Which Way Do You Put A Furnace Filter In?


Believe it or not, there are right ways and wrong ways to insert an HVAC furnace filter. If a filter is not properly installed, it could cause problems with the furnace’s efficiency and cost you money.

It’s important to routinely monitor your air filters to prevent them from becoming clogged with dirt, dust or debris, and so they continue filtering the air you and your family breathe. Clean filters allow for better indoor air quality and improved energy efficiency.

When an air filter is clogged, the furnace has to work harder to do its job. One clue telling you when it’s time to replace your filters is when you no longer can see through the filter. If you are unsure when to change the filter, invest in an electronic air filter monitor that will tell you when it’s time to change it.

Related: 2 Ways An Air Filter Can Kill Your Air Conditioner and Furnace

Frequently Asked Questions

Which Way Does Furnace Air Flow?

Forced air furnaces recirculate air through a home: pushing air (cool or heated) in, and pulling spent air back in for another cycle. So air flows from your ducts, through the filter, and into the furnace.

What’s The Right Furnace Filter Direction?

If you are looking at a furnace filter, find the arrow that indicates the proper airflow direction. That arrow must always face toward the furnace and away from the return duct that carries the air in need of heating or cooling.

How Do I Install A Furnace Filter?

This is pretty easy once you’ve found the arrow mentioned above and inserted it with the arrow facing towards the furnace and away from the return duct. Need more help? Give Service Legends a call and we can help.

What Do Furnace Filter Ratings Mean?

All filters are rated using the Minimum Efficiency Reporting Value, or MERV, scale which goes from 1 to 20. The United States Environmental Protection Agency recommends air furnace filters with a MERV between 7 and 13 for most homes. Check out this chart to see exactly what the ratings mean: MERV Rating Chart and see below for more details on selecting the right filter for you.

What Are The Best Furnace Filters?

What’s the best furnace filter? Well, that all depends on how much you want to spend and what you’re trying to filter.

You need to be aware of the MERV scale (explained above). A furnace filter with a high rating can slow airflow too much, but a low-efficiency filter won’t filter dust very well. When selecting the filter, it’s important to strike the right balance and ALWAYS consult your furnace manual to see the manufacturer’s specifications.

For most homeowners, a MERV 7 or 8 pleated filter provides a good balance between cost and filtration efficiency. These filters trap 80 to 95 percent of the particles 5 microns and larger—more than enough for most homes. However, if you have family members with allergies or an impaired immune system, you may want to invest in a MERV 11 or higher filter. But be warned, you must change these filters regularly to protect your furnace.

How Do I Know If My Furnace Filter is Dirty and Needs Replacing?

There are a few different ways of checking whether the filter is dirty and needs to be replaced:

  1. Examine your furnace filter carefully for the buildup of dirt, dust and other contaminants. A large buildup can be a sign that it’s time to replace your filter.
  2. Listen to the sound of air moving through your furnace. If you remove the filter and there is a significant release of air pressure, this means the buildup of dust and dirt has reduced the effectiveness of the filter. It should be replaced.
  3. Keep an eye on the amount of dust and dirt building up in your home over a set period. If you notice an increase in the amount of dust and dirt on furniture and other household items, it may be time to change the filter.
  4. The easiest and most reliable way of telling whether your filter is dirty and needs to be replaced is installing a filter monitoring system like FilterScan Wifi. This provides automatic monitoring of your filter system and alerts you when it’s time for a replacement. Using FilterScan Wifi means you won’t ever miss changing the filter when it’s necessary to avoid damage or low air quality, nor will you waste money on changing a filter that is still working effectively.

Is It Time to Change the Filter?

Technology can be great for this! You can easily set reminders on your phone to let you know. If you don’t have a smartphone or smart thermostat, a calendar is a good way to remind yourself. Simply write yourself a note when it’s time to change your filter.

Another way to remember to change your filter is the season changing from fall to winter, winter to spring, spring to summer, and summer to fall.

When it’s time to change your filter, follow these six tips to ensure it is performed properly:

  1. Locate the filter. In most furnaces, the filter will be adjacent to the furnace and is inserted where the ductwork meets the furnace.
  2. Determine where on the furnace you can find the filter air box. Stand in front of the furnace and look for the ducts. Pull the old filter out and discard it.
  3. On the new filter, find the arrow indicating the proper airflow direction. The arrow must face toward the furnace and away from the return duct that pulls the air in need of heating or cooling. It’s smart to draw the airflow direction arrow with a permanent marker on the furnace or ductwork. It is also good to label the new filter with the date when you are changing it to help you keep track of how long it’s been between changes.
  4. Slide the new filter in with the arrow pointing toward the furnace.
  5. Replacing your air filter is not difficult. Remember that air flows from your ducts, through the filter, and into the furnace. The arrow on the filter should always point toward the furnace.
  6. The furnace or the filter air box most likely will contain the correct filter measurements for replacement filters or just check the filter itself.

Be sure you always have a new air filter on hand so you can change it at any time.

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