Best furnace air filter

The best furnace air filter to use depends almost entirely on who you ask. You’ll get a very different answer if you ask an HVAC technician than if you ask your doctor. The reason is simple. They both see the purpose of the furnace air filter differently.

Of course, there’s a trade-off for each.

The best furnace air filter according to HVAC people

Best furnace air filter
On the left, you’ll see the filter your HVAC repair technician recommends. On the right is a 3M-brand air filter that’s something more like what your doctor would say is the best furnace air filter for most of the year, as it’s fine enough to block pollen. And no matter what kind of filter you buy, change it out before it looks like the one on the left. Collin Anderson/Flickr

Virtually every HVAC technician I’ve ever asked said the best furnace air filter to use is the cheapest one. Just get the ones that cost about a dollar and last 30 days, they say, and be religious about changing them out.

They see the purpose of a furnace air filter as keeping dust and debris out of the motor, and the cheap one-dollar filters do a fine job of that. In the meantime, since they aren’t too fine, they allow plenty of airflow through them, so the HVAC system doesn’t have to work too hard.

If your goal is peak energy efficiency and making your furnace and air conditioner last as long as possible with as little maintenance as possible, this makes lots of sense.

But the trade-off is lower air quality. The cheap air filters block the biggest dust particles, but they do little or nothing to block pollen, pet dander, airborne germs or viruses.

An HVAC technician will also tell you the most important thing is to change your furnace filter regularly. When your filter is completely fouled with dust, it doesn’t matter what the filter’s original rating was. It’s not letting any air through and it’s making your HVAC system work too hard, costing you more in the form of a higher electric bill and reduced life expectancy on your furnace.

The best furnace air filter according to doctors

If you ask a doctor, they want you to get a furnace air filter that blocks more than just dust. They want you to get a filter with a high MERV, MPR, or FPR rating.

MERV is the industry standard rating. MPR is a proprietary rating that 3M developed, and FPR is yet another proprietary rating that Home Depot developed. In all cases, a higher number is better, but the numbers don’t look anything alike, making them harder to compare.

So here’s a table with approximate equivalencies and what they block. This will help you compare different brands of filters you might find in stores near you.

MERV 6 MERV 8 MERV 11 MERV 13
MPR 300 MPR 600 MPR 1000-1200 MPR 1500-1900
FPR 5 FPR 7 FPR 10
lint, dust, pollen dust mites, mold spores pet dander, smoke, cough/sneeze bacteria and viruses

The higher the rating, the more the filter blocks and the higher your air quality. The tradeoff is that the higher rated filters cost more, and they make your blower work harder.

Also, the rating is much more important than brand. That’s one reason different brands and different stores use their own ratings. It makes price comparison more difficult, making it more likely that they’ll lock you in. But now I’ve told you their secret, so you can compare prices and buy furnace filters wherever you want.

What furnace air filters I use

I typically buy MERV 8/MPR 600/FPR 5 filters in the spring, summer and autumn. Then, when I remember to do it, I switch to a higher rating, ideally something in the MERV 12 or MERV 13 category, during the winter to try to keep colds at bay. But those filters are overkill during the rest of the year, generally speaking.

Allergies are getting worse due to the lengthened growing season due to climate change, and I’ve certainly noticed a difference the last couple of years. My kids have allergies too, so using a MERV 8-class filter keeps us all a bit more comfortable. I definitely notice a difference using a MERV 8 filter over using the cheap filters that cost a dollar. The MERV 8 filters cost around $3 apiece but they last longer, so the price premium over cheap filters isn’t as high as it may sound. The package says they last up to three months. It seems like I get about two months out of them, typically.

But if your allergies are more robust than mine, you’re not doing your HVAC system any harm by using the cheap furnace filters. Regardless of what it says on the package, your furnace and air conditioner are perfectly happy with the cheapest furnace filter you can find. Just make sure you change them often enough. Set a reminder on your phone to check your filter every 30-60 days. Your HVAC system, your wallet, and your health will all be better for it.

Saving money on highly rated furnace air filters

MERV 8-class filters aren’t too expensive locally, but the big-box stores charge a significant premium for MERV 13-class filters. They cost $20 at my local Home Depot store. They’re quite a bit less expensive from Amazon.com. Amazon sells Nordic Pure and Filter Buy brands for a good 25 percent less than Home Depot charges for a comparable filter. You might also consider stepping down to a MERV 12 filter, as they are almost as good and cost about 1/3 less.

Due to the cost of MERV 12/MERV 13 filters, using them year-round gets expensive. But they’re less expensive than missing work due to illness, so using them during cold and flu season can make good sense.

And if you’re strapped for cash, you can try to extend the usable lifespan of furnace filters by vacuuming the dust out of a filter and then reusing it. The cleaned filter won’t be quite as good as new, but it’s much better than keeping a clogged filter in use. This trick may let you get through the entirety of cold and flu season on a single filter. At $15-$20 per pop, that’s a savings you can appreciate.

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