How to Determine the Air Flow Direction for a Furnace Filter

By Nathaniel Miller

  • Overview

    Each year millions of households turn their furnaces on (be they gas, wood or electric) and begin circulating warm air through their houses without even checking the filter in the furnace vent. The furnace filters are used to clean the air brought into the furnace (and in some cases blown out) in an effort to cut down on allergens and dust floating free in the air. Some households install new filters each year, but how effective are those filters? If installed incorrectly, the filters can have a negative or negligible impact on the air quality of a home. Installing a filter correctly simply involves finding the correct size filter and determining the air flow direction on the filter itself. This article will help you accomplish this goal with short easy steps.
    • Step 1

      Purchase filters based on the model number of your furnace. Locate each filter on the furnace and ductwork. Pull the old filter out of the duct and discard it.
    • Step 2

      You will now need to determine the airflow of the particular vent you are working with. Take a short length of string and suspend it inside the duct work. Turn the furnace on and see which way the end of the string is pulled. That is the direction of the airflow.

    • Step 3

      Examine the tops and sides of the furnace filter. There will be a marking on the top or side indicating the airflow for the filter. Insert the filter into the ductwork so that the airflow direction arrow is pointing the same direction as the airflow you determined in Step 2. Repeat Steps 1 through 3 for the remaining duct filters.
    • Skill: Easy
    • Ingredients:
    • Filter
    • String
    • Tip: If in doubt, the side with small holes or mesh is normally where air meets the filter, thus scrubbing out the majority of dust and allergens all at once.
    • Warning:
    • Do not crinkle the filters as you are installing them as this decreases their usefulness and could let dust and allergens through.

    © High Speed Ventures 2011