Lennox furnace is no newbie in the heating and cooling game, and if you have been rolling with household heating equipment over the years, you would have surely come across one. Breaking the ducks with the world’s first riveted steel furnace back in 1895, Lennox has been in the business of producing some of the best furnaces since then. We’ll help you choose the best filters for Lennox furnace from Lennox recommended merv rating. This has always been a delicate choice, and undebatable one at that, especially since these filters also act as an air cleaner.

While checking into the Best filters for Lennox furnace, we found out that there are also several Lennox recommended air filters in the market today, therefore picking a product becomes quite tricky, but with the right guide, you can be sure to come out satisfied.

There are several qualities to put into consideration in picking the best air filter for Lennox furnace to successfully make the right choice. A good example is the Lennox recommended merv ratings. The Lennox furnace filter airflow direction is also important when it comes to placing the filter in the furnace.

Another quick example is; Lennox furnace filter 20x25x5 in size wouldn’t match a furnace that doesn’t possess the exact same dimensions. In this article, we would be reviewing different filters for Lennox, peculiar to specific products or specifications, to ease things as much as possible for you.

What size filter does Lennox furnace take?

The size of the filter used by a Lennox furnace specifically depends on the model of the furnace itself. There is no single universal size that all Lennox furnaces use, but you are rather expected to check manufacturers’ recommendation, or measure the actual filter size of the furnace, and use those dimensions in purchasing a replacement.

Let’s even consider all the products reviewed in this article; no two filters having the same dimensions shows how diversified the actual Lennox furnace filter sizes would be.

Lennox furnace airflow direction – What you should know

Irrespective of your pick for the Best filters for Lennox furnace, Replacing a furnace’s filter is not actually as direct as it seems, as most people get confused when following a simply DIY procedure. This is mostly down to ignorance about the furnace airflow direction. Filters are designed in such a way that air is to be taken through on side (which is more porous) and released through the other side. When installed the other way round, it leads to a great deal of improper air circulation.

To install a filter properly, start by looking out for the arrow, which indicates the proper airflow direction. This arrow is always indicated by the manufacturers, and the proper way to place the filter is when the arrow faces the furnace and away from the return duct, which carries the air in need of heating or cooling.

With this knowledge, you can wave goodbye to poorly installing filters, and that’s just about what you should know about airflow direction.

Top 5 best filter for Lennox furnace in 2024

1) Lennox X6675 Carbon Clean 16 MERV 16 Filter 20-Inch x 25-Inch x 5-Inch 

Lennox X6675 Carbon Clean 16 MERV 16 Filter 20-Inch x 25-Inch x 5-Inch 
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  • High merv rating

With its merv number standing at 16 from a maximum of 20, this Lennox X6675 filter is really high up in rating, with performance on the job to match. It is very effective for removing contaminants in the air as small as 0.3 microns, along with a select few ultra-fine particles. This filter purchase also contains two packs with dimensions 24 x 20 x 9 inches.

  • Effective against ozone and odor

Asides the bleated surface design filters, which makes it trap dust as air flows through, the material of this particular product is infused with carbon for extra cleaning effect. The carbon coating makes it also very effective for removing odor-causing molecules as well as ozone in the air. The triple effect against contaminants, odor pollutants, and ozone molecules is one of the things which makes it special.

  • Long life span

Echoing the manufacturer’s words, this filter should be able to last for at least a year of regular usage. However, this is not always so, as it also depends on other factors like the duration it is used for, as well as the environment it is used in.

For easy monitoring, hold the filter up facing a light bulb, and if the rays of light cannot be seen through the filter, then it’s time for a replacement. Note that the depth is only about 4.375 inches and not 5 inches as advertised by the sellers.


  • High Merv rating of 16 making it the industry’s highest efficiency filter,
  • long-lasting life up to 1 year before replacement,
  • carbon-coated fiber matrix for odor and ozone removal,
  • can trap particles down to 0.3 microns,
  • purchase contains two packs


  • costs quite to purchase but is eventually more cost-effective over time,
  • Only suitable for Lennox healthy climate HCC20 product,
  • not a Lennox branded filter but rather produced by a generic manufacturer.

2) Lennox Carbon Coated X6672 Healthy Climate MERV 16 Filter 

Lennox Carbon Coated X6672 Healthy Climate MERV 16 Filter 
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  • Treated material surface

The Lennox carbon-coated xx6672 filter is not one of the regular filters you come across frequently in the market. Taking a closer look, it possesses some awesome qualities though it looks conventional. The major highlight of these qualities is in its material, which is hypoallergenic and antimicrobial treated for starters. This special treatment prevents the growth of mold or bacteria when collected on the filter over time, therefore keeping harm far away from you and also giving the filter a longer life.

