Choosing the right air filter can be a daunting task. Most people and households will be best off looking for flexibility in filter arrangements. An AllerAir system offers many options, with component filters that work individually and together, each replaceable separately. Their HEPA filter, for instance, will last up to five years. Their carbon filter, which removes odors and gasses, will likely be retired first-it lasts 18 months to 2 years. Austin Air's Healthmate line also addresses the complete air-cleaning spectrum, in a compact, wheel-around-the-house package.