HEPA Quiet Air Purifiers
If you have severe allergies and noise is an issue, then your best bet is to use one of the reasonably quiet air purifiers that use a HEPA filter, such as the Blueair air cleaners.
Noise levels from the Blueair register at just 32 dBa, which is comparable to a soft whisper when on low. When on high, this air purifier still only registers at 64 dBa, which is about as loud as a refrigerator.
The IQAir HealthPro air purifier, which has been found to be the best performing air purifier in various studies, registers at 44 dBa when on lower speeds. This is also about as loud as a refrigerator. However, when on high speed setting, it registers at 72 dBa, which is about as loud as a dishwasher.
UV Silent Air Purifiers
The only completely silent air purifier system is a UV or ultraviolet air purifier. These use both carbon and HEPA together with UV light to clean all toxins from the air. These systems work by killing germs as they pass through air ducts, where the system is normally installed. Consequently, you will only have to put up with the sound of your air system to get the benefits of UV.
Not so Quiet Air Purifiers with Air Filters
Among the not so quiet air purifiers are the portable units that use old-fashioned air filters and are available at discount stores for about $70. These air filters register at 70 dBa when on, which is about the same as the IQ Air HealthPro when it is set on high speed. You will likely need one of these air purifiers for each room in order to eliminate dust, pet dander and common allergens.
Ionic Silent Air Purifiers
Ionizing air purifiers typically do not have running motors, which makes them virtually silent. They work by emitting negatively charged ions into the air, which then bond to positively charged smoke and odor molecules. The combined weight of the bonded particles makes them too heavy to stay suspended in the air so they drop down to the collection plate at the base of the unit.
There is some debate as to whether these really do make a long-term difference as they do not remove the particles from the room or secure them for removal by entrapment within a filter.
Quiet Low Ozone Air Purifiers
Low-ozone air purifiers clean up the air by oxidizing the pollutants and they are often combined with ionizing systems. The quietest ozone ionizing air purifier available at present measures around 30 dBa on low and 51 dBa on high setting
If any of these air purifiers are still too noisy for you, or if you are looking for something lower tech, there are other options available.
Changing the air filters on your air conditioning and heating system once a month can help in reducing dust, pet dander and allergens by as much as 50%. The filters are silent, although you will have to put up with the noise of your HVAC system.
Plants as Quiet Air Purifiers
Living plants work as completely natural quiet air purifiers and are capable of removing nasty stuff in the air that nothing else can.
Living plants naturally process nasties such as carbon monoxide, benzene and formaldehyde. Plants such as Pothos and English Ivies are particularly good filters, are inexpensive and thrive on neglect and low light conditions.