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Air Purifier and De-humidifier Buyer Guide |

Air Purifier Buyer Guide

Live in a pollution free environment at home. Get yourself an air purifier to remove impurities and allergens from the air you breathe. This guide will introduce you to the following points:

  • How to know when you need an air purifier
  • Functions of an air purifier
  • Types of air purifiers and the filters they use
  • Understanding CADR and knowing what CADR rating to look for
  • The different mounting styles of air purifiers
  • Features to keep in mind when selecting an air purifier

Air Purifier

Why do you need an Air Purifier?

You need an air purifier for the following reasons:

  • You're allergic to pollen and dust
  • You suffer from asthma and want to reduce the amount of triggers in a space
  • To reduce the percentage of allergens, bacteria and virus in a space
  • To remove smoke and odour from the environment and ensure healthy living

Dust particles, allergen and bacteria can be present in different shapes and sizes in the air. An air purifier helps catching all of these, thereby reducing the pollutants from the environment

. For comparison, here's a table charting the difference in size of various particles:

Particle Size (in microns)
Tobacco smoke 0.003 – 0.04
Bacteria 0.3 - 3
Fungi 0.5 - 5
Mould 2 - 20
Dust mite 10 - 40
Plant spores 10 - 70
Pet dander 0.3 – 100
Pollen 10 - 100

Types of Air Purifier

Wall-mounted Air Purifier


  • Wall-mounted air purifiers usually have higher capacities than floor-mounted models.
  • They're suitable for large rooms of 500 square feet and above.
  • However, you can also get lower capacity models if you don't want your air purifier to take up floor space.
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  • Floor-mounted air purifiers are much larger than portable models, but they can be moved around too.
  • They have a higher capacity and can serve medium size rooms of 300 to 500 square feet.

Portable Air Purifier


Ideal for placing on table tops, shelves and in cars.

Filter Types

Air purifiers are also further classified based on the filters they use. Here are a few types:


  • Catches tiny contaminants of not less than 0.3 microns.
  • Filters impurities such as pollen, mould, dust mite debris, bacteria and pet dander.

2. Electrostatic precipitator/ioniser

  • Lower upfront and maintenance cost
  • Removes very fine particles from the air. But the impurities may land on furniture and walls

3. Activated carbon

  • Usually used together with HEPA filters
  • Reduces odour, gas and smoke

4. UV light

  • Also known as germicidal filters
  • Kills viruses, bacteria, mould, and yeast

5. Pre-filter

  • Removes larger particle
  • Used for overall air purification

Area coverage for different types of heaters

  • 200-300 Square Feet: A portable air purifier is ideal for small spaces of 300 square feet and below.
  • 300-500 Square Feet: Medium size rooms of between 300 and 500 square feet will benefit from a floor-mounted air purifier.
  • 500 Square Feet and Above: Large rooms of more than 500 square feet will require bigger purifiers like large capacity floor-mounted models or wall-mounted purifiers.

Special Features

Dust sensor/air quality monitor

Dust sensor/air quality monitor

Your air purifier should be able to monitor dust levels and turn itself on when they hit a certain percentage.

Multiple fan speeds

Multiple fan speeds

This feature lets you control how quickly you want the air to be cycled. It also lets you control noise levels.

Filter replacement indicator

Filter replacement indicator

This makes it easy to know when a filter needs replacing.

Remote control

Remote control

You can adjust the air purifier from a distance with a remote control. This is especially useful for the elderly and the infirmed.



All air purifiers produce sounds but some are quieter than others. For comparison, normal breathing sounds are at 10 dB while a whisper is 30-40 dB.

Programmable timer

Programmable timer

A timer feature can let you set when you want the purifier to operate. This saves energy.

Turbo mode

Turbo mode

This feature comes in handy when you need to clean air quickly. The purifier is run at the maximum speed for a set period before slowing down.

Energy efficiency

Energy efficiency

Energy Star-rated air purifiers utilise electricity more efficiently. They can be 40 percent more efficient than non Energy Star-certified products.

Sleep mode

Sleep mode

With sleep mode on, the air purifier's fan speed is reduced and produces less noise.



Most air purifiers consume about 50W on a low setting and around 200W on high.

Understanding CADR, ACH, CFM

  • Getting the right air purifier size helps remove as many impurities as possible from a given space. Too-small sizes won't do a good job of purifying the air while too-large sizes will only translate to money wasted.
  • A high CADR or Clean Air Delivery Rate removes pollutants faster and ultimately, more effectively. To find a purifier with a CADR that's right for your room, multiple its square footage by .75. The resulting number is the minimum required CADR for that room. If you can't find the exact CADR required, round up the number.
  • Rooms with ceilings of 10 feet will benefit from purifiers with higher CADR. Add a 25 percent increase to the minimum CADR required.
  • An air purifier that produces more air changes per hour (ACH) keeps the air cleaner. Look for a model that changes air at least 4 times every hour.
  • Different cleaning settings have different CFM (cubic foot per minute) outputs, which is the amount of air a purifier can process. Ideally, a purifier should be able to clean about 160CFM in 200 sq ft of space (8 ft ceiling) with a light amount of smoke.

Quick tips for using an air purifier

  • For best results, leave the air purifier turned on continuously. You can reduce energy consumption by adjusting the cleaning speeds during different times of the day.
  • Place the air purifier at least a foot away from walls and furniture for better air circulation.

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