Guide to Furnace Filter MERV Ratings
When shopping for new furnace filters, it can sure be frustrating to read through all the specifications and technical information printed on the packaging or listed on websites. Often there are multiple acronyms and technical abbreviations used that need to be decoded in order to make sure you’re actually getting the right product. In fact, knowing how to read the different bits of information helps to ensure that the filters you buy are going to keep your home air as clean as possible, and help your furnace operate most efficiently to save you money on your energy bills.
One of the most common things you’ll see listed on air filters of all types, including home furnace air filters and air purifier filters, is a MERV rating. This is one of the most important pieces of information you’ll find on filter packaging and on product web pages, but what does it mean and what should you look for when choosing between different MERV ratings? Let’s get right to it!
What Do MERV Ratings Mean?
Filters come in many different styles, are made from different types of materials, and are designed to meet specific criteria for how efficient they are in removing particles from the air. To make it easier to gauge how efficient a filter is at capturing very small particles in the air, a standardized rating system was introduced. The value each filter is given to indicate this is known as the filter's Minimum Efficiency Reporting Value, or MERV for short.
MERV ratings are based specifically on how effective a filter is at capturing a particle sizes from 10 microns down to just 0.3 microns. MERV ratings begin at 1, and increase as the filter's efficiency increases. Here’s a simple chart that illustrates the different MERV ratings, including their efficiency measurement, and the typical use cases for filters of that rating.
What MERV Rating Should I Buy For My Furnace?
In general, the lowest MERV rating you’d typically want to have in your home furnace is about a MERV 8. Filters with this rating will be effective at capturing common household airborne particles such as dust, fibers, pollen, pet dander, and mold spores. In addition, most furnace manufacturers will specify a recommended MERV rating in the owner’s manuals for their household furnaces. In many cases, this will also show a MERV 8 rating, but there may be some furnace makes and models that require a higher MERV rating for the air filters. For this reason, it’s always important to check the furnace manufacturer specs to be sure you’re buying a filter that properly matches.
Now, just because a particular furnace may not specify a MERV rating for their filters, or if the MERV rating shows as 8 in the manual, this doesn’t mean you are limited to only using a filter of that rating. In many cases, you can upgrade the filter in your furnace to a higher MERV rating to provide cleaner air and more efficient capture of airborne particles for your home. However, you most certainly never want to go with a MERV rating that is lower than the minimum recommended rating. This can cause problems with the performance of the furnace and will also result in a lack of proper filtration and reduced air quality.
When looking at home furnace filters with higher particle capture efficiency, you’ll typically see those filters between a 10-13 on the MERV rating scale. These filters provide an excellent balance of improved air filtration and efficient air movement through the filter. This is important to note, as filters with very high MERV ratings of 14 or more will be more restrictive in the flow of air through them. This restriction is due to the higher rate of capture of particles, but may result in reduced overall energy efficiency of your furnace. Remember, just because the MERV rating is very high, doesn’t mean it’s the best filter for your home.
What If I Need an Allergy Control Filter?
In most cases, filters that are marketed as ‘Allergy Control’ are just filters with a MERV rating of 10 or more. In general, the use of terms like ‘Allergy Control’ on the packaging of furnace filters is just an easy way of distinguishing higher efficiency filters from those with lower efficiency. Since the meaning of the term ‘MERV Rating’ is not quite as widely known, Allergy Control is much easier to recognize at a glance. Ironically, this is actually part of the reason why we’ve created this guide for you! When shopping for furnace filters to help minimize allergens in your home, you can get just as much benefit from a filter with a MERV rating of 10 – 13 as you can from one that is heavily branded as an ‘Allergy Control’ filter.
Is a HEPA Filter Different From a MERV-Rated Filter?
The term HEPA filter is another one that you’ll find used in the context of home comfort, heating, cooling, and ventilation. The acronym stands for ‘High-Efficiency Particulate Air’ filter, and is used to distinguish filters with very high MERV ratings. Specifically, those filters rated on the MERV scale of 17-20 are generally considered to be HEPA filters. These filters are tested to capture 0.3 micron particles with 99.97% efficiency or higher, making them suitable for use in highly-controlled environments and spaces where air cleanliness is of utmost importance.
HEPA filters are not used in the same way that traditional furnace filters are used, and do not specifically replace existing furnace filters. HEPA filters act as additional layers of air filtration in interior spaces, cleaning the air again after it has already passed through the furnace filter and air ductwork of the building. HEPA filter units are often seen in medical buildings, dentist offices, long-term care facilities, and other spaces where contamination control is a priority. Home HEPA filtration units are also quite popular, especially for people who experience more severe environmental allergies or are in higher-risk groups for developing health complications due to airborne particles.
Does a High MERV Rating Mean I Don’t Have to Change the Filter As Often?
It’s understandable to assume that a better furnace filter might mean that they’ll last longer, but when it comes to MERV ratings, the two factors are unrelated. Choosing a higher MERV rating for your furnace filter will certainly do a better job of capturing those airborne particles as they move through your home HVAC system, but those particles don’t just vanish once they’re captured. Over time, the captured particles continue to build up in the filter, and it will need to be replaced on a regular schedule. The true determining factors of how often you need to change your furnace filter are things such as how large your home is, how often the furnace or air conditioner operates, how much traffic occurs in your home on a daily basis, whether you have pets, and other aspects like these.
As a simple guideline, most home furnaces will need their filters changed once about every 3 months, regardless of the MERV rating of the filter. For higher-traffic homes or those in environments more prone to dust and pollen, this frequency may end up being shortened to every 1-2 months to maintain a good quality of interior air for the home. It’s also important to note that home renovations tend to significantly increase the amount of dust and dirt in the air, so if you are currently undertaking a project like this, you may want to check your furnace filter to see if it’s dirtier than normal. If so, it’s a good idea to replace it sooner rather than later.
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