How Does an Air Filter Affect Furnace Efficiency?

Out of sight, out of mind.

Take healthy foods or exercise equipment, for example. If it’s out of sight, then we won’t think to act on it. The same goes for our air filter MERV ratings, furnace maintenance, and a variety of other factors that seem unimportant to our daily lives.

We are often so busy as tenants or homeowners that we don’t stop to think about the invisible things that need maintenance around the house, and air filters are the most common thing to go unnoticed for a long period of time.

In this article, you will learn several benefits of installing a new filter in your furnace, how you can tell if your furnace needs a new filter, and the general recommended air filter MERV rating that is required in residential units.

Benefits of Installing a New Air Filter in Your Furnace

We all know that replacing an air filter is something that we are supposed to do, but do you know the benefits from the simple action?

It is surprising to learn the symptoms of a poor air filter, how prevalent it is in our daily lives, and how easy it is to remedy. We just need to remember that air filter replacement is periodically needed.

Here are some of the benefits of replacing an air filter:

  • Improved Air Quality

The number one benefit to installing a new air filter in your furnace and keeping it regularly maintained is the vast improvement in your home’s air quality. There have been demonstrable effects on how clean air affects not just your quality of life and cognitive function, but also your personal health. (1)


“Research has shown that those living close to refineries, plants and interstates see higher rates of asthma, heart attacks, strokes and deficits in lung function that can lead to a lifetime of health problems.”

  • Mario Koran, The Guardian


If that wasn’t enough of a reason to keep on top of your indoor air quality, choosing an air filter MERV rating of 9 is ideal for removing common allergens from the air, keeping allergens out of the air and improving your indoor allergy symptoms.

  • More Energy Efficiency

Changing your filter not only influences your overall health and well-being, but also affects the financial health of your wallet. A dirty furnace can skyrocket your utility bills, so if you find that you’re using more energy or heating than usual, your air filter might be the culprit. Your costs may fluctuate with the seasons, but a sharp spike in your energy or heating bill may indicate a dirty furnace.

Choosing the proper air filter MERV rating is key to a sustainable energy bill, lowering your overall costs, and keeping your health in check. If your unit can push air through the vents, capturing particles while remaining unclogged, you have found the right air filter for your home.

Beyond the effects it has on your heating bill, choosing a pleated air filter can help reduce landfill waste. Pleated air filters are made of a biodegradable fabric, rather than spun fiberglass. A better, more efficient unit not only makes you happier, but it will make the environment happier, too.  

  • Extends the Life of Your Furnace

Maintaining your furnace and choosing the right air filter rating is key to extending the lifetime of the unit. A clean furnace is a happy furnace that will work for years to come.

A clean air filter means your furnace does not need to work as hard to pump air through the vents, the heating element works well, and the unit undergoes less overall strain. In turn, this means the unit is easier to service if it needs repairs, and it lasts longer.

On average, a furnace is meant to last between 15 and 20 years, but this time can be extended with proper, pro-active maintenance. Furnaces that have been poorly maintained may only see a 10-year lifespan before it needs to be replaced.

Keep your furnace around longer by frequently replacing the filter, remembering the MERV rating appropriate for your unit.  

Key Indicators That Your Furnace is Losing Efficiency

If you begin to suspect that your furnace is losing efficiency, your furnace might not be working as intended. We don’t always know the reason behind it, but noticing small changes in how something in our environment is performing can tip you off to the truth faster than a dirty air filter.

Here are some of the ways to tell if your furnace is underperforming.

  • Dirty-Looking Filter

The best thing you can check if you suspect your furnace is losing efficiency is your air filter. Does it look dirty or clogged?

If it has been a while since your last air filter change, it may be time to replace the filter. The time between changes can vary depending on the quality of your filter, how many people are in the home and how frequently, and if you have pets. If anyone in your home has allergies and you have pets, it is recommended you change the filter every 20 to 30 days if it looks dirty. With pets or more people in the home, the air filter is pulling more pollutants in from the air, and it will become clogged faster.

