Now that you understand the different types of air filtration your first step is to identify what contaminants you are trying to remove. By having an idea of what you want to remove you can choose the most effective air filter to do so. For example, if you are a cigarette smoker a single HEPA filter will not be sufficient. A carbon activated filter will be more effective in removing the odors. If you are more interested in removing allergens such as dust, bacteria, pet dander, and mold it would be recommended to purchase a purifier with a HEPA filter because these are more effective in removing larger particulates.