The MERV (minimum efficiency reporting value) rating of a filter is a reference number describing its efficiency at removing airborne particles from the air inside your home. MERV numbers range from 1 to 16. The higher the number, the smaller the particles the filter will remove. For consumers, MERV numbers serve as a helpful guide for comparing the performance of different filters.
Inexpensive, disposable fiberglass filters are rated in the MERV range of 1 to 4. These remove particles of dust, pollen and fibers larger than 10 microns. At the high end of the spectrum are filters in the 15 to 16 range. Utilized mainly in medical or high-tech environments, these filters remove particles as small as 0.30 microns and are effective against airborne bacteria and other organic contaminants.
For household HVAC systems, the American Society of Heating, Refrigeration and Air Conditioning Engineers recommends a MERV of 6 or above. These are pleated filters capable of removing all dust and most allergens including mold spores. Residences with sensitive individuals might choose a filter rated up to 12 for superior filtration. Filters rated higher than 12 restrict airflow excessively.
For optimum air conditioner efficiency, filter rating must be balanced against system airflow. The higher the rating, the more restrictive the filter and the more it decreases airflow. Air conditioners are engineered for greatest efficiency when airflow is within the design range. Low airflow will result in less cooling and lower comfort level. The air conditioning compressor may run longer, struggling to meet cooling demands with less air. This causes higher electricity consumption and may shorten component life.
Conversely, filters with low ratings that allow too much airflow can cause buildup of dust in the system. Air passing over system components produces condensation. Dirt in insufficiently filtered air builds up on dam evaporator coils and elsewhere in the ducts, producing an environment that supports mold and bacteria.
For more information on improving HVAC efficiency, contact the pros at Stack Heating & Cooling. We’ve been helping homeowners in the Cleveland area since 1976.
Our goal is to help educate our customers about energy and home comfort issues (specific to HVAC systems). For more information about MERV numbers and other HVAC topics, download our free Home Comfort Resource guide.