Air Purifier Buying Guide ― 7 Important Questions to Answer

Cleaner indoor airIf you are looking to buy an air purifier for your home you can save a lot of time and money and make a much better choice by answering the 7 questions ahead.

You’ll learn what different kinds of air filters can and can’t do, why room size is so important, optional features and operating costs, why ACH and CADR rating matter, special considerations for asthma and allergy sufferers, and whether you should look for a HEPA, carbon, UV, ionizing or combination air purifier.

How to Choose an Air Purifier

It’s important to consider the size of the living space any room purifier is intended for. For example, an air cleaner used in a large living room will need to be bigger and more powerful than one for a small bedroom.

Also, what are the main forms of air pollution inside your house or apartment that you are most concerned about?

HEPA air filters are great for dust, pollen, pet dander and other particle pollution. However, airborne bacteria and viruses, cigarette smoke, pet odors, cooking smells and chemical gases like VOCs need specialized options.

Understanding certain air purification ratings and terms like CADR and ACH can help to judge an air purifiers performance. Different features, noise levels, replacement filter prices and other ongoing costs are also worth taking into account.

Buying a good air cleaning appliance is an investment in your family’s long-term health. Use these 7 questions ahead to help narrow down your choices and know exactly what to look for before you decide on the best air purifier for you.

1. What is an Air Purifier’s Purpose?

The main purpose of an air purifier is to filter the air in your home of microscopic airborne particles and other common forms of indoor air pollution.

The fewer pollutants floating in the air inside your house or apartment, the less chance you breathe them into your lungs where they can damage your health.

You may have special reasons to purchase an air purifier though, like a pollen, pet or dust mite allergy, being an asthmatic, having chemical sensitivities or living with an indoor smoker.

Consider what specific forms of air pollutants you need to deal with most and whether the model you are looking at is designed to deal with your particular air purification needs.

Even if you don’t suffer from allergies, asthma, or other obvious respiratory illnesses, breathing in mold spores, pet dander, pollen, dust mite waste, and other indoor allergy triggers can irritate your nasal passage and lungs, cause fatigue, lower your immunity and contribute to serious diseases.

2. How Do You Match an Air Purifier to Room Size?

Removing indoor allergensAn air purifier should be placed and used in the room that you and your family spend the most time in, like the living room. Many people who suffer from allergies or asthma also greatly benefit from extra air filtration in their bedroom.

Wherever you choose to position and operate your air cleaner, it’s important to match the size of the room with the air filtering power of the purifier in square feet.

First you need to know the size of the room. To calculate the square footage of any living area you simply multiply its length by its width.

So for instance, a lounge room that is 16 ft by 25 ft would be 400 sq ft. A smaller 10 ft by 20 ft bedroom would be 200 sq ft.

The majority of reputable air purifier companies will clearly display the recommended air cleaning coverage area in square feet on their website and Amazon. Consider it a red flag if any manufacturer does not provide this information.

What Size Air Purifier Do You Really Need?

While many room purifiers advertise a high ‘recommended coverage area’, this figure should be considered a maximum range so ideally look for coverage at least 25% above your room’s square footage.

As an example, a 400 sq ft living room would require an air purifier with 500 sq ft coverage at a minimum. With a 200 sq ft bedroom, go for at least a recommended 250 sq ft covered to filter dust mite contaminants and other bedroom allergens properly.

If you have pets, higher ceilings, mold or pollen problems, old carpets, degrading paint, lots of manufactured wood furniture or live in a high pollution area, then it’s best to require a sq ft coverage at least 50% more than your room size before you buy.

There’s an extra advantage with larger and higher quality air purifiers too ― they are still effective at lower and much quieter settings, making them ideal for bedrooms.

People who suffer from asthma or allergies need extra protection from poor air quality. If you are asthmatic or experience pollen or pet dander allergies, higher recommended room coverage area is important to look for.

However, a high CADR rating and ACH rate are even more beneficial metrics to consider when buying an air purifier. Let’s consider these 2 popular rating factors next.

