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Where is the furnace filter and how often should you change it?

One of the easiest and cheapest ways to help decrease your utility bills, increase your home's comfort and increase the life span of your furnace is to regularly change your filter. With some systems it is easy to identify where the filter is while others it can be a bit more difficult, but for the most part all filters are in the same general area.

A standard air filter serves one main purpose, and that purpose is guessed it, filter your air! The point is to filter your air before it reaches your heating or cooling equipment! This means that the placement of the filter is not critical, just so long as it appears before the fan of the furnace or air handler.

The filter can be placed anywhere from just before the fan to all the way back to the return air grill. They can be inside the blower compartment, in a designated filter box or tucked into the duct work somewhere.

If you cannot find your filter, follow these steps to locate it:

  • Turn off the power to your furnace or air handler (usually a switch near the furnace).
  • Pull off all panels to the furnace.
  • Locate which compartment houses the blower (usually the part opposite where the burners are).
  • Look to see if the filter is in the blower compartment. If not, go on.
  • Check to see if there is another door on the duct work or a slot cut into it (could be on any side of the duct).
  • If there is no slot or door in sight follow the duct work back to verify there is no filter tucked away somewhere.

If you still have not found a filter the last place you can check is behind your return air grills. The return air grills are the usually located on a wall, not the floor, and draw air in instead of blowing air out. These types of filters are most commonly found in smaller homes with 1 or 2 return air grills.
If the filter is in the return air grill, you will want to remove the grill (some designs are easier than others) and replace the filter with one of the same size.

How often should I change my filter?

This is another debatable question and it can really depend on differences in homes. Smaller homes with no animals, few occupants and a cleaner environment can usually go a few months without changing. However, if you live in an average home with several occupants and own an animal, your changing time should probably increase to every month to month and a half.

Every home is different and how often you are running your equipment, where your house is located and even the style of filter can affect how often you should change your filter. For example, media filters, as they are commonly called, are very thick and have pleats to maximize surface area, these filters usually can be left in for 6 months to a year, but they are more expensive and your furnace usually has to be set up to accommodate these styles.

Bottom line is we recommend never going longer than 90 days with a standard filter and in most cases you will want to change them every 30 days for maximum efficiency and protection of your equipment.

How do I change my filter once I've found it?

Once you have located your filter and it is time to change it the process is very simple. In most cases filters just slide in and slide out. Occasionally you will find some sort of a bracket to work around or something running across it, such as a wire or spring, to hold the filter in place. A lot of filters are directional, so the last step is to be sure the arrow on the filter is pointing towards the furnace or air handler. If the fan comes on and the filter stays in place you have most likely installed the filter properly.

HVAC UV Lights for HVAC Systems

Do They Work?

In 1903, Niels Finsen won the Nobel Prize in Medicine for his use of ultraviolet light in the treatment of tuberculosis. Since then, ultraviolet lights have been widely adapted for all kinds of uses: sterilizing hospitals, sterilizing water, germicidal lamps in food establishments, and even curing nail polish faster. If UV light is so effective, how can it be applied to improving indoor air quality for residential HVAC systems? Will it kill mold and bacteria in HVAC systems? Yes, but you need to understand the priorities of indoor air quality and the types of UV lights available for residential HVAC systems.

Types of HVAC UV Lights

There are two types of UV lights for HAVC systems.

Coil Sterilization – A “stick type” light installed inside the air duct near that sterilizes the air handler coil. A coil sterilization UV light runs 24/7 and is the most common type of HVAC UV light. It is also most reasonably priced.

Air Sterilization – A complete UV light unit that sterilizes moving air. The UV light unit is installed in the return air duct and cycles on with the air handler blower.

Studies Prove Effectiveness

Two studies point to the effectiveness of UV light in killing mold and bacteria, one in hospitals and the other in a commercial HVAC system.

Ultraviolet Light Effective in Hospital Infection Control – In 2012, Researchers at Duke University Medical Center used ultraviolet radiation (UV-C) to nearly eliminate drug-resistant bacteria in 50 hospital rooms, reducing the number of bacteria by more than 97%.

Effectiveness of Germicidal UV Radiation for Reducing Fungal Contamination within Air-Handling Units – In this commercial office building, and after 4 months of operation, “the fungal levels following UV operation were significantly lower than the levels in control AHUs (air handler units).”


Usually bulb is estimated to last 9000 hours, just over 1 year. Replace the bulb during each annual HVAC service and maintenance is nearly effortless.

Indoor Air Quality Priorities

While HVAC UV lights are effective for killing mold, bacteria, germs and odors, make sure you have completed the indoor air quality basics:

  • Clean Air Ducts regularly 
  • Seal air ducts during renovation or construction
  • Install ducts in conditioned space
  • Ensure air-tight ducts, sealing all joints with mastic. See this Duct Sealing Guide from Building Science Corporation.
  • Install UV light in HVAC system
  • Conduct regular maintenance, changing filters monthly and cleaning the coil and furnace annually


HVAC UV lights:

  • Control mold and bacteria
  • Reduce colds and flus – germs are not re-circulated by HVAC system
  • Reduce smells / odors
  • Remove VOCs (Organic compounds are chemicals that contain carbon and are found in all living things. Volatile organic compounds, sometimes referred to as VOCs, are organic compounds that easily become vapors or gases. Along with carbon, they contain elements such as hydrogen, oxygen, fluorine, chlorine, bromine, sulfur or nitrogen).
  • Are more effective in humid climates than dry climates
  • Reduces clogging in condensate drain lines by preventing algae growth.
  • Maintain a cleaner coil, improving cooling efficiency and reducing electricity costs.

Bottom Line

HVAC UV lights are an effective means for improving indoor air quality, but only after following the indoor air quality priorities. Install an HVAC UV light and experience healthier indoor air quality.