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Quietest AP 1200 Yayimages 4889088 noise

Best Quiet Air Purifiers 2021-novel system to half the noise

Noisy air purifiers are annoying and a health hazard as people switch them down because of the noise and then no longer have adequate air purification. I should know because I made the same mistake. You can avoid this by picking quietest air purifier on the market.

The quietest air purifiers are the Coway 400S and the Coway 300S this is due to their dual filter design. Dual filters give a large surface area so the air flow can be relatively slow and still purify a large volume of air. They have the highest airflow per decibel of any air purifier or the market, under 52db.

These air purifiers can be used in a new system, which I outline below, to give you quieter air purification than you could get without using the system.

We are fortunate that we live in an age when air cleaning to improve indoor air quality is so good that we can reduce particle count by 80-90%. However, to be this effective we need to choose the right air purifier and use good technique.

All air purifiers need to be chosen so they have a clean air delivery rate (CADR) that is adequate for the room. You can estimate the CADR rating that you will need for your room from the following EPA table-

Quietest air purifier-

This table assumes ceilings 8 feet high, if yours are higher or you would prefer to use a calculator you can find one on this page.

The problem is that most manufacturers only give the CADR at the highest fan speed. So like most potential customers, you can only match your needed CADR, to the maximum CADR of an air purifier. So you are likely to buy an air purifier with a maximum CADR only slightly higher than you need. What else are you to do?

Most air purifiers are intolerably noisy on their highest setting. So you will naturally switch the fan speed down to the next level. This is likely not to be enough for good air quality in your room as you sized the air purifier to your room using the maximum air flow.

Unless you actually measure the particle count at this lower air flow rate you may not realise that the airborne particle reduction is only 50%. So you are now breathing in 30% more airborne pollutants than the EPA’s recommendation of an at least 80% reduction. Without realizing it this higher particle count is likely to gradually degrade your health as there is overwhelming evidence that particle count damages human health even at low levels. For further information please see this article.

This must be happening in millions of US homes each day, reviews often mention how quiet the air purifier is on a lower setting. So people are often turning them down.

So having a quiet air purifier with a high flow rate means that there will be no need to turn it down onto an ineffective setting which is important from a health point of view.

To avoid this problem-

First Find a Noise Level That You Are Happy With

Sound levels for some common sounds within the noise range that air purifiers make-

Type of SoundSound Intensity (db)
Vacuum cleaner at 10ft75
Conversation in office/restaurant at 3ft60
Quiet Suburb, Conversation at home, Large business office, Dishwasher next room50
Bird calls44
Library37
Quiet rural area35
Bedroom at night30
Whisper20
Silence0
Table compiled from various sources including-source, source

Please bear in mind that the decibel scale is exponential so relative to a 30db sound a 40db sound will sound twice as loud, a 50db sound four times as loud and a 60db sound 8 times as loud as a sound of 30db.

Human hearing is not uniform we do not hear low frequencies so well but hear higher frequencies like the cry of a baby more strongly. So the frequency of the sound has to be taken into consideration. Air purifiers emit higher pitched white noise. So they can be more noticeable in terms of pitch. However, as it is a constant noise, it is easier to tune out as a background noise.

Also, larger air purifiers tend to emit lower tones which are easier on the ear. This is much as larger string instruments, eg a double base emit lower frequency sounds, whereas smaller string instruments such as a violin emit higher frequency sounds. Similarly, a larger air purifier will tend to emit lower frequency sounds which are not so noticeable to human hearing. The Coway 400S and 300S are both medium to large air purifiers and so emit lower frequency sounds, making any sound they produce easier on the ears.

My experience with air purifiers is that anything above 50db during the day and 40db when sleeping is certainly too much, in general I think that less than 35db is probably a better target for sleep.

A Method for finding an acceptable noise level for you

You will need 2 mobile phones one as a noise generator and one for measuring noise level.

