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No matter what type of HVAC system your home has, it most likely has an air filter. The purpose of an air filter is to remove particulates from the air.
When it comes time to replace your air filter, figuring out the size of your air filter isn’t the only thing you need to do. You also need to figure out what the best air filter MERV rating is for your situation.
What MERV Rating should I use?
Since a high MERV rating means that more particulates will be removed from the air, you may first think to only use air filters with the highest MERV rating.
However, a high MERV rating on an air filter also means that the filter is usually thicker, and your HVAC system will have to work harder to circulate air throughout your home. When your HVAC system has to work harder, it uses more energy.
Using an air filter with a MERV rating of about 5 to 8 is appropriate for most residential homes.
MERV 5 – MERV 8 filters provide good filtration and will remove most pollen, mold spores, and dust mites. Using MERV 5-8 filters will keep your HVAC system more efficient than using higher rated filters, as long as you replace your filters regularly.
If you are susceptible to allergies, asthma, or other respiratory conditions, then you may want to use a filter with a MERV rating of about 10 to 12. These types of filters are sufficient to trap particles as small as 1 micron such as automobile exhaust, pollen, and mold spores.
There are two main types of air filters: pleated and non-pleated. Generally, pleated filters have a higher MERV rating, while non-pleated filters have a lower one.
With a MERV 8 rating and mesh-reinforced construction, these filters block most household particles. Since they come in almost any size, these are our favorite pleated air filters to use.
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If you have allergies, get a filter with a MERV rating of about 10 to 12 to help relieve your symptoms.
Sometimes particles such as pollen, pet dander, and fine dust are able to sneak by your filter unless you get one with a higher MERV rating.
A filter with a MERV rating of around 10 to 12 is sufficient to remove most allergy-causing particles from your home’s air.
Most air filters that are able to remove common allergens will have the word “allergy” or “allergen” on their packaging. This is an indication that you’re on the right track.
Some of the best air filters for allergies have extra features such as a carbon layer to remove odors. These are suited for people that have pets or other sources of smells in their homes.
Be sure that your HVAC unit is able to accommodate air filters with a higher MERV rating. Some air filters, especially those with higher efficiency ratings, may impede airflow due to the enhanced air filtration.
However, this may not be such a huge issue for most homeowners unless they have a very large HVAC system. Check out our article on how MERV rating affects airflow for more information.
If you are changing the air filter in your home’s HVAC unit, then you will generally need two pieces of information:
1. Air Filter Size/Dimensions
The size of your air filter can be determined by looking at the old air filter in your HVAC system. Most air filters have their dimensions printed right on them.
If you do not have an old filter to figure out the measurements from, then you can measure the dimensions of the filter holder in your HVAC equipment.
Filters are rectangular shaped, so there will be a length, width, and thickness (usually 1” for residential HVAC systems).
2. Air Filter MERV Rating
MERV stands for Minimum Efficiency Reporting Value. The MERV rating system is intended to be used to determine the filter’s ability to remove particulates from the air.
An air filter’s MERV rating is a scale from 1-16 that describes the minimum efficiency of the air filter. A low MERV rating means that the filter does not remove as many particulates from the air.
Conversely, a high MERV rating indicates that the filter does a good job of removing particulates from the air.
What is the best MERV rating to use?
Depending on your air filtration needs, there is likely a MERV filter that meets your requirements. The table below shows the different MERV ratings and their typical uses as well as the typical material and shape that they are made of.
Typical Air Filter Material
MERV-1 to MERV-4
MERV-5 to MERV-8
MERV-9 to MERV-12
MERV-13 to MERV-16
How does the MERV rating system work?
The MERV system is the industry-standard air fitler rating system. It was established by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE).
ASHRAE standard 52.2 describes the methods and procedures for evaluating the performance of air filters as a function of particle size. In layman’s terms, it sets forth the minimum amount of particles that a filter must capture in order to obtain a specified MERV rating.
For instance, if an air filter can capture at least 20% of E1, 65% of E2, and 85% of E3 particles, then it will obtain a MERV 11 rating.
Air Filter MERV Rating Table
The table below shows the minimum threshold that a filter must perform at in order to obtain a specified MERV rating. As the MERV rating goes up, the filtration efficiency requirements get more stringent.
Minimum % of particles removed by air filter
(0.3 - 1.0 microns)
(1.0 - 3.0 microns)
(3.0 - 10.0 microns)
Higher-rated MERV filters must not only be able to filter out smaller particles, but more of them as well.
It should also be noted that filters on the lower end of the MERV scale are not even tested for efficiency at capturing E1 and E2 particles. That doesn’t mean that they won’t capture any E1 or E2 particles – it just means that they aren’t proven to capture them at a specified level.
What are E1, E2, and E3 particles?
E1, E2, and E3 particles are particle range sizes that are used in testing air filters to determine a MERV rating.
Starting with E1, these are the smallest particles that are tested. E1 particles range in the size from 0.3 to 1.0 microns in diameter. Typical particles in this size range are smoke particles and bacteria. Only filters with a rating of MERV 11 or higher are tested with particles in this size range.
E2 particles range in the size from 1.0 to 3.0 microns. Typical E2 particles include pet dander and E. coli. PM2.5 are particles that are 2.5 microns or less in diameter, so the largest PM2.5 particles are considered E2 particles. Only filters with a rating of MERV 8 or higher are tested with particles in this size range.
