Air Purifier Buying Guide: 10 Questions to Ask

A flower stand with a woman glancing at selection, this spring an air purifier buying guide will help you decide if you need to filter from allergens like pollen.

We recently released a guide on different air purifying technologies, but while the technology behind an air purifier may be an exceedingly important consideration, it isn’t the only consideration. If you want to buy an air purifier for your home, business, school, or healthcare facility, there are 10 other questions to ask yourself.

1. Do I Want to Address Particles, Pathogens, Odors, or Combustion Gases?

The single most important factor in choosing a purifier is what you want it to address. Different types of air purifiers can remove different contaminants.

Addressing Particulates

If you are looking to address small particles such as woodsmoke, cigarette smoke, cooking smoke, or any air pollutants that enter from outdoors, you’ll want a true HEPA filter. These air purifier filters have a MERV rating of 17 or greater and catch the smallest particles.

If you are looking to address large particles (such as dust, pet dander, pollen, or some dust mite allergens), you may want a True HEPA type filter, or you may want a mid-MERV rating fibrous filter depending on your fan motor power; (please see Question 9 below).

Another option for particulates is electrostatic precipitators. While these are unnecessarily complicated for most people’s needs, they can be of great use with older HVAC systems that can’t handle high-MERV.

Addressing Pathogens

Pathogens include bacteria, viruses, and sometimes mold spores.

For pathogens, we recommend using active purification. Passive purifiers (such as those which use HEPA without supplementary active technology) wait for the air to pass through their internal mechanism. This means that virus or bacteria particles can filter through your lungs before they are filtered by the filter.

Meanwhile, active air purifiers work by treating air in the room itself. Of the many varieties of active purification out there, we are going to recommend (you guessed it) ActivePure. Purifiers powered by ActivePure have been proven to reduce many types of viruses, bacteria, and fungi both in the air and on surfaces.

Addressing Odors

If you have new wood products, carpets, or furniture in your space, or if you do a lot of arts and crafts, then you could be releasing VOCs (volatile organic compounds) into the air. These are odiferous, carbon-based gases, some of which are harmful to human health.

ActivePure’s proprietary technology is also effective at neutralizing certain VOCs. Another powerful technology for absorbing gases and odors is activated carbon. ActivePure pairs with activated carbon in many of its machines to improve efficiency.

Addressing Combustion Gases

Combustion gases (such as carbon dioxide or nitrous oxides) are best handled by building improvements rather than cleaning the air. You should have your heater inspected annually, and you should ensure your stove vents to the outdoors. Though substances (such as Sofnolime) can absorb combustion gases, it’s much easier to prevent these gases from building up in the first place.

Dandelion seeds float away in sky, an air purifier buying guide helps you decide if you need one for this type of allergen

2. Do I Need a Portable Purifier or an Induct Purifier?

Did you know that purifiers can be built into your existing ventilation system? These are called induct purifiers, and they are an option for many homes, schools, businesses, and hospitals. Of course, you will want to get the right type of purifier for your ventilation system, as high MERV filters can put a strain on older systems; (please see Question 9 below).

If you don’t have an existing HVAC system, portable purifiers are the way to go. These are freestanding appliances, like your speaker system or microwave (only they look much cooler).

The advantages of induct purifiers is that they don’t take up space. If properly matched with the HVAC system, they also cover the entire building.

The advantages of portable purifiers are that they are portable (obviously); their visibility also reassures your guests/patients/students/customers that you are doing everything you can to ensure healthy indoor air quality. Portable purifiers may also be a more economical option, depending on the specific layout and needs of your indoor space.

3. Do I Need an Air Purifier in the First Place?

Another question you should ask is if you need an air purifier in the first place.

In light of the COVID-19 pandemic, we recommend that every space with high traffic and close interaction between people of different households invest in air purification. This includes all schools, hospitals, and businesses.

Whether you need an air purifier for your home isn’t as straightforward. If you live in an area with poor air quality (check your local reports), we would recommend investing in a purifier. The same is true if you have some source of contamination indoors, such as the aforementioned tobacco smoke, fireplace, or gas stove.

However, if you are a nonsmoker without a fireplace in a well-ventilated and maintained house with no pets in the countryside, you may not need an air purifier….unless of course that area has a lot of allergens. Or you have frequent guests. Or you cook fatty meats with a gas stove on high heat.

We suppose what we are saying is this: if you are a vegetarian hermit living on a houseboat built out of organic wood in the middle of the ocean, you probably don’t need an air purifier. This zephyrean ideal aside, however, many dwellings can benefit from the addition of air purification. If you are uncertain about your current needs, we recommend air quality testing.

A white row boat with pink roses around it, roses are a contrubting factor to allergens in the air

4. How Large of an Area Do I Need to Treat?

As you might guess intuitively, the different sizes of air purifiers suit differently sized rooms. Most manufacturers will say up front how large of a space (in cubic feet or meters) they expect a purifier to cover.

Of course, this requires you to know the volume of your room. To determine that, measure from the base of the floor to the ceiling, and measure the depth and breadth of the room. That should give you three numbers. Multiple these three numbers together, and you should have the volume of the room. (This only applies to rooms that are square or rectangular. Irregularly shaped rooms require additional calculations).

Keep in mind that almost every air purifier—save those for industrial use—is sized for a room with a maximum ceiling height of 8 feet. If your ceiling is higher than this, you may need a more powerful purifier in order for it to operate as intended.