  • Doubles as an electrostatic filter

This ordinary looking material also doubles as an electrostatic filter. Removing static electricity causing charges that are regularly found in dry air. The problem of static electricity is very commonly found in homes using a furnace, but with this filter, you can wave those irregular and unexpected tingles from touching metallic surfaces goodbye.

  • High merv rating

Its merv number stands at 16, and that speaks volumes about quality and performance. This allows the filter to effectively captures a 95% minimum of fine particles circulating in the air as small as 0.3 microns. This also includes dust, mold spores, and other bioaerosols.

  • Fits into different products

With dimensions standing at 24.5 x 16 x 9 inches, which is slightly smaller than the earlier reviewed X6675. This filter is designed to be used on no less than six different furnaces, including some which Honeywell filters like the fc35a1001 and fc100a1029 can fit in too.


  • hypoallergenic and antimicrobial treated surface against microorganisms,
  • electrostatic filter material for preventing the accumulation of static electricity,
  • two-pack purchase,
  • high Merv rating of 16,
  • multifaceted design means it can be used in up to 6 different products,
  • lasts a year before replacement is required


  • expensive to purchase but cost-effective over time compared to cheaper products,

3) Lennox Healthy Climate X8788 MERV 16 Filter – 20″ x 26″ x 5″ – Genuine Lennox Product

Lennox Healthy Climate X8788 MERV 16 Filter - 20" x 26" x 5" - Genuine Lennox Product
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  • Good merv rating

With Merv number at 16, this filter boasts a very good performance against contaminants in the air. Some of these include dust, pollen, and pet dander as small as 0.3 microns in size. If it is 0.3 microns and above in size, then it wouldn’t escape the pleating waves of this filter.

  • Decent life span

The life span of this filter stands at six months of usage. Though this might not be as impressive as some of its counterparts, it is still decent enough for those on a lower budget. Keep in mind that you might have to replace it before six months or even way after depending on usage.

The purchase of this product, however, comes with just one in the pack. Making it quite pricy since it only lasts about six months too. Adding the few extra bucks to get the next product that would last a year and comes with two packs, seems like a better option.

Note that the depth is only about 4 inches and not 5 inches as advertised by the sellers.


  • High Merv rating of 16 makes it effective against contaminants as small as 0.3 microns


  • lasts only about six months,
  • purchase contains only one pack,
  • its price compared to the quality and life span puts is in the expensive class compared to other filters around the same price

4) Lennox Corporation X7935 20X20X5 MERV 16 FILTER 

Lennox Corporation X7935 20X20X5 MERV 16 FILTER 
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  • Good Merv rating with micro glass material

This filter is made with a different type of material compared to all the other products reviewed earlier. With micro-glass material, though this filter still retains the up and down wavy pleated surface. It does so with a microfiber material, which is known for its fine texture as well as contaminant trapping ability. However, they also pose a risk of allowing a bit too much through, especially when the fabric is too porous.

  • Good merv rating

Like all the other filters on our review list so far, the X7935 is designed with a good Merv rating. This makes it effective against a wide array of household contaminations. Its number stands at 16, which nevertheless remains the highest for filters that are not HEPA classified.

Purchasing this filter comes with only one pack. Which actually puts it in the expensive range, and from experience, it is susceptible to mold infection. This filter is not very suitable for areas where moisture is predominant or an atmosphere concentrated with mold. As over time, they would start growing on the filter, posing more harm than good.


  • High Merv rating of 16,
  • micro-glass material filter,
  • lasts up to a year before replacement becomes necessary


  • purchase contains a single pack only,
  • susceptible to mold growth

5) X6673 Lennox 20x25x5 Merv 11 Filter Media 

X6673 Lennox 20x25x5 Merv 11 Filter Media
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The Lennox X6673 is the low end of quality pertaining to Lennox filters. Despite us tagging it “low quality,” it actually does a good job in cleaning. But not just good enough as many other Lennox filters. With Merv number standing at 11, the filter is only able to offer a decent filtering capacity of larger-sized particles greater than 1 micron. This leaves it well below the domestic standard of 0.3 microns, which only filters with Merv range 13 – 16 possesses.

This filter would also last for about six months before replacement is needed, though it depends on usage. Although this looks like a pretty decent life span, we were expecting a little more for its price. The good thing is that the purchase comes with two packs, therefore having you covered for technically a year.