E3 particles range in the size from 3.0 to 10.0 microns in diameter. Typical E3 particles include common dust, pollen, and mold spores. Most air filters are able to capture E3 particles to some degree. However, higher-rated MERV filters are able to capture more E3 particles than lower-rated ones.
What is the MPR rating system?
The MPR rating system is an air filter rating system created by 3M. The main difference between the MPR and MERV rating systems is that the MPR rating system is focused on a filter’s effectiveness at removing E1 microparticles from the air.
Check out our article for information on the differences between the MERV and MPR ratings.
Air filter maintenance and replacement
Most home HVAC systems have disposable filters that can be thrown away when dirty and replaced with a new one. A clogged, dirty filter reduces the efficiency of your home’s HVAC system by making it work harder to push air throughout your house.
A dirty filter can also cause higher energy bills. When the air filter is dirty, less air is able to travel through your HVAC system, resulting in increased runtimes and reduced efficiency.
Central HVAC air filter maintenance
Most home central HVAC systems have disposable filters that can be thrown away when dirty and replaced with a new one. A clogged, dirty filter reduces the efficiency of your home’s HVAC system by making it work harder to push air throughout your house.
It is recommended to check your air filters once every month to see if they are dirty enough to need changing. Most people will need to change their filters at least every 2 months. If you have pets in your house, then you will probably need to change your air filter more frequently.
Generally, if you cannot see the filter media underneath the dust trapped on the filter, then the filter needs to be changed.
Split AC air filter maintenance
Some homes do not havecentral HVAC systems, but have split systems installed instead. Split systems have become popular in the recent years due to their energy efficiency and relatively low cost to install.
These systems typically do not have any ductwork, only refrigerant lines that run from the outdoor condensing unit to the indoor fan coil unit.
If you have noticed reduced efficiency or airflow from your split AC unit, then the first thing that you should check is its air filter. Split AC indoor units typically have reusable, washable filters that can be cleaned by rinsing out with warm water.
If your filter is really dirty with stubborn gunk and grime, then using coil cleaner can help get the grime off.
Is it time to change your air filter?
Changing your air filter is necessary to maintain the health and efficiency of your home’s HVAC system. Anytime your use your AC or furnace, the air filter will get dirty as dust and particles flow through the system and accumulate on the filter.
The schedule that you will need to change your air filters depends on factors such as your home’s location, activity, and presence of pets.
For most homes, the air filter will need to be changed every 1-3 months. However, you should check your air filter every month to see its condition and if it needs to be changed.
Activities such as home renovations, leaving doors to the outside open, and kids playing in the house can accelerate the accumulation of dust and particles on your air filter.
How to change the central AC or furnace filter in your home
Changing your HVAC system’s air filter is just about the easiest maintenance that you can conduct as a homeowner. Even though simple, changing air filters on a regular schedule has far-reaching implications such as improved system efficiency, extended system lifetime, and a cleaner home environment.
In most home HVAC systems, the filter is located in one of two places:
- In the return duct near the blower compartment. Look for a long metal cover plate between the air return duct and the blower. Some air filter access panels are clearly labeled as such and may even have instructions on how to change the air filter.
- In the return grille. The air filters in some HVAC systems are located right in the return grille inside your home. These filters tend to be easier to change since they are located in a central location inside your house. If the return grille is in your ceiling, you might need a ladder to reach the filter.
Be sure that the HVAC system is shut down, and turn the power disconnect off for additional safety. After the HVAC system is shut down, remove the air filter. Sometimes it helps to use a screwdriver to prop the air filter out of the holder.
When removing the old dirty filter, it may be necessary to have a plastic bag handy to put the dirty filter inside. The trapped particulates inside of the filter can easily become dislodged when handling the filter, so putting the old filter inside of a plastic bag can help prevent the spread of filter dust.
When removing the old filter, be sure to pay attention to which way the arrows point on the filter so you know which way the air filter goes in.
When replacing an air filter, be sure that the filter fits nicely into its slot. It may be helpful to use a screw or piece of material to ensure that the filter fits snugly in place. When an AC fan starts, the movement of air may cause the filter to slam against the inside of the unit if it isn’t secured properly.
Which way does the air filter go in?
The air filter direction is important for proper HVAC unit operation. Most air filters have arrows marked on them to indicate the direction that the air is supposed to flow through it. The arrow should point towards the blower, and point away from the return air duct.
If your air filter is in the return grille inside your home, then the arrow should point toward the wall or ceiling.
What happens if the air filter is backwards?
If you install the air filter backward, you likely won’t notice any immediate effects. As long as you promptly correct the filter’s orientation by installing the air filter in the correct direction, then you should suffer no problems.
However, if an air filter is installed backward and left to run like that, then the HVAC system will likely run less efficiently, consume more energy, and do a worse job filtering the air. This is because the filter is designed to meet its specifications when air flows one direction through the filter, not both.
Your air filter also runs the risk of collapsing since it is designed for air to flow in only one direction through it. Pleated air filters have a wire mesh that helps to maintain the structure of the filter.
The wire mesh should be on the downstream side of the air filter. In layman’s terms, the wire mesh on the air filter should be on the side that faces the blower fan.
If your air filter is installed inside the return grille inside your home, then the wire mesh should be on the opposite side of the grille, where it is not visible.
What about washable air filters?
Washable air filters can be reused over and over again. They are usually made of metal or plastic and can be cleaned with water. They are great because you don’t need to spend money on disposable air filters. But the tradeoff is that you need to clean them more often.