Replacement Furnace Filter MERV Ratings Explained

If you haven’t spent a lot of time learning about them, you might think that all furnace filters are pretty much the same. However, there are many differences that can significantly impact the efficiency of your furnace and how effective it is at cleaning the air in your living spaces. When shopping for replacement furnace filters, you’ll need to know what MERV ratings mean, and what you should be looking for in a furnace filter for your home.

‘Out of sight, out of mind’, is how many people likely feel about furnace filters. After all, once they’re installed you don’t really have to worry about them until it’s time to replace them again. However, the role your furnace filter plays in keeping your home comfortable and the air you breathe clean is extremely important. This means it’s essential to make sure you’ve got a good quality filter in your home furnace that’s able to capture and control common airborne particles so you and your family can breathe easy.

What Kinds of Airborne Particles Should a Furnace Filter Capture?

Inside every home, no matter how many times you dust or vacuum, you’ll still find tiny particles floating around in the air. These particles include such things as common household dust, pollen from trees, grass or flowers, mold spores, pet hair and pet dander. Other things like sawdust or drywall dust are not unusual to find in the average home, particularly if a recent home renovation or repair has taken place.

The actual size of these airborne particles can vary quite significantly, with some being easily visible to the naked eye and some being extremely tiny and almost invisible. In order to keep the air circulating through your home HVAC system as clean as possible, your furnace filter needs to be able to capture and control particles that are between 10 microns and 0.3 microns in size.

Not all furnace filters perform this function with the same level of efficiency. In fact, some filters are far superior in their ability to capture and control those tiny airborne particles. This is particularly important for people who may have respiratory issues or are allergic to things like pet dander, pollen, or other common airborne allergens. So, how can you properly compare one furnace filter to another to know which provides the best level of filtration for your home? Well, let’s find out. It’s time to say hello to MERV!

What Does MERV Stand For?

For starters, no, MERV is not a reference to any person, but is an acronym for ‘Minimum Efficiency Reporting Value’. This rating system was developed to accurately gauge the effectiveness that a filter has at capturing airborne particles between 10 microns and 0.3 microns. The more particles in that size range that are captured by the filter, the higher the MERV rating will be.

MERV ratings start at 1, indicating the lowest level of particle capture efficiency, and go up as efficiency increases. Within the MERV rating scale, filters are assigned efficiency values as percentages for three different particle size ranges; 10.0-3.0 microns, 3.0-1.0 microns, and 1.0-0.3 microns. For example, a filter with a MERV rating of 8 is able to remove 70% of all airborne particles between 10.0-3.0 microns in size. Here is the complete MERV rating chart, along with a description of where filters of these ratings can typically be found.

What Are the Common MERV Ratings for Home Furnace Filters?

The most common base rating for a home furnace filter is usually a MERV 7 or 8, minimum. These filters are often specified by the manufacturers of home furnaces as the recommended minimum MERV rating. MERV 8 filters are an economical option for homeowners looking to keep their furnace operating efficiently and provide a good level of air filtration.

Now, the minimum recommended MERV rating is just the baseline to ensure proper furnace operation. You can select higher MERV ratings to achieve better control of airborne particles and keep the air in your home cleaner. For anyone who has allergies or might have a respiratory sensitivity, choosing a furnace filter with a higher level of air filtration is a wise move, as it will reduce the amount of airborne particles that can cause irritation and discomfort.

Filters with a MERV rating of 10 or higher are often marketed as ‘allergy control’ filters due to their higher efficiency at capturing dust, pollen, pet dander, mold spores, and other tiny airborne irritants. In many cases, the packaging for these types of filters will reference allergy control features quite prominently, along with a clearly marked MERV rating value. However, any furnace filter with a MERV rating of 10 or higher will be effective at reducing airborne allergens, regardless of whether or not the manufacturer chooses to label it specifically as an allergy control filter.

With this information now in mind, how can you decide exactly which furnace filter would be the best choice for your home and the needs of your family? There’s a few simple considerations that can help you narrow down the field and find the best filter for your furnace.

What Furnace Filter Should I Buy for My Home?