Overall, this is a low budget filter, and unless you are looking for something ordinary to just fill in the gap, or you are on a really tight budget, then you shouldn’t settle for this. With a few extra tens of dollars, you can get much better quality and performance.

Note that the depth is only about 4.25 inches and not 5 inches as advertised by the sellers. Its dimensions are also about ½ of what the sellers say they are.


  • comes with two packs


  • low Merv rating of 11 makes it effective against particles larger than 1 micron,
  • its cost is too expensive for quality offered,
  • has a lifespan of only six months

5 Important Factors to consider in choosing the best filter for Lennox furnace

The essential features for selecting the Best filters for Lennox furnace are:

  • Merv rating:

The Merv rating of the filter is a direct representation of the category of contaminant it was designed to deal with, and how efficiently it can do the job. The higher its number on the scale, the more effective it is infiltration, and the smaller the particle sizes it can hold. The most recommended number for domestic usage is anywhere between a 13 to 16 range, which can hold as small as 0.3 microns.

  • Size:

The size or dimensions of a filter is all about the product it would fit into.

  • Lifespan/ quantity:

Though filters that last for a year and include two packs on purchase are more expensive, the extra $10 or $20 is worth it, compared to you have to purchase or use another every six months.

  • Cost:

How expensive a filter is, should be relative to its performance in reality. This means that although the best of the best might seem expensive, most times, they are well worth it. You might be getting 2 to 3 different qualities in one. Try to get the best of what you can afford according to your budget.

  • Other features:

It would be good to have some features around. Carbon coated for removing odors, electrostatic filters, and the antimicrobial treated surface is most useful. We recommend you purchase a filter with at least one of those.

What is the best MERV rating for furnace filters?

The best Merv rating for furnace filters is those in category 16. A filter with a Merv rating of 1 to 4 is only useful for holding large sized debris greater than 10 microns. Examples are bugs, dust mites, and other household particles flying around.

In basic terms, this is equivalent to the net in your windows. Filters with Merv of 5 to 8 captures particles greater than 3 microns, while 9 to 12 captures particles greater than 1 micron.

From the range of 13 to 16, they are able to trap as small as 0.3 microns, including smoke, sneezing droplets, bacterial and other contaminants. This category is the highest a furnace filter can go without satisfying the HEPA qualification criteria, and they are suitable for domestic, and hospital use. Beyond this class, is the 17 to 20, which captures virtually even the finest of particles? They are mostly used in scientific experiments rooms, and electronics manufacturing spaces.

The category 1 to 12 are too poor to fit the bill for furnace filters, while the 17 to 20 range is too high-end and expensive for domestic use. As a result, the best category is the 13 to 16, with filters that carry the Merv rating of 16 being the best option for your furnace.

Do High MERV restrict airflow in Lennox filter

With all things being equal, high Merv filters should not restrict airflow in Lennox filters. The condition of all things being equal is actually satisfied by two different parameters, which are; how old the furnace is, and how cloggy you let the filter become.

Most old furnaces are not able to generate enough airflow pressure to push through modern filters today, because back in the days, filter technology isn’t as advanced as it is now. An older furnace should be able to make do with Merv 8 filters and might struggle with restricted airflow for any other thing higher.

Now, let’s assume it is a recent furnace. They are built to work with the more advanced filters of up to 20 Merv rating, and would only experience restricted airflow when the filter becomes too cloggy as a result of users failing to replace it in time. High merv rate filters are able to trap more contaminants than the low-level ones, making them get cloggy much faster.

It is important to keep an eye out on the filter life because poor airflow can easily cause damages to the furnace that would cost you a lot of money to fix. On the other hand, satisfy the non-clogging requirements, and you should not experience any restriction in airflow.

Final Verdict – Lennox Recommended Merv Rating

Lennox X6675 Carbon filter is the best amongst the crop of filters available for Lennox filters, and rightfully so. It possesses awesome qualities being carbon-coated, which makes it effective against ozone and odor as well as fundamental trapping of air contaminants, and has a Merv rating of 16, the height of filters which aren’t HEPA qualified. With a life span of 1 year, it’s got you covered all year round, and its purchase contains two packs.

Lennox Carbon Coated X6672 filter is the only worthy opponent in quality and performance. Being also carbon-coated, this filter also deals with odor-causing molecules in the air, as well as electrostatic charges, while offering the basic filtering of particles down to 0.3 microns in size. It also comes in a size that fits into numerous Lennox products and has an antimicrobial treated surface.

Important Reviews: