Why Is It Important to Change Your Furnace Filter?

How Often Should You Change a Furnace Filter?

Your furnace is an essential part of your HVAC system, as it heats your home and ensures a warm, comfortable indoor temperature all winter long. Therefore, it’s crucial to keep your furnace in peak condition at all times by performing regular maintenance. This includes scheduling regular safety check-ups, addressing any irregularities as soon as they become apparent, and more.


Beyond general maintenance, it’s also important to change your furnace’s filters frequently. That way, you can ensure that the air in your house remains free of dust, mold spores, and other contaminants.


Let’s take a closer look at what furnace filters are and how often you should replace them.

What Is a Furnace Filter?

Modern HVAC systems for homes use advanced filtration technology that eliminates harmful particles, ensuring the air that flows through the residence is as clean as possible. Commercial buildings also have filtration systems on a larger scale, but these generally require a professional HVAC technician for adjustment and replacement.


If you look carefully at your home’s furnace, you will probably notice the filtration system near the connection between the furnace and your vents. In most residential HVAC systems, the filter is a thin panel that slides over the vent, forcing the air leaving the furnace to pass through it. The furnace filter can contain different materials that trap allergens and other particles, preventing them from entering the air inside your house.

Types of Furnace Filters

Furnace filters come in varying degrees of performance. Economy and low-grade filters will remove the least amount of particles from the air as they generally have the loosest filtration material. This means that they will only remove the largest particles that pass through the system.


High-grade filters are more expensive but offer much better performance. Smith and Co HVAC in Pasadena, MD recommends that our customers purchase furnace filters with the highest filtration grade. You can refer to the filter’s Minimum Efficiency Reporting Value (MERV) grade to determine its effectiveness. This number (ranging from one to 20) represents how fine the filtration material is and how many particles it will remove from the air.


Furnace filters are available in a variety of different materials and MERV ratings. The most common include:


  • Fiberglass Filters – Most fiberglass filters have a grade of two to three and are the cheapest option available. These are ideal for small residential units in areas with low particle counts in the air.
  • Pleated Filters – Disposable pleated filters made of cotton paper or polyester tend to have ratings around six and are only slightly more expensive than fiberglass products.
  • Electrostatic Filters – Disposable electrostatic filters have a rating of 10 and are generally affordable in standard sizes. However, custom sizes can be costly.
  • Pleated Cotton Filters – High-efficiency pleated cotton filters offer the best MERV rating (typically around 14 to 16) and are the most effective at removing particles from the air. 

Replacing Your Furnace Filter

The size of your HVAC system’s filter generally informs how often you need to replace it. One to two-inch filters usually last about three months, while four-inch filters remain functional for up to six months. Five-inch high-performance filters are the most durable and can last up to one year. However, if your HVAC system’s furnace filter is visibly dirty, it’s best to replace it as soon as possible.


While it’s possible to replace your furnace filter on your own, it’s best to call in a professional if you have any hesitations. That way, you can ensure the job is done correctly and that there are no issues with your filtration system.

Contact Smith & Company HVAC for High-Quality HVAC Service and Repair

Smith & Company HVAC is a locally owned and operated HVAC company serving Crownsville, MD, Pasadena, MD, and Annapolis, MD. We strive to provide our customers with top-of-the-line service to ensure they get the most out of their residential and commercial HVAC systems.

Whether you need to replace a dirty furnace filter or install a new air conditioning system, call Smith & Company HVAC for trusted professional HVAC repair services at (410) 874-0766.