Skip to Content

Does Your Air Filter Always Look Dirty?


A simple dirty air filter can cause a multiplicity of malfunctions in your cooling and heating system.

The typical residential HVAC system pushes over one thousand cubic feet of air through the filter every minute itandrsquo;s operating. Changing the air filter regularlyandmdash;ideally every month, especially during air conditioning seasonandmdash;helps prevent issues like substandard cooling and heating performance, high operating costs, poor indoor air quality and shortened component life. But what if your filter seems to need replacement before the typical service interval?

Here are some common reasons why a dirty air filter gets that way sooner than it ought to.


Airborne fur shed by dogs and cats inevitably gets pulled into the HVAC return vents and clogs the system filter. Brushing certain breeds more often may help and vacuuming regularly can reduce filter-clogging fur before it gets into the HVAC system.


If your thermostat fan setting is “Onandrdquo; instead of “Auto,” the system is pulling air through the filter all day and night and may overload it with particulates. Choosing the “Autoandrdquo; fan setting turns the fan off when the system cycles off and reduces filter accumulation of dust and dirt.


Leaks in return ductwork may be pulling dusty, dirty air from unconditioned zones into the system such as the attic or crawl space, adding to the filter load. Our qualified technician can inspect and pressure-test ducts to determine the extent of leakage and then suggest sealing options.


High-efficiency filters with MERV (Minimum Efficiency Rating Value) above 13 are generally not appropriate for standard residential systems that haven't been altered for this specific use. The filter media clogs much sooner and requires replacement more often to maintain sufficient airflow. For most home applications, pleated filters with a MERV rating between 8 and 12 usually provide a good balance between filtration performance and optimum airflow over a standard replacement interval.

Are you noticing a dirty air filter even before it's time for the regularly-scheduled replacement? Contact Valley Heating, Cooling, Electrical and Solar for a professional opinion.

Our goal is to help educate our customers in the South Bay Peninsula and Santa Cruz areas of California about energy and home comfort issues (specific to HVAC systems).

Share To: