Sizing Your Room and the Right Size Air Purifier
The size of the room is a significant factor when choosing an air purifier because in order to properly clean the air in a room, you will need to exchange the air in the room several times each hour. The reason for this is that initially the air will have a certain pollution level depending on your external environment and activity inside the area you are planning to clean and maintain. In the beginning the air changes will be necessary to reduce the pollution level until it is reduced by around 80%. After this the continuation of the air purifier will be to maintain the cleanliness of the air.

The more efficient an air purifier is with each pass the less air changes that will be needed to clean and maintain the air quality. Factors affecting how much you will need to clean the room would be the construction of the room as far as how much infiltration of pollution would be allowed to enter the room each hour. Also, how much activity is there in the room as far as doors opening and closing, people walking around, etc. This activity will stir up all the dust and particulates that has settled on the floors, furniture, and walls. Normally, you will look for a range of 2 to 8 air exchanges an hour with 2 air exchanges only being acceptable with the most efficient of the Hepa air purifiers. When cleaning the air for gases, odors, and chemicals it will be better to run the air purifier at a lower speed so the gas molecules will have more contact time with the activated carbon. This would also be true for units utilizing UV light to sterilize the particulates.

Where are you Going to Place the Air Purifier in your Room?
The placement in the room is important when you consider your air purifier choices. We recommend for bedrooms a quieter air purifier with less air exchanges during the night, than a family or living room where there will be more traffic and faster re-polluting of the air. Placement of the air purifier in the room will always be best if it is in the middle of the room. However, since particulates and gases will through diffusion maintain an equal distance between one another, as the particle count is reduced as the air purifier cleans, the room, the remaining particulates will spread out to maintain this equal distance. As they move across the room, they will eventually be drawn into the vacuum that is created by the air purifier’s fan. Therefore, placement of an air purifier on the sides or ends of a room will be able to filter the particles on the opposite side of the room.

Noise Level in Air Purifiers.
Noise level is a personal choice because some people do not mind, or even welcome a background white noise, while some people cannot stand any fan noise whatsoever. Also, when someone is purchasing an air purifier for a bedroom, they are usually looking not only for a quiet air purifier but also a smooth running machine that will not have an inconsistent pitch and noise level. What is helpful is not to make a purchasing decision solely based on the area size a specific air purifier can clean. The reason being a unit that can clean 800 square feet will still do an excellent job in a 200 square foot room with one important additional benefit. Because of the larger capacity air purifier, you will be able to properly clean the smaller room on the low or medium speeds, which are almost always significantly quieter on the larger Hepa air purifiers. If someone purchases an air purifier that is tight in its sizing capacity they will find they need to run the unit on high most of the time, and even the smaller air purifiers are noisy on the high speed. The only reason someone should not consider a larger air purifier is because of the physical size being too large for the room.

A perfect choice for a quiet air purifier for bedroom use is the Blueair 501 and 402. For a small bedroom and for portability consider the Hamilton Beach series.

Automatic Monitoring of Pollution Levels in a Room
There are some air purifiers which have an infrared detector that will monitor the amount of particulates in its vision. Initially, when turning on the air purifier, it will automatically run itself on the high speed, because the particle count will usually be high. As the particles in the detector’s vision are reduced, it will turn itself down to the medium speed and eventually to the lower speed. The idea in theory is excellent but since the area being measured is so small, the accuracy of this automatic monitoring device is in reality pretty minimal. A separate particulate monitor is recommended.

The Hamilton Beach Air Purifiers have this monitoring system.

Efficiency Level of your Air Purifier
Two critical things to consider when measuring how effective an air purifier is at performing, is the amount of air that it can clean each hour and what percentage of the pollution does it remove from the air that is circulating through it. This second factor is called the efficiency. For example, if the particle count per cubic foot of air going into the air purifier is 1,000,000 particles and the particle count of the air coming out after it has passed through the filters is 300, than the efficiency of the air purifier would be 99.97%. Therefore, you can see how the efficiency of the machine is important since a machine that is only 60% efficient would allow 400,000 particles to go back into the room.

The efficiency is important because there are many air purifiers on the market that have a Hepa filter but their relative efficiency is undocumented. This only means that the filter has been tested to remove 99.97% of all of the particulates that are 0.3 of a micron in size or larger. However, this is when all of the particles in the air contact the Hepa filter and none of the air is able to bypass the filter itself. Once you take the Hepa filter and install it in the air purifier other variable are involved. As the air is drawn into the air purifier, some of the air can bypass the filter media depending on the way the filter is housed inside of the air purifier. As much as 40 or 50 percent of the air can pass by the filter media in some Hepa filter based air purifiers resulting in poor performance.