The Association of Home Appliance Manufacturers (AHAM) has come up with a rating and testing system for portable purifiers called CADR; (note that CADR does not apply to induct purifiers). CADR stands for Clean Air Delivery Rate, and it tests an air purifier’s ability to remove smoke (representing small particles), dust (representing medium particles), and pollen (representing large particles). CADR is determined separately for each of these contaminants, so you will see three numbers on CADR-certified machines.

CADR is calculated thusly: “the rate of contaminant reduction in the test chamber when the unit is turned on, minus the rate of natural decay when the unit is not running, multiplied by the volume of the test chamber as measured in cubic feet.”

Wait, don’t fall asleep! We'll explain; an air purifier is placed in a 1008ft3 chamber and turned to maximum fan speed (if applicable). The chamber is then filled with a contaminant, and the air is tested after the air purifier has had time to remove the contaminant. Since AHAM knows how quickly each contaminant breaks down on its own (23-27 hours), they subtract this number from how long the air purifier actually took to clean the chamber. They multiply this success times the 1008ft3 volume and divide by 60 to achieve the CADR ratings.

Say a chamber was filled with smoke which would clear naturally in 23.8 hours. Say also a given air purifier cleaned the chamber in 2 hours. That would give a success rate of 21.8 hours. (21.8 x 1008)/60=366.4. So that air purifier would have a CADR rating for smoke of 366.4.

The max CADR rating a machine can receive is 450 for dust/pollen and 400 for smoke. For passive purifiers, you should look for an air purifier with a CADR rating at least 2/3rd of its CFM. (CFM is the amount of cubic feet the air purifier moves per minute.)

5. What’s My Budget?

This may seem self-explanatory; after all, there’s no urgency to put something on the credit card if you’ve lived this long without it. However, make sure you are saving up for an air purifier which will actually solve the problem you are looking to solve. There’s no sense going with the cheapest option if it is not right for your room size or the types of contamination present. Similarly, don’t rush to expensive solutions when a more economical option will do.

6. Does the Purifier Generate Too Much Ozone?

Many types of purifiers generate ozone as a byproduct. Ozone is wonderful in the upper atmosphere, as it shields us from UV rays. However, it can be irritating and even dangerous at ground level.

Note there are also types of purifiers which intentionally generate ozone to remove odors from flood or fire damage. These machines have their uses in unoccupied spaces, but we recommend these only be used by a professional.

Ozone may be generated any time that the air is energized, such as is the case with UV light, plasma purifiers, ionizers, and electrostatic precipitators. In recent years, modifications have improved most of these methods to reduce their ozone generation capacity to acceptable levels. However, some do still emit too much. The California Air Resource Board tests air purifiers to see if they emit less than 0.050 ppm, and also tracks a noncomprehensive list of intentional ozone generators. Over 20 purifiers with ActivePure Technology are CARB-certified.

White flower sitting next to red lit red candles, both contribute to air quality control from an Air Purifier

7. How Quiet Is It?

Many air purifiers have fans and motors, either to draw air through a filter or to send purifying particles out into the room. Depending on their size and efficiency, these fans can be loud or whisper quiet. According to the UK firm Quiet Mark, you’ll want an air purifier that blends the motor and the fan sounds into seamless white noise. Air purifiers with fans may list the sound (in decibels) a product produces on their spec sheet. If so, this will help determine if the purifier is right for you. After all, you don’t want a purifier designed for a warehouse to live on your nightstand.

If you do buy a louder purifier, placing it in a room with carpets, curtains, and cloth furniture may cut down on its auditory impact.

If you are buying a secondhand purifier (not recommended), older models tend to be noisier than newer models.

Some purifiers are entirely fanless as well. These can be an option for smaller areas.

8. How Often Does It Require Maintenance?

This is an important question. Nearly every type of purifier requires some maintenance and repair. Any purifier with a filter will need that filter to be changed regularly. Filter life cycle will vary widely depending on the filter’s MERV rating and the contaminants in the room. The same is true for activated carbon or chemisorbant media. In general, you should change true HEPA filters once every 3 months to 1 year and activated carbon filters every 3 months depending on the amount of carbon in the filter.

Meanwhile, needlepoint ionizers will need to be cleaned every 1 to 2 years; electrostatic precipitators need to be cleaned 4 times per year.

Filters with UV bulbs (including ActivePure) will need to be replaced every 5,000 to 9,000 hours, which translates to about every 7 to 12 months if operated continually.

9. What Are the Energy Costs?

This may come as a surprise, but even the least efficient portable purifiers only increase electrical bills by a few cents to a few dollars per month.

However, when you build a filter into an HVAC system, energy costs can increase with higher MERV filters if your fans are run by an EMC (electronically commuted motor). If your fans are run by a PSC (permanent split capacitor), you will not see a significant increase in energy costs. However, there will still be pressure drops for high MERV filters when they are loaded with dust.

Please note that this last point only applies to fibrous filters. Some machines powered by ActivePure do not use filters at all.

10. What Extras Does It Have?

This may be the least important question for most, but it is still a question to ask. Do you want a purifier with multiple layers of prefiltering and filtering? Do you want to be able to operate it from your smartphone? Do you want a sleek design and intuitive controls?

A Few Final Words

woman holding flowers indoors which introduces allergens into the air, which is reason to choose an ir purifier.

Now you know which questions to ask when choosing an air purifier. Go forth then and gather your answers like flowers into a beautiful bouquet. Then find a purifier that will get rid of the pollen shed by that bouquet.

If you still need help deciding, ActivePure’s experts will be happy to answer any additional questions you have. Their professional opinion will be a breath of fresh air on your quest for fresh air.

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