Furnace Filter and A/C Filter Basics

Furnace Filter and A/C Filter BasicsThe best thing a homeowner can do for their heating and cooling system is to check/change the filters between regular service visits. This doesn’t replace regular scheduled maintenance by your trained professional, but will improve the air you breathe and cost of operating your HVAC system.

First, we should point it out that the A/C filter and furnace filter is one in the same. Your heating and cooling system share the same fan and filtration to move air through your home or business all year long. There are no special tools or skills needed to replace your filter. The filter will be located in a filter-rack of the returning air ducts or inside the furnace air handler. If it looks discolored or dirty replace it with a new filter. When replacing your filter note the air direction on the new filter. The arrow or wire side of the filter should be facing the fan motor in your system. Remember to date the new filter for future reference.

A dirty filter impedes airflow. That’s easy to understand but the effects may not be so easy. Proper airflow is needed to efficiently move air in both cooling and heating modes. Low airflow decreases the efficiency of the system which cost you more money and increases your carbon footprint. Less air movement across the filter leaves more dust, dirt and pollen in the house for you to breathe. The air movement also cools your fan motor protecting it from overheating and premature failure.

Some symptoms of a dirty filter are:

  • Frozen system with no cooling
  • Tripping the high limit switch and shutting down the furnace
  • Motor failure
  • Dirty air inside and poor air circulation
  • Unable to maintain temperature

How often you need to change your filter(s) in your HVAC system is mainly determined by the operating environment and run time. The general rule of thumb is about every three months. Things like an older inefficient system, poorly insulated house, a high pollen count, maybe you like it warmer or cooler than most, have pets or active children will all decrease the useful life of a filter and require more frequent changes.

When selecting a filter, start with the MERV (Minimum Effective Reporting Value) rating:

  • 1-4 Low quality flat (most washable) filters. They do little to clean the air or protect your equipment trapping particles larger than 10 microns.
  • 5-8 Medium quality pleated filters. Sufficient for most needs. They filter down to 3 microns which will catch most molds spores.
  • 9-12 High quality pleated filters. Great for allergies, asthma and respiratory conditions.
  • 12-20 Generally used for hospital and food processing. Not recommended for residential applications due to air flow restrictions.

If you have any questions about anything we’ve discussed here, please give us a call and we will be glad to help 304-743-8895.



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