Is It Time to Replace Your Furnace Filter? Signs to Look for and Common Filter Sizes to Know

It's that time of year again - the cold weather is settling in and we're relying more and more on our furnaces to keep us warm. But when was the last time you checked your furnace filter? If you can't remember or the answer is "never," it's time to read on.

Having a clean furnace filter is crucial not only for your comfort, but for your health as well. Dust, pollen, and other allergens can accumulate in the filter and get recirculated throughout your home, exacerbating respiratory problems and causing discomfort. So, how can you tell if it's time for a new filter?

In this article, we'll walk you through the signs that your filter needs to be replaced and the common filter sizes you should know about. By staying on top of your furnace maintenance, you can ensure a cozy and healthy winter season for you and your family.

Signs that Your Furnace Filter Needs to be Replaced

One of the most crucial appliances in your home during winter months is your furnace. It keeps you warm and comfortable when the temperature outside is freezing, but it also requires regular maintenance to function efficiently.

One of the essential maintenance tasks is replacing the furnace filter, which can affect the air quality, energy efficiency, and lifespan of your furnace. Here are five signs to look for to determine if your furnace filter needs to be replaced:

Reduced airflow: If you notice that the airflow from your vents seems weak or not as strong as usual, it could be due to a clogged filter.

Unusual odors: If you notice a burning smell or a musty odor, it could be an indication that your furnace filter needs to be replaced.

Increased energy bills: A dirty or clogged filter can decrease your furnace's energy efficiency, resulting in higher energy bills. Replacing the filter can help lower your heating costs.

Presence of dust and debris: If you notice an accumulation of dust and debris in your home, it could be a sign that your furnace filter is not effectively trapping airborne pollutants and particles.

Allergy symptoms: If you or your family members experience frequent allergy symptoms like coughing, sneezing, or itchy eyes, it could be a sign of poor indoor air quality, which could be caused by a dirty or clogged filter.

Make sure to replace your furnace filter regularly to improve the indoor air quality in your home, reduce energy costs, and extend the lifespan of your furnace, saving you money and ensuring your comfort throughout the winter season.

How frequently should you replace your furnace filter?

The recommended time frame for replacing your furnace filter is every 1-3 months.

However, there are several factors that can affect the replacement frequency. If you have pets or a large family, your filter may get clogged more quickly and need to be replaced more often. Similarly, if you live in an area with high pollution or construction, your filter may experience a high volume of particles and require more frequent replacement.

To keep track of your filter replacement schedule, it's helpful to set a reminder on your phone or calendar. You can also check the filter regularly and note any changes in its appearance or performance. A dirty or clogged filter will restrict airflow and decrease the efficiency of your furnace, causing higher energy bills and potential damage to the system.

By staying on top of your filter replacement schedule and being aware of the factors that can impact its frequency, you can ensure your furnace is running efficiently and effectively, keeping your home comfortable all winter long.

Different Types of Furnace Filters

When it comes to purchasing a furnace filter, it's important to understand the different types available to determine what will work best for your home. Here are five common types:

a. Fiberglass filters: These are the most affordable and widely used furnace filters. They consist of layered fiberglass fibers designed to trap large dust particles and debris. However, they offer little protection against pet dander, pollen or other allergens.

b. Pleated filters: Made of cotton and polyester, these filters are folded in a zig-zag pattern, creating more surface area to capture smaller particles. They're more effective than fiberglass filters at cleaning the air, but also need to be changed frequently.

c. Electrostatic filters: These filters use electrostatic charges to capture particles. They work especially well to remove cigarette smoke, but can be expensive and may produce ozone.

d. High-efficiency filters: Sometimes called HEPA filters, these are some of the most effective filters on the market. They can trap small particles like bacteria and viruses, but may cause strain on your furnace's motor and need to be changed more often than other filters.

e. Advantages and disadvantages of each type: It's important to consider your budget, household needs, and maintenance requirements of each filter. Fiberglass filters are affordable but offer limited protection while high-efficiency filters provide top-notch protection but also carry a higher price tag and require regular replacement.

No matter what type of filter you choose, it's recommended to change it every 1-3 months. Doing so can extend the lifespan of your furnace, keep the air in your home clean, and prevent costly repairs.

How to Change Your Furnace Filter

Changing your furnace filter is a simple task that can be completed in just a few easy steps. Here's what you'll need and how to safely replace your filter:

Equipment and Tools You Will Need:

  • New filter (make sure you purchase the correct size)
  • Gloves (optional for safety)
  • Screwdriver or other tool to open the filter compartment (if required)

Steps for Safely Replacing the Filter:

  1. Turn off the furnace: Before beginning any work on your furnace, turn off the power supply to ensure your safety.
  2. Locate the filter compartment: The filter compartment is typically located near the furnace's air intake. It may be behind a metal panel or inside a plastic housing.
  3. Remove the old filter: Carefully remove the old filter from the compartment. Take note of the direction of the airflow arrow, which is typically printed on the frame of the filter.
  4. Install the new filter: Insert the new filter into the compartment, making sure to follow the direction of the airflow arrow. Ensure the filter fits snugly into the compartment.
  5. Turn on the furnace: Once the new filter is securely in place, turn the furnace back on and enjoy improved air quality in your home.

Tips for Proper Disposal of the Old Filter:

Proper disposal of your old filter is essential to ensure safety and environmental responsibility. Here's how to do it:

  • Check your local regulations: Before disposing of your filter, check your local regulations for proper disposal guidelines. Some areas may have specific requirements.
  • Seal in a plastic bag: Once the old filter has been removed, seal it inside a plastic bag to prevent any remaining dust, dirt and debris from escaping.
  • Place in the trash: Finally, place the sealed bag in your household trash for proper disposal.

By following these simple steps, you can keep your furnace filter clean, your air quality improved and your home environment safe and healthy. Remember to check and replace your filter regularly, following the guidelines set out by your specific furnace model, for optimal performance and longevity.

Common Filter Sizes and Types for Furnaces

When it comes to choosing a furnace filter, one of the most important factors to consider is the size. Here are the common filter sizes for furnaces:

a. Standard sizes: The most common standard sizes for furnace filters are 16x20 inches, 20x20 inches, and 16x25 inches. These sizes are readily available at most home improvement stores and online retailers.

b. Custom sizes: If your furnace requires a filter size that is not available in standard sizes, you can purchase custom-sized filters. Just make sure to measure your filter slot accurately before ordering a custom size.

c. Matching filter size to furnace specifications: It's important to match the filter size to your furnace's specifications. Check your furnace manual or consult a professional to determine the right filter size for your furnace.

d. Choosing the right filter for your needs: There are various types of furnace filters available, including fiberglass, pleated, and high-efficiency filters. Consider your indoor air quality needs and budget when choosing the right filter for your furnace.

By knowing the common filter sizes and types for furnaces, you can ensure that your furnace operates efficiently and effectively. Take the time to choose the right furnace filter and replace it regularly to keep your indoor air clean and healthy.

The Bottom Line

Replacing your furnace filter is an important part of maintaining your HVAC system to keep it running smoothly and efficiently. Be on the lookout for signs like poor indoor air quality or increased energy bills, and make sure to replace your filter regularly based on its size and your household's needs. If you're unsure about which filter size or type to use, don't hesitate to consult with a professional HVAC technician.

By taking proper care of your furnace filter, you can save money in the long run and breathe cleaner air. Don't neglect this crucial aspect of home maintenance!

Frequently Asked Question

It's important to know the size and type of furnace filter you need before replacing it. This is because different furnaces require different sizes of filters. Your brand of furnace may need an electrostatic or media filter of a particular size - so make sure to check your old filter for these details.


Replacing your filter regularly can save you money in the long run. It helps your HVAC system become more efficient, and also keeps the air quality high. So, what are the most common furnace filter sizes?


The most popular furnace filters come in the following dimensions: 10x20, 14x20, 16x24, 18x30, 12x12, 14x24, 16x25, 20x20, 12x20, 14x25, 18x18, 20x24, 12x24, 14x30, 18x20, 20x25, 12x30, 15x20, 18x24, 20x30, 12x36, 16x20, 18x25, 24x24 and 25x25. You can use your existing filter as a reference guide to find the perfect size for your furnace. The filter dimensions should be printed on its frame as length x width x height.


In conclusion, it's important to know your furnace filter size before you replace it. Doing so will improve your HVAC system's efficiency and save you money in the long run. Plus, a clean filter is key to keeping your air quality high.

When it comes to furnace filters, exact size matters. If you get a filter that is too small or too big, air will flow around it instead of through it, meaning not all of the air will be filtered. That's why it's essential to use the right size filter for your HVAC unit.


Here's what you need to know: the size of the air filter is typically listed in the big, bold font on the packaging, which is known as the nominal size. This is a rounded-up whole-number version of the actual size, which is written in the fine print on the filter's frame. That's usually 0.25'-0.5' smaller than the nominal size, and the actual measurements of the filter may vary slightly depending on the brand.


In some cases, less common sizes come true to size, meaning the nominal size is the same as the actual size. When that's the case, it's usually noted with “actual size” in parentheses on the filter's frame.


So, the verdict is in: the answer to the question 'Do furnace filters have to be exact size?' is a resounding yes! Be sure to get the right size air filter for your system to ensure it runs smoothly and that you reap all the benefits your filter has to offer.

Are you looking for the best furnace filter? Look no further! Our team of experts at This Old House Reviews have researched the top five furnace filters on Amazon to help you find the perfect one for your HVAC system. Plus, these products are available at local home centers or online retailers like Amazon.


A great furnace filter can make all the difference. It will keep your HVAC system running smoothly, potentially leading to lower electricity bills and better air quality. That's why we've taken the time to compile a list of the best furnace filters for you.


At the top of our list is the Filtrete furnace air filter. It promises to last up to three months and outperform filters made with fiberglass. Plus, it can capture 64% of airborne particles like pet dander and pollen. This filter also comes with instructions for easy installation on HVAC systems that require filters 20 by 25 by 1 inches in size.


Customers love this furnace filter. They find it easy to install, sturdy, and a great value. However, some customers have faced difficulties with Filtrete’s app.


When choosing a furnace filter, make sure to take into account its size, filtration level, and material. That way, you can get the best filter for your specific needs.

Changing or replacing your furnace filter is one of the best ways to maintain a healthy, efficient HVAC system. But you need to make