3. What is the CADR Rating?

Better air qualityCADR stands for Clean Air Delivery Rate. It is a numeric rating system used to measure the effectiveness of home air purifiers at removing particle pollution from household air.

The CADR rating of an air cleaner shows the volume of filtered air produced in cubic feet per minute. It was developed by the Association of Home Appliance Manufacturers in the 1980s to standardize air purifier performance in a measurable metric.

A CADR rate can be applied to all types of air filtration technology, though you are most likely to find larger HEPA-based air filters advertising their CADR rating as they will naturally achieve a higher figure than smaller air purifiers.

If you are considering a CADR rated room purifier, then the higher rating the better. Under 100 is generally considered low, though could be okay for a small desktop purifier. 100 to 200 is more appropriate for smaller rooms, while above 200 is better for larger living spaces.

Air purifiers with the CADR rating over 300 will be a powerful air filter and highly beneficial for asthmatics and indoor allergy sufferers. You can find more specific details about how the rating is determined on this Wikipedia entry.

4. What is the ACH Rate?

The Air Changes per Hour rate (ACH) measures how many times an air purifier can effectively filter the amount of air in a given sq ft room per hour. ACH rate is a simple numeric scale, with 1 or 2 being low and 4 or above considered high.

Keep in mind it is also based on the recommended square foot coverage area of the air purifier being measured. So a model with 600 sq ft coverage and a 3X ACH rate would be expected to completely filter the air in a room up to 600 sq ft 3 times in an hour.

If indoor air pollutants are relatively equal throughout the house, this ACH rate would be higher in a smaller room but lower in a bigger one with more air to clean.

If you have asthma or regular allergies then look for a rate of 4 Air Changes per Hour or more to dramatically reduce indoor allergens and asthma triggers.

5. What Kind of Air Purifier Do You Need?

When choosing a particular model of air purifier to buy, there are 4 main technologies used in popular brands to consider:

HEPA Filters

Air purification buyers guideA High-Efficiency Particulate Air (HEPA) air cleaner will effectively filter airborne particles down to an extremely small 0.3 microns in any room it operates in.

HEPA filters work best for dust, pollen, pet dander, mold spores, cockroach and dust mite contaminants and other floating particle pollutants.

If this is the primary reason why you want to buy an air purifier, then a HEPA purifier is ideal. Make sure though that a ‘true HEPA’ filter is used and not the far less effective ‘HEPA-like’ alternatives.

Activated Carbon Filters

While HEPA filters a great for indoor particle pollution, they are usually ineffective for cigarette smoke, animal smells, cooking odors, or harmful VOCs from carpet, furniture and a surprising number of other household air pollutants.

For these gas, smoke and chemical-based contaminants, activated carbon filtration is the much better option.

Carbon filters are made from a special form of activated charcoal with millions of tiny pores that absorb odors, tobacco smoke, volatile organic compounds and other gaseous-based household air pollution.

Many high-quality room purifier models combine carbon filters with HEPA purification for synergistic air cleaning of both airborne particles and harmful gases.

Ultraviolet Air Purification

Specialized air cleaners, like this Germ Guardian bestseller, utilize safe UV-C light completely contained within the purifier, to destroy airborne viruses and bacteria.

UV filters are also extra protection against other floating biological contaminants like mold spores and pollen grains.

Like carbon filters, they are often combined with a true HEPA filter for multistage air purification.

Electrostatic and Ionizing Air Cleaners

Ionizing air purifiers work in a different way by emitting negatively charged ions. These ions attach to floating pollutants, forcing them to clump together and fall to the nearest surface.

Advanced multistage air purifiers may include an electrostatic precipitator with oppositely charged collection plates to capture microscopic pollutants missed by a HEPA filter.

Importantly, any room air filter with an electrostatic precipitator or negative ion generator should clearly state that it produces less ozone than the 0.05 ppm required by the FDA.

6. Do You Want Special Features and Optional Extras?

Portable air purifier technology has advanced greatly in recent years. Here are some optional extras and special features that you may want to look for when considering which model to buy.

Remote Control

Like your TV remote, this lets you control your room purifier from the couch or dining room table. In a recent innovation, this Blue Air HEPAsilent model can even be controlled by an app on your smartphone.

