Can a High MERV Rating be Too Much for Your Furnace?

Learn about how high MERV ratings can affect your furnace and what precautions you should take when using them.

Can a High MERV Rating be Too Much for Your Furnace?

If your furnace's MERV rating is too high, it can force it to work too hard and leave it vulnerable to damage. In addition, you may not get the air velocity needed to reach all parts of your house, leaving inconsistencies in temperature. The short answer is that it can, but it's not really a problem except in extreme circumstances. Most modern HVAC systems have no problem working with higher MERV filters, so millions of homeowners rely on them.

The main risk of high-efficiency air filters comes from the fact that they remain unchanged for long periods of time. If you're aware of changing your filters, you're unlikely to experience filter-related issues with your HVAC system. The AC coil inside or near your furnace or air handler gets very cold as it draws heat out of the space and pumps it out. A normal flow of warm air over the coil will prevent its surface from falling below 32°F.

Low airflow allows the coil to freeze cool. Then the moisture in the air freezes and the coil is covered with ice. At that time, the air conditioning system cannot do its job. The goal of using a MERV 12 or higher filter is a better IAQ: cleaner, more breathable air for everyone, and especially for those with allergies, asthma, COPD, etc.

If you are in a situation where you should not use a high MERV (12+) filter for your oven or air conditioner and would like to research air purifiers air, here are two suggestions. In general, filters with higher MERV ratings capture higher percentages of particulates as well as smaller particles. And MERV-13* is practically where you want to be. Generally, a filter with a higher MERV rating will reduce airflow.

However, there are many other factors at play, such as the size of the filter and the type of fan motor of the HVAC system.

Merv 11

air filters are a little more expensive than a standard filter, but paying a few extra dollars per filter is usually worth it for the added efficiency. Fortunately I have a 3D printer and have printed a mask with a MERV 13 filter. I'm wearing a MerVi cape.

I am using a layer of Merv 1900 3M Filtrete on my mask (I made the mask as a cover so I could remove the filter to wash it). Air filters that are MERV 13 and above are recommended for those who prioritize air quality and may have to handle asthma, severe allergies and other similar circumstances. A MERV 13 filter will probably help if the goal is to prevent droplets from passing through it. While air filters with a one-to-four MERV are effective at removing large particles such as carpet fibers, airborne paint droplets and sanding dust, they cannot help with contaminants such as hairspray, mold spores or even flour that might have escaped from the mixer.

Therefore, filters that are above 13 in their MERV rating can filter particles closer to the size of 0.3 microns. MERV 13 filters, for example, also remove bacteria, tobacco smoke, car fumes, insecticide dust, pet dander and more. It is best to adhere to the oven manufacturer's recommendations or consult an HVAC professional to determine exactly which MERV rating is best for your specific system. Many people don't consider how a filter with a high MERV rating will affect other parts of the HVAC system.

The MERV rating system ranges from 1 to 20, with the highest rating (20) being the rating used for filters in places such as hospitals.