Do I Need to Change My Filter Even if it Doesn’t Look Dirty?

filter doesn't look dirty

My filter doesn’t look dirty. Do I still need to change my filter? You know, I get this question a lot, and the heavy, heavy majority of the time the answer is yes. You do still need to change your furnace filter even if it doesn’t look dirty. Read on for details on why this is the case.

First, let’s assume your using a pleated filter instead of a cheap blue fiberglass filter. Those blue fiberglass filters are great for capturing the errant tree branch or piece of fruit that you no doubt regularly drop into your ducts, but not much else. So again, let’s assume you’re asking about a pleated furnace filter.

These more efficient pleated filters are designed to filter out a range of much smaller particles, those in the 3-10 micron size and smaller. For reference, a human hair has the relatively gargantuan diameter of approximately 75 microns (most research places it between 50 and 100 microns, depending on the person).

Think about it: the human eye has difficulty spotting/identifying the width of a human hair, and the particles trapped in these filters are 85-95% smaller than that. You’re not necessarily going to see the buildup when it’s time to change the furnace filter, but just because you cannot see it does not mean it isn’t there. Waiting to “see” the dirt buildup can have detrimental effects on your health and the health of your furnace.

So…do you need to change your furnace filter even if it doesn’t look dirty? Unless you changed it a month ago or so, the answer is likely yes. There’s a reason most HVAC contractors, utility companies, and air filtration companies recommend changing your furnace filter at least once every three months, and they say this without knowing what your filter even looks like.

I say at least because it depends on the type of filter you use and your living habits. If you have no kids or pets, maintain a clean home, and don’t have any allergies, by all means a MERV 8 Basic Filter from FilterSnap is all you need, and I’d change it every 3 months.

However, if you have kids and pets or are susceptible to seasonal allergies, I would change it more frequently and step up to a MERV 11 or MERV 13 filter, depending on the quantity of people and severity of allergy conditions. Before I got married to my allergy-riddled wife, I used MERV 8. Now I use a MERV 11. When kids or pets enter the picture, I’ll be stepping that up to a MERV 13.

Let’s come full circle and bring it back to the original question: do I still need to change my furnace filter even if it doesn’t look dirty? I hope I’ve been able to answer that question for you today (yes, you do), or at least provide you with some guidance going forward.

If you have any questions, please feel free to contact me, per usual: All circumstances are different, and I’m happy to weigh in if you’d like me to.


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