all that important until you're trying to transport a forty or fifty pound air purifier. Then those casters sound mighty useful. Some air purifiers are very heavy, especially units with heavy-duty carbon filters. Casters can be great for repositioning your air purifier inside a home or building, or moving it on flat surfaces – obviously they are not so helpful if you have to move your air purifier up and down stairs. Keep in mind that handles, or a place to grip, are also extremely useful in moving an air purifier from place to place, even in situations where casters won't help.

6. Reputation and Warranty

A manufacturer's reputation, and the experiences by past customers, deserve consideration in your decision. Certain manufacturers and products are highly respected in the industry for a reason – and the same goes for products which have garnered less respect.

And last but not least, consider the warranty. A five year warranty is a good one. A ten year warranty is even better. Take into account what the warranty covers – motor, fan, electrical components? Also, what customer actions will void the warranty? Some manufacturers will void the warranty if the customer does not purchase replacement filters over the recommended time period. This can be unhandy if you plan to run your unit less often or if the air in your home is cleaner than average. You can end up paying for replacement filters even if you don't need them. Just a tip to keep in mind.

You're ready to go! You've identified your contaminant, chosen your filter, and discovered some important considerations while shopping for an air purifier. But just in case you need some more information, here is a helpful glossary of terms and terminology used in the air purification industry. Knowing these will arm you with a whole lot of knowledge in comparing air purifiers.

Seen on Extreme Makeover
Home Edition
The best air purifiers, by far, are manufactured by IQAir. The IQAir HealthPro has been featured on popular television shows, and is a bestseller.