Air purifiers are available in a variety of shapes, sizes and functions. Some remove allergens alone while others remove allergens, pollutants and odors, as well. We've scoured the internet and found the top eight air purifier units based on customer reviews and price.

How to Buy an Air Purifier

All air purifiers (http://www.dealhack.com/archives/2009/04/save_extra_25_off_hunter_air_p.html) are not created equally. Smaller units are best for small areas while large units are best for bigger areas. The first thing to look for is the number of sq ft the unit will clean. Also, make sure the unit will remove what needs to be removed.

Filter types are very important to take into consideration. HEPA air filters remove the big particles including dust and pollen as well as the small stuff like dander, mold and dust mites. All filters require replacement over time; make sure to purchase a unit that uses affordable filters.

Bacteria and viruses are not removed by most run-of-the-mill air purifiers. They must include a UV light in order to remove bacteria and viruses successfully.

Top Eight Air Purifiers (http://www.dealhack.com/archives/2010/04/save_up_to_50_off_holmes_air_p.html) Based on Customer Reviews

We scoured the internet looking for the best air purifiers based on customer reviews. We will share the specific pros and cons for each model when possible. Each model discussed here received at least 4.5 stars of a possible 5 star rating.

Alen A350: Features, performance and affordability in this wall mountable unit by Alen. This model removes 98% of particles and allergens from the air and is recommended for rooms up to 800 sq ft. Replacement HEPA filters are the most affordable with this unit compared to others. This unit runs around $400.

IQAir HealthPro Plus: Swedish engineering that packs a punch against airborne particles and odor. Pollen, dust mites, pet dander and mold can't linger with this air purifier on the job. This brand is an education partner with the American Lung Association and has been promoted on the television show "Extreme Makeover Home Edition." This unit is one of the more expensive on the market, running around $900.

Alen T300: This slim, sleek unit is recommended for 300 sq ft rooms, and removes 93% of particles from the air. The outward appearance is very contemporary and stylish. It uses HEPA filters and features an ionizer to produce negative ions, which have been shown to produce a feeling of well being. The UV lamp removes a percentage of bacterial contaminants. This unit sells for about $300.

Alen Paralda: This unit is named after Paralda, the elemental king of air. It removes 99% of impurities from rooms up to 400 sq ft. The Paralda also comes with a UV light that kills airborne viruses and bacteria. The design of this unit allows easy filter replacement with no tools required: simply lift the cover and replace the air filter. This unit sells for about $499.

IQAir HealthPro: This unit removes 99% of airborne particles in rooms up to 900 sq ft. The IQAir HealthPro does not eliminate or remove odor like the IQAir HealthPro Plus mentioned previously. You can, however, purchase a V-5 Cell gas and odor filter and turn the IQAir HealthPro into a HealthPro Plus. The IQAir HealthPro retails for about $749.

Alen A375UV Multi-Gas Air Purifier: Remove 98% of airborne particles and freshen the air in one fell swoop. This unit takes care of allergens, smoke, mold, bacteria, viruses and heavy pollutants like wildfire ash, chemical vapors and highway pollutants. The A375UV is wall mountable and features a remote control. This unit retails for around $600.

BlueAir 603: Whisper quiet operation is great for the bedroom or office. This unit offers one of the highest CADR (clean air delivery ratings). It removes 98% of indoor pollutants and is recommended for rooms about 640 sq ft. The BlueAir 603 doesn’t create annoying drafts; it pulls dirty air through the sides, front, back and bottom. This unit comes with an incredible 10 year warranty and costs about $700.

AllerAir 6000 Exec: This hefty unit is designed to work in rooms up to 1,800 sq ft. It removes airborne particles, chemicals, odors and fumes with ease. Available in three colors; black, sandstone or white, and runs around $700.