Furnace Filters. It’s easy to forget about them quietly working away, keeping your furnace clog free and air quality clean.

Yes, easy to forget about and then, suddenly it’s time to change them and, oh dear… So. Many. Questions.

Yes, at CleanAlert we often get asked about Furnace Filters, and if you ask us, the only stupid question is the one that goes unasked. So, we thought we put all your questions (and answers you can trust) in one easy to find place. Now you never need worry about the furnace filter direction again. You’re welcome!

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 air flow 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? Check out our handy guide to installing a furnace filter.

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 an 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 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.