  • Put one phone where you intend the air purifier to be and get it to generate white or pink noise at a fairly loud level.
  • Put the other phone 6 feet away from the air purifier recording the sound level (for some reason air purifiers seem to have their noise levels measured from about 6 feet away).
  • Sit or stand where you will be in the room most of the time and see if the noise is too loud. If it is then decrease it until you think that it is about right. If it is quieter than would suit you increase the volume.
  • When you think the noise is about right, read a book or surf the internet for 10 minutes and see if the noise from the phone is too loud longterm when you try to work.
  • If the noise is too loud decrease it slightly and repeat the previous step. Conversely, if it is too quiet, increase the noise level and repeat the previous step.
  • Note the sound intensity on the mobile phone recording the sound, this is your acceptable noise level.

a) Awake-ideally choose your noise level using method above or use a maximum of 50db

Alternatively if you do not have the time or inclination to use the above method, you could accept my ballpark estimate of a maximum comfortable noise level from an air purifier when you are awake of 50db or less.

b) Sleeping-ideally choose your noise level using method above or use a maximum of 35db

Similarly rather than measure your own sound tolerance, which would be best, you may simply accept my ballpark estimate for sleep of a maximum sound level of 35 db or less.

You now know your acceptable noise level or have a noise level to aim for which is a great step forward. You also know the size of your room and so what clean air delivery rate you need, and so you can choose an air purifier that will produce this clean air delivery rate at a noise below your acceptable noise threshold. Then you can be sure the air purifier will not be too loud for you.

Air Purifier Basic Specifications

Before choosing the best air purifier there are some basic specifications-

  1. Excellent filtration of airborne particles, so you should buy a HEPA air purifier, with a true HEPA filter avoid those with “HEPA like” or “HEPA style”…. filters. This air filter removes particles such as airborne allergens, pet hair, pet dander, dust particles, mold spores, dust mite and even smoke particles with a very high efficiency. They are thought to have serious health effects. Some filters are specified to deal with ultrafine particles, my choices the Coway 300S and Coway 400S both deal with ultrafine particles down to 10nm in diameter.
  2. Ideally it should also have a carbon filter. The activated carbon removes airborne chemicals including those causing odors.

For additional information please see this article on how air purifiers work.

Of course filter replacement will be necessary and the expense of this can be very different from one air purifier to another. These expenses are outlined below for the air purifiers chosen.

UV light is not essential and indeed, many of the top air purifiers do not have it. It is less effective in HEPA filter because the air passes by the UV light so quickly that there is little time for any micro-organism in the air to be irradiated and destroyed.

Other air purifiers without HEPA filters are not recommended, as they have not been found to be as effective as HEPA filters.

The Best Quietest Air Purifiers

The choices here represent the best choices of air purifiers from all established manufactures on the market who would give me the noise levels at their machine’s various CADR ratings. This information was needed so that I did not recommend an air purifier that is too noisy for you.

We also need a smart air purifier, for health reasons an air purifier needs to come on 30 minutes at least before you step into the room as explained here. Thus, a schedule for it switching on and off needs to be programmable. So only those air purifiers with smart control or those that could be made smart with a smart plug were considered.

The criteria for choosing the air purifiers for consideration were all backed by health considerations as outlined in this diagram-

Air purifier selection

This narrows down the list dramatically in a logical way based on health criteria.

You will be used to seeing reviews that offer the “best 8 quiet air purifiers” in reality, there are not 8 roughly equivalent quiet air purifiers. It will not surprise you that in most categories, as in life or an Olympic race, there is almost always a clear winner. Here it is a surprise that there are 2 joint winners. Compared to these 2 air purifiers, on average other air purifiers on the market are twice as loud, for an equivalent air flow, so it is not even a close contest!

Incidentally, the “best 8 quiet air purifiers” reviews almost always contain an air purifier with a hidden problem that the review does not point out, and which logically would lead to a considerably higher particle count and so presumably faster deterioration in the health of those buying the air purifier. Some of the choices are simply wrong on the data available.

Anyway here are my choices for the best quiet air purifier after some research and obtaining data from the manufacturers which is not on the website or in the manual-

Coway 400S

This air purifier has an extremely highly specified HEPA filter which deals with ultrafine particles. It is so quiet that it will even purify the air in a room of 300 sq ft at a noise level of 28db, which would feel about half as loud as my maximum sound level for sleep, so this is a very quiet purifier! This would also make the Coway 400S the ideal bedroom air purifier.

Specifications

Pros
  • Large room capability supreme-642 sq ft at a noise level of 51db
  • HEPA filter also specified to remove most ultrafine particles
  • Smart control
Cons
  • Not the cheapest air purifier but also not the most expensive
Best quiet ari purifiers Coway 400S
Coway 400S published with the kind permission of Coway Airmega

Specifications

Filters
HEPA filterHEPA specified to remove 99.8% of ultrafine particles down to a size of 0.01um
Carbon filter amount of carbon (lb)1.5 lb so more than most other air purifiers
Filter Change HEPA (Particles)12 months
Filter Change Carbon (Chemicals)12 months
Airflow
CADR at =<50db (CADR on Maximum)293 cfm
Maximum Room Size (Noise less than 50db*)450 sq ft
Maximum Room Size (On noisiest setting)640 sq ft

Smart ControlYes phone app/Alexa:/Google Home

Power66 W
Weight24.7 lbs
Dimensions “H x “W x D”22.8 x 14.8 x 14.8

Annual Running Cost Electricity ($)$40
Annual Running Cost Filters ($)$120
Total Annual Running Cost ($)$160

All the above are approximate and assume running the air purifier for 12 hours per day on the highest setting that keeps the noise below 35db.

*Most people will not wish to have the air purifier on a setting louder than about 35db for sleeping in a bedroom-you may wish to have a quieter setting than 35db this is just a ballpark estimate for most people. On the other hand, if your room layout allows you to be much further than 6 feet from the air purifier you may find the noise this air purifier makes at top speed is alright. The calculations for room size assume that you have 8 foot ceilings and 5 air changes per hour.

Never run an air purifier on auto mode using the inbuilt sensor. These cannot detect ultrafine particles which are damaging to human health, please see this article.

Its appearance is generally pleasing and it comes in black and white. The holes in the grill add some black to the white and soften it. The top is black and as the air purifier is not very tall you will be looking down on a black square in your room.

I sometimes think that there should also be a midrange color option, ideally a light grey like the iQair HealthPro Plus or a matt metallic slightly reflective coating which can reflect other colours in the room. In this way the air purifier would blend in with your decor, not stick out. Both white and black add contrast in a room of intermediate colors, and so the eye is naturally drawn to the air purifier.

Coway 300S

The smaller partner to the Coway 400S. The second highest airflow per decibel on the market in the reasonable noise range. There is one air purifier that has a higher airflow per decibel but only when it is on its highest setting and making so much noise that it would be impossible to be in the room with it for long.

Pros
  • Large room capability excellent purifier-545 sq ft at a noise level of 50db
  • HEPA filter also specified to remove most ultrafine particles
  • Smart control
Cons
  • Not the cheapest air purifier but also not the most expensive
Best quiet air purifiers Coway 300S
Coway 300S published with the kind permission of Coway Airmega

Specifications

Filters
HEPA filterHEPA specified to remove 99.8% of ultrafine particles down to a size of 0.01um
Carbon filter amount of carbon (lb)1.5 lb so more than most other air purifiers
Filter Change HEPA (Particles)12 months
Filter Change Carbon (Chemicals)12 months
Airflow
CADR at =<50db (CADR on Maximum)354 cfm (354 cfm)
Maximum Room Size (Noise less than 50db*)545 sq ft
Maximum Room Size (On noisiest setting)545 sq ft

Smart ControlYes phone app

Power57 W
Weight21.4 lbs
Dimensions “H x “W x D”21.2 x 13.6 x 13.6

Annual Running Cost Electricity ($)$40
Annual Running Cost Filters ($)$120
Total Annual Running Cost ($)$160

All the above are approximate and assume running the air purifier for 12 hours per day on the highest setting that keeps the noise below 35db.

*Most people will not wish to have the air purifier on a setting louder than about 35db for sleeping in a bedroom-you may wish to have a quieter setting than 35db this is just a ballpark estimate for most people. On the other hand, if your room layout allows you to be much further than 6 feet from the air purifier you may find the noise this air purifier makes at top speed is alright. The calculations for room size assume that you have 8 foot ceilings and 5 air changes per hour.

Never run an air purifier on auto mode using the inbuilt sensor. These cannot detect ultrafine particles which are damaging to human health, please see this article.

