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Will High-Efficiency Filters or High-MERV Filters Harm My HVAC System?

High-efficiency and high-MERV (Minimum Efficiency Reporting Value) rating filters seem beneficial because they filter out very small particulates, such as pollen, dander, and other allergens. Yet these types of filters have some negative consequences too. Here are some benefits and drawbacks of high-efficiency and high-MERV rating filters.

The Role of the Filter in HVAC

The primary purpose of a heating and air conditioning filter is to prevent dust and debris from clogging the unit. Many homeowners also purchase filters for their air quality enhancing properties, making them a must-have purchase for allergy sufferers. High-efficiency or high-MERV rating filters may capture more particulates, but their construction may not benefit the HVAC system. Filtering smaller particulates may lead to decreased airflow.

Do These Filters Harm HVAC Systems?

Most systems use either PSC (permanent split capacitor) or ECM (electronically commutated motors) technology. PSC motors have two settings: “on” and “off.” ECM motors are variable speed motors that adjust according to the needs of the environment and thermostat.

In most cases, high-efficiency filters (i.e., restrictive filters) won’t harm HVAC equipment, but they don’t offer as many benefits as a homeowner might believe. A PSC motor can only provide a certain level of air output, regardless of filter conditions. If the filter is too restrictive or too dirty, it will slightly reduce airflow through the system and into the home. An ECM motor, on the other hand, always tries to compensate for differences between its running capacity and the home environment. A dirty or restrictive filter may cause an ECM motor to use more energy to force more air through the system. Instead of saving energy, this type of reaction can significantly reduce HVAC efficiency.

How Different MERV Ratings Affect HVAC Systems

Some of the most common MERV ratings for high-efficiency filters range from 8-14. The higher the MERV rating, the more a filter can capture. Some filters may even capture certain viruses. Most systems expect a pressure drop of up to 0.5 inches, but high-MERV rating filters may cause a pressure drop higher than 0.18 inches, rendering the system even more inefficient.

To account for these pressure-related differences, talk to a professional HVAC technician about compensating for a high-efficiency or high-MERV filter. A trained professional can recommend accommodations to offset the airflow and pressure consequences of a high-efficiency filter and to keep the heating and air conditioning system running efficiently over time.

Choosing an Air Filter

The next time you purchase an air filter at a big box store or online, take a moment to look at the specifications. Look for the MERV rating and any information about air flow speeds. A thicker filter may not always provide better filtration results. A high industry rating, such as a MERV rating, may not always tell the entire story.

If you have any questions about what filter will improve efficiency, contact Palo Alto Plumbing for a recommendation.