Home Air Filter Ratings Every Homeowner Needs To Know
Home air filter ratings encompass more than the familiar minimum efficiency reporting value ratings. MERV groups filters according to their efficiency at removing particulates of a specific size. The higher the MERV rating, the more efficient a filter is at maintaining air quality. But other parameters are also useful in evaluating the efficiency of an HVAC filter. These specifications affect factors such as airflow and filter service life. Here are some of those other air filter ratings:
- Pressure drop measures the decrease in system airflow caused by a clean filter, compared with no filter. The higher the filter resistance, the greater the pressure drop. A high pressure-drop rating means reduced airflow and increased electricity consumption by the blower fan to push air through the filter. Pressure drop increases as a filter becomes dirtier. Low pressure drop is directly related to increased energy efficiency and comfort.
- Dust spot efficiency measures a filter’s ability to remove large particles of dust. It expresses the percentage of a measured amount of test dust trapped by a filter at a certain velocity. The higher the dust-spot percentage, the more efficient the filter. Medical grade HEPA filters have dust spot efficiencies of more than 98 percent.
- The dust-holding capacity of a filter is determined by weighing the total amount of dust a filter can hold before it becomes completely obstructed. Dust holding is expressed in grams of dust. It’s often used as one parameter to calculate the length of time between filter changes.
- Initial and sustained efficiency figures compare the performance of a new filter versus its performance over time. Some filters don’t reach full efficiency until after they have been installed for some time and have acquired a certain amount of trapped dust or dirt. The best quality filters have both high initial and sustained efficiency ratings.