Air Filter Always Dirty? Reasons Why

It’s normal to have a dirty air filter in your HVAC system every month or so. The entire air volume inside your house—including all the dust, dirt, lint and other particulates floating around in it—circulates through the filter multiple times each day. The filter should be checked and replaced every month during the cooling season and every month or two during heating season. A dirty air filter obstructs airflow, which in turns degrades system energy efficiency as well as cooling/heating performance.

But what if your filter always needs replacement sooner than that “normal” interval? If your filter’s getting excessively dirty before it ought to be, it could indicate one of the following issues:

Fan running non-stop.

The thermostat fan setting offers two selections: “On” and “Auto.” In the “On” mode, the fan runs all the time, 24/7. Continuous air circulation quickly fills the filter media with dirt and dust, requiring more frequent filter replacement. In the “Auto” mode, the fan runs only when the air conditioner or furnace cycles on. Using the “Auto” mode usually results in filter replacement intervals in the recommended range of one to two months.

High-efficiency filters.

Filter efficiency is expressed by the MERV (Minimum Efficiency Reporting Value) numeral. The higher the rating, the thicker the filter and the more particulates it captures. For residential use, filters in the MERV range of 8 to 12 are recommended for filtration capacity and optimum airflow. If a high-efficiency filter with a MERV rating above 12 is installed, however, the thick filter media will accumulate dirt and dust particulates faster and need changing more frequently than the recommended MERV 8 – 12 range.

Shedding pets.

All cats and dogs shed hair—some more than others. Pet hair typically becomes airborne and is drawn into the HVAC ducts and captured by the filter. Matted fur in the filter accelerates dirt accumulation and requires more frequent replacement. Brushing some pets outside may reduce indoor shedding and frequent vacuuming may remove shed hair before it becomes airborne.

For more about possible causes of a dirty air filter, contact the professionals at Rinaldi’s Energy Solutions.

Our goal is to help educate our customers in Orlando, Florida and surrounding areas about energy and home comfort issues (specific to HVAC systems).