Most people buying their first air purifier are surprised at the noise it makes in the home. Only a few are really quiet.
Despite the universal, and often false, “quiet" claim by air purifier manufacturers, “Noisy on the high speed” is by far the most frequent consumer complaint.
The real issue is not how loud a purifier is on high, but how much sound it makes while cleaning meaningful amounts of air. Several premium air purifiers are loud on high, but offer as many as six speeds for useful quiet air purification.
The Decibel (dB) scale measures noise in objective terms.
On the Decibel scale, each 10 points [dB(A)] added represents 10 times as much sound. For example; 70 dB(A), is not 17% louder, but ten times as loud as 60 dB(A). With many purifiers topping out in the low 70’s, louder than normal conversation, sound levels are a major consumer concern.
A few Decibel ratings;
Threshold of human hearing: 0 dB(A)
Quietest air purifier: 15 dB(A)
Soft whisper: 20 dB(A)
Good air purifier on low: 32 dB(A)
Ordinary air purifier on low: 36 dB(A)
Refrigerator: 50 dB(A)
Normal conversation: 60 dB(A)
Dishwasher running: 55-70 dB(A)
Typical air purifier on high: 66 dB(A)
Busy street traffic, loud air purifier: 70 dB(A )
Car interior: 75 dB(A)
Vacuum cleaner: 80 dB(A)
Common home stereo: 80 dB(A)
Lawn mower: 90 dB(A)
Rock concert: 110 dB(A)
The air purifier industry has no standards for noise levels. Only a few vendors voluntarily reveal actual decibel sound emissions.
Many people will find equally noisy machines are not equally distracting. This is because the combination of sounds is different, more harmonious.
The notion that a quieter air purifier produces less stress and improved health is confirmed by scientific studies. Prolonged exposure to noise levels above 70 dBA can cause hearing loss. Noise levels greater than 50 dB(A) can make quiet conversation impossible.
Most air purifiers have a fan to move air. Nobody has found a way to clean air without moving it. Moving air makes noise.
We are told to make a purchase based on the largest room size an air purifier can clean. Manufacturer’s room size recommendations are based on full time high speed operation. This is not acceptable to most users, who will turn the purifier down or off.
A bigger air purifier can clean the smaller room on lower speeds, often quietly. Many air purifier buyers make the mistake of saving money by selecting a less expensive purifier when the most powerful model in that same vendor's product line is maybe only $20 higher.
A smaller unit will have to run on high continuously, and most smaller air purifiers are noisy on high. A bigger air purifier can run for a few minutes on high, and then be turned down to a quiet level.
Noise levels in decibels are not useful without associated airflow data. If it isn't moving any air, who cares how “quiet" it is? Reviews should cite a noise level with a related Clean Air Delivery Rate (CADR) or airflow rate in cubic feet per minute (cfm). For example: 40dB(A)@212cfm is pretty quiet for the air being cleaned.
Well engineered backward curved fan blades and sealed ball bearing motors are less noisy. They cost more.
Noise can also develop when bearings or bushings wear out on cheaper motors, allowing side play of the fan shaft. When slack allows fan blades to rub housings, vibrations increase.
Consumers can avoid “quiet air purifier” disappointment by demanding true sound data from manufacturers, and installing a larger model than builders recommend for their room.
The author, Ed Sherbenou, has experience with air purifiers dating back to 1977. His air purifier reviews leave no stone unturned, and few questions unanswered. Ed is an opinionated critic, not a seller, of air purifiers. Indoor air quality and air purifier technical details, often missing from seller's websites, can be found at: http://www.air-purifier-power.com