What Is The Difference Between MERV 4 And MERV 8

It is common for users to go for furnace filters with low MERV ratings to protect their HVAC systems. However, it is important to balance the need to maintain a high Indoor Air Quality and protect the HVAC system.

In this article, we shall look at two low MERV ratings, 4 and 8.


MERV 4 is ideal for trapping large contaminants that measure about 10 microns in diameter. Mainly, this class of contaminants includes the following: carpet fibers, dust, sawdust, and textiles.

It also includes pollen and small particles from textiles. Such contaminants are primarily found in homes because they come from equipment and surfaces used in homes, including seats and carpets.

The only significant drawback of using MERV 4 furnace filters is that such devices do not capture small particles. The surfaces of MERV 4 furnace filters are not designed to trap microparticles that are as small as 1.0 microns in diameter. As a result, you will be forced to get a furnace filter with a slightly high MERV rating for such contaminants.


MERV rating is a good balance between high and low MERV ratings. On the one hand, MERV 8 furnace filters can capture a high percentage of large amounts and a reasonable percentage of small ones. Typically, furnace filters with this MERV rating are powerful enough to trap particles ranging from 3 to 10 microns in diameter.

Typically, MERV 8 is enough to trap the following types of contaminants, dust from concrete, mold spores, and carpet fibers. In addition, the furnace filters can also trap the small hair particles that usually come from pests.

This furnace filter is neither high enough to cause airflow restrictions nor too low to miss some of the most common forms of household contaminants, including spores. Air filters with MERV ratings of about 12 and above are notorious for causing airflow restrictions.

Similarly, meager MERV ratings are awful for ensuring that all the small contaminants that may be found in the air in your home are removed. Thus, using MERV 8 can keep your home completely clean and safe for a long time.

Is MERV 4 Good Enough?

MERV 4 is good enough for removing large solid contaminants. Furnace filters with this MERV rating can help keep your home clean because they will effectively attract and trap large contaminants, including dust and pollen.

This means that furnace filters with a MERV rating of 4 are powerful enough to keep people free from dust and pollen. Dust and pollen are the leading causes of allergic reactions. People who are sensitive to them react violently when they breathe air full of dust and other large particles.

Installing a furnace filter with a MERV rating of 4 is enough to keep the air free of such contaminants. Thus, such a furnace filter will keep people inside the house comfortable and free from allergic reactions.

However, MERV 4 is not enough for keeping your home free of small-sized contaminants. Small contaminants from aerosols can linger in your indoor air environment for a long time. The presence of such contaminants can seriously undermine the quality of the air in your home.

Therefore, it is necessary to have a furnace filter with a MERV rating that is high enough to trap and remove such contaminants. Sadly, MERV 4 is not good enough for removing such contaminants.

Is MERV 8 Good Enough?

MERV 8 is good enough for maintaining a high Indoor Air Quality in your home. Furnace filters with this MERV rating are ideal for removing large contaminants.

They can successfully filter up to 80% of large contaminants, including dust and pollen. Therefore, such furnace filters are good enough for keeping the indoor air environment in your home clean and safe.

You can experience the maximum performance of your MERV 8 furnace filter by choosing one that has a pleated and electrostatically charged surface. Unfortunately, such furnace filters can attract and trap large amounts of contaminants.

However, a MERV 8 furnace filter is not ideal for trapping small contaminants. Such a furnace filter will not sufficiently trap small contaminants like the microdroplets that come from aerosols, air fresheners, and even hair spray. Such contaminants can linger in the air in your house for a long time. You may have to get a furnace filter with a slightly higher MERV rating to remove the small contaminants.

Therefore, if your house is not particularly dirty, a MERV 8 furnace filter may be enough to keep the air clean. More so, a MERV 8 furnace filter will hardly interfere with the blower of your HVAC system. Thus, such a furnace filter is safe and effective.

Does MERV 8 Restrict Airflow?

MERV 8, just like other low MERV ratings, does not restrict airflow. A rule of thumb is that the higher the MERV rating, the higher the ability to restrict airflow. Similarly, the lower the MERV rating, the lower the ability of the furnace filter to restrict airflow.

Airflow restriction occurs because of the MERV rating of the furnace filter. Higher MERV ratings are associated with high-pressure drops. The higher the pressure drop of a furnace filter, the lower the airflow. This means that furnace filters with high MERV ratings have high-pressure drops and high airflow restriction levels.

In addition to the MERV ratings, other factors, including the size of the furnace filter and the type of blower that you use in your HVAC system. The higher the surface area of the furnace filter you use in your house, the lower the level of airflow restriction. This means that furnace filters with low face areas are more likely to cause airflow restrictions than those with high face areas.

Therefore, when choosing a furnace filter, go for those with relatively low MERV ratings. If you go for MERV ratings of about 14, you will experience airflow restrictions. This is because of the high-pressure drops that are associated with high MERV ratings.

Is a Higher MERV Better?

A Higher MERV rating is better if you are keen on maintaining a very high Indoor Air Quality level. For example, high MERV ratings of 12 or higher are best for ensuring that your furnace filter traps all small and large contaminants that may be found in the air inside your home.

Installing such a furnace filter will ensure that the indoor air in your house is relatively clean. However, such high MERV ratings come with an unintended consequence. The furnace filters usually interfere with the airflow.

Furthermore, the furnace filters may cause damage to the components of your HVAC system. This means that you may be forced to spend additional money to repair your furnace filter if one of the components gets damaged.


Low MERV ratings are ideal for removing large contaminants and keeping your HVAC system. However, low MERV ratings fail to trap small particles, which may lower the Indoor Air Quality of your home.

High MERV ratings, on the other hand, are ideal for removing microparticles in your home. Such furnace filters are designed to attract ad trap small particles that measure even up to 3 microns in diameter. However, they may interfere with the flow of air in your HVAC system.

High MERV ratings can also cause damages to the components of your HVAC system. Repairing such components or replacing the entire HVAC system is often a costly endeavor.