Programmable Timer

While it’s recommended to leave air purifiers running 24/7 for best results, this option lets you program the unit only run on a set schedule, such as during the daytime and switch off at night.

Adjustable Fan Speed

Large air purifiers often have multiple fan speeds, including a much quieter mode for bedrooms. If noise is a factor then this usually makes them far superior to cheap smaller models that often have only one noisier fan speed.

Service Indicator

HEPA and carbon filters need to be changed from time to time for best air cleaning results. An indicator light or warning message showing when a filter is losing effectiveness is a handy to have.

This feature may actually save you money if it shows a filter is lasting longer than the manufacturer’s recommended change interval and you can wait to replace it.

Air Pollution Sensor

Top range room purifiers may have a special sensor to detect higher levels of pollutants and adjust their fan speed and air purification accordingly.

This is particularly beneficial for homes where indoor air quality changes dramatically, such as due to indoor smoking, visiting pets or pollen season.

UV Germicidal Lamp

Filter airborne virusesMost effective for killing bacteria and viruses, safe UV-C lamps designed to kill germs can be found in some multistage air filtration purifiers.

This is a good feature to look for in your air purifier if you have children that regularly get colds or other sicknesses and spread them throughout your family.

Negative Ionizer

Some air purifiers also include a negative ion generator or electrostatic precipitator for an extra air cleaning method. Negative ions may also counteract fatigue from too many positive ions and some research shows they can improve your mood.

Importantly, any air purification device with an ionizer or electrostatic precipitator should clearly state that any ozone produced is well below the FDA’s safe level of 0.05 ppm.

Many people prefer to have an ionizer only as an adjustable setting that they can switch on or off to be extra safe.

Wheels and a Handle

Large air purifiers can be heavy. If you think you may want the appliance to be easily portable between rooms then this is a good feature to look out for.

7. What Other Factors Should You Consider Before Buying a Room Purifier?

You Still Need to Clean

Air filters are much more effective if there are less dust and other common sources of indoor air pollution already in your home.

Cleaning regularly with non-toxic cleaning products, combating dampness and mold, keeping pets away from living areas and reducing other indoor allergy triggers all help your air purifier to do its job better.

They Don’t Filter Everything

Some forms of gas-based pollution, like carbon monoxide and radon, are deadly and require monitoring for your family’s safety. Learn about these and more in 5 dangerous indoor air pollutants here but don’t rely solely on an air purifier to deal with them.

HEPA only filters are also ineffective for VOCs and other chemical gases. An activated carbon purifier can help but it’s best to minimize this hidden yet toxic form of household air pollution.

Consider Noise Levels

Check customer reviews for noisiness or decibel levels if the manufacturer lists them. Counterintuitively, small air purifiers are often noisier than larger ones as they have to work much harder to clean the air.

Most top range air purification systems have a quiet mode for sleeping so can be used in the bedroom overnight. Some even come with a ‘pink noise’ generator designed to help you sleep.

Filters Need Replacing

HEPA and activated carbon filters need to be replaced occasionally for maximum effectiveness. Replacement times vary, but periods between 1 year and 6 months are common, though check manufacturers instructions or the filter replacement indicator if your model has one.

There are Operating Costs

Check the retail price of the replacement filters of any room purifier you are considering and factor them into the overall cost over several years of air cleaning.

Also look for an energy efficiency rating to save on operating costs. This Alen Breathesmart purifier, for instance, states that it only uses the equivalent electricity to 105 W light bulb.

Check the Warranty

All good air purifiers should come with the manufacturer’s warranty. The longer it is, the more confident you can be that it will be purifying the air in your home for many years to come.

Choosing the Best Air Purifier for Your Home

I hope this detailed air purifier buying guide has given you a useful checklist of factors to consider before making a purchase.

A good air purifier can do wonders for indoor air quality in your home and make a significant difference to your family’s health and well-being, both in the short term and for years to come.

Now that you know how to choose an air purifier, look through some of these best sellers and their features here on Amazon and see if any of them would be the right option for your home.