Why Both Coways?-an example of a new system

The noise levels at various fan speeds makes each one more suitable for specific situations.

The Coway 300S is the ultimate air purifier for bedrooms it will purify the air in a bedroom up to 370 sq ft at a noise level of 32 db whereas the Coway 400S would be twice as noisy for a room of this size at 43db. Most other air purifiers on the market would be twice as noisy again. So for a bedroom of this size, the Coway 300S makes about a quarter of the noise of the average air purifier.

Coway Room Size 1200 1

The diagram does not go below 28db as this sound level is virtually inaudible in a room, and should be quiet enough for anyone.

This novel system that I have developed of picking individual speeds for particular room sizes ensures the quietest choice of air purifier for a particular room. It works well for these 2 Coway models, one of these 2 air purifiers depending on room size will give you the quietest possible air purification for your room.

Winix AM90-more cost effective option for rooms up to 194 sq ft

This is the replacement for the Winix 5500 air cleaner and has the advantage of smart Wi-Fi control. For sleeping, this air purifier can be only be recommended for rooms up to 145 sq ft as the noise level to serve a room of this size is 36db.

Pros
  • Less than half the price of the Coway S400 and S300 and suitable for rooms up to 194 sq ft whilst keeping the noise level below 50db
  • WIFI control-very important for mold as explained above
  • Running costs low $70 per year
Cons
  • Would only be suitable for a bedroom of 145 sq ft
best air purifer for mold Winix AM90
Filters
HEPA filterHEPA 13 filter
Carbon filter amount of carbonSmall amount of carbon incorporated into main filter 0.1 lb
Filter Change HEPA (Particles)12 months
Filter Change Carbon (Chemicals)3 months
Airflow
CADR at =<50db (CADR on Maximum)126 cfm (234 cfm)
Maximum Room Size (Noise less than 50db*)194 sq ft
Maximum Room Size (On noisiest setting)360 sq ft

Smart ControlSmart Phone App

Power65 W
Weight15.8 lb
Dimensions “H x “W x D”23.5 x 8.7 x 15.1 inches

Annual Running Cost Electricity$40
Annual Running Cost Filters$80
Total Annual Running Cost$120

All the above are approximate and assume running the air purifier for 12 hours per day on the highest setting that keeps the noise below 35db.

*Most people will not wish to have the air purifier on a setting louder than about 35db for sleeping in a bedroom-you may wish to have a quieter setting than 35db this is just a ballpark estimate for most people. On the other hand, if your room layout allows you to be much further than 6 feet from the air purifier you may find the noise this air purifier makes at top speed is alright. The calculations for room size assume that you have 8 foot ceilings and 5 air changes per hour.

Never run an air purifier on auto mode using the inbuilt sensor. These cannot detect ultrafine particles which are damaging to human health, please see this article.

When would a quiet air purifier come in handy?

A quiet air purifier is good to have at all times but especially for-

  • Sleeping
  • Babies
  • People when ill
  • People under stress
  • Video conferencing
  • Sound recording

What rooms need quiet HEPA air purifiers?

If you are going to buy an air purifier you might as well buy a quiet one. The rooms that need one are those that you spend most of the day in, so a kitchen and or study/living room and for night time an air purifier in your bedroom. The idea is to breathe purified air for as many hours as possible during the day.

How to control your quiet HEPA air purifier?

As a general rule it is best to control your air purifier by buying an air quality meter and aiming for the greatest reduction in particle count or pollution that you can achieve. Comparing the particle count or air pollution before switching the air purifier on with that after it has been on for an hour, the EPA recommends an at least 80% reduction. What ever you do, do not let your air purifier control itself, the 7 reasons for this are given here.

Conclusion

The quietest air purifier on the market per unit air flow is the Coway 400S, which is a very quiet HEPA air purifier. The only other air purifier that comes close is the Coway 300S. For some room sizes and sound tolerances, the Coway 300S will be the best choice, please see the diagram above.

Both of these machines have an excellent filtration system which have specifications beyond the true HEPA standard and will effectively reduce airborne particles including most ultrafine particles. So quite apart from being the quietest air purifiers on the market they produce the second best specified air quality on the market.

Related Questions

See Also

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