The first thing you need to know when choosing a replacement furnace filter is what size you’ll need. After all, it won’t really matter what MERV rating the filter has if it won’t fit in your furnace! To find the right size, there are several methods you can use. Most furnace filters have the size clearly visible and printed directly on the filter frame. If you shut off your furnace and remove the filter from its slot, you should see a reference number on it in a very prominent place that looks something like this: “16x15x3”. These three values refer to the length, width, and depth (thickness) of the filter in inches, and this is the number used to indicate the correct size of replacement filter you’ll need.

If you can’t see this size reference printed on the furnace filter itself, you can usually find this information in the furnace owner’s manual. If you don’t have the owner’s manual for your furnace, you can also download a digital copy from the manufacturer’s website simply by searching for the make and model of your particular furnace. The filter size is usually found in the section of the manual that details the parts list, or in the section regarding maintenance and service.

If you still can’t find the filter size, you can simply take a tape measure and measure the three dimensions of the filter to find out the correct size. Now, when measuring your filter, it’s important to note that the actual dimensions will be slightly smaller than the ‘nominal’ size that you’ll look for when buying replacements. For example, using the filter size we mentioned earlier of 16x25x3, the actual tight dimensions of the filter will be something like 15 ¾” x 24 ¾” x 2 ¾”. This is because the filter needs to be slightly smaller to fit snugly in the filter holding slot of the furnace. To make it easier to buy replacements that will fit properly, filter manufacturers just round these values up to the nearest inch. You can also measure the interior opening of the furnace air filter slot if you do not have the old filter to refer to. In this case, the measurements you obtain will probably be incrementally larger than the nominal filter size, so you’ll most likely be rounding down to the nearest inch.

Need more help in finding the right furnace filter size? Visit our Guide to Furnace Filter Sizes!

What Furnace Filter MERV Rating is Best for My Home?

Like we said earlier, a MERV rating of 8 is the basic standard for most home furnace filters in Canada. It offers a good balance of filtration efficiency and affordability. However, furnace filters with MERV ratings of 10 or 11, or higher, are surging in popularity as people look to improve the air quality in their homes, minimize allergy irritation, and have more peace of mind about the cleanliness of the air they’re breathing. If you or someone in your family is affected by seasonal allergies, pet allergies, or perhaps has some other type of respiratory concern, then a MERV rating of 10+ will be a wise choice for your home.

What About MERV Ratings of 16 or Higher?

When shopping for furnace filter replacements, you may also see MERV ratings that are much higher. However, not all home furnaces are compatible with filters of this level. You see, as the MERV rating increases, the restriction of airflow through the furnace also increases in order to more effectively capture tiny particles. While this helps capture more dust and dirt, it also reduces the volume of air moving through your HVAC system, and can reduce the overall energy efficiency of your furnace.

In general, MERV ratings of 13+ are considered more for air purifier systems rather than normal furnace filter replacements. In the event that your home does have a separate air purifier running in conjunction with your furnace, a MERV rating of 13 – 16 will most likely be specified as the recommended replacement for the air purifier unit.

Is a HEPA Filter Different from a MERV Rated Filter?

By definition, a HEPA (high efficiency particulate air) filter uses the same efficiency rating scale as MERV filters, but the term HEPA is only applied to those filters that exceed MERV 16 filtration values. A MERV 16 filter is rated to remove 95% or more of all particles between 10.0 and 0.3 microns in size. By comparison, a HEPA filter is rated to 99.97% particle capture efficiency.

HEPA filters are most often used in standalone air purification units, and not usually installed directly into home furnaces as a replacement for the standard furnace filter. In some cases, such as in commercial or industrial air quality applications, HEPA filtration systems can be integrated directly into the building HVAC system. These are highly specialized units designed for things such as medical clinics, laboratories, and other facilities in need of strict environmental controls.

What Else Should I Know About Buying the Right Furnace Filter?

If you’re interested in learning even more about selecting the right furnace filter for your home, we’ve got plenty of other handy resources and articles you can refer to. We encourage you to check out our Guide to Furnace Filter Frequency Changes and Guide to Furnace Filter Sizes for helpful tips, and browse around our blog to see what else is new and exciting in the world of furnace filters, energy efficiency, and home comfort. And if you have any questions, please feel free to reach out to us any time!