A filter can appear dirty even if it has just been replaced if the air filter MERV rating was not appropriate for the filter. If you see this, it’s time to change the filter and go to a lower MERV rating. A MERV rating that is too high for the furnace can block the air flow and cause it to clog faster.

  • Loss of Heat Output

It is not difficult to notice the heat pump failing in your furnace. If you are turning the heating controls up and it still won’t reach the set temperature, your filter might be clogging the hot air flow and causing the heat pump to overwork itself.

Over time, this can cause the inner workings of the unit to burn up if the problem goes unchecked. This skyrockets your heating bill in the short term, and can also cause the heat pump to fail. Replacing the heat pump is a costly repair that is more hassle than changing the air filter regularly, so it’s worth a little time and money upfront to avoid larger problems with in the future. 

  • Poor Airflow and Loss of Pressure

Poor airflow is another indication your furnace is losing efficiency. In many cases, this will also cause the heat to build up inside the unit and damage internal parts if the problem goes unchecked.

You can check this by replacing the filter. If you notice an increase in airflow after changing the filter, then your filter was clogging the airflow. If the filter wasn’t dirty, then it might be time to find a lower air filter MERV rating.

  • New Symptoms of Allergies or Sickness

Unexplained sickness or new symptoms of indoor allergies can be caused by new pollutants getting recycled into the air in your home. If the air filter is dirty, it catches fewer particles of dust, dander and pollen. The pollutants will filter right back into the air, and a buildup can cause physical symptoms affecting your health, immune system, and mental cognition. (2)

“Pregnant women, infants, toddlers and children, and persons who are immunocompromised, as well as those suffering from allergies and asthma are particularly vulnerable to the effects of indoor toxins.”

  • Janette Hope, MD

These symptoms are important to take seriously because poor indoor air can have longterm effects on the body.

What MERV Rating Can Your Furnace Handle?

If you suspect that your air filter MERV rating is too high for your furnace, keep an eye out for signs that your furnace is working harder than usual, or is less efficient than other furnaces of the same type.


“A MERV rating that is too high for the furnace can block the air flow and cause it to clog”

  • CleanAir


Typically, your furnace will have the recommended MERV rating on the information panel. This panel will also tell you how to install your filter, and any other specifications your individual unit might have.

If you are unable to find the information panel, any identifying information about the unit would be useful, allowing you to search the model number or name online to find more information.

The manufacturer’s website should provide information about its lineup of furnaces, including how often they recommend replacing the filters and instructions on how to change the filter.

General Recommended Air Filter MERV Rating for Residential Furnaces

So, how do you choose the right air filter for your unit?

Any residential filter will typically fall somewhere between a 4 and 12 MERV rating. Unless you have a top-of-the-line furnace, you will not need anything more than MERV 9.

A 4 on the MERV scale will be the cheapest filter available, but it will not catch the smaller particles such as dust and pollen. MERV 12 will help filter pollen dust, and other allergens out of the air. It may also capture smaller bacteria particles that float through the air. This is ideal for households that need to take severe allergies or immunocompromised individuals into consideration.

MERV 9 is the MERV rating for a standard, allergen-reducing filter that can be used in the home without risk of blocking the unit early. It’s the perfect balance between efficient and effective.

Which Do We Recommend?

CleanAir recommends an air filter MERV rating 9 for common households with pets or individuals with mild allergies. These air filters should be kept in the unit for no longer than three months and should ideally be changed every 1 to 1.5 months.

Do you want to keep the benefits of a clean air filter without the hassle of buying and installing the filter?

CleanAir delivers air filters right to your door with our air filter subscription service. We offer optional installation services. Simply select your filter and delivery frequency and your home’s air can go back to being out of sight, out of mind. Our service team will deliver the filter right to your door. There’s no delivery fee, no catch, just clean air and worry-free convenience. Sign up today to experience the benefits of clean air delivered to your door.


  1. The Guardian
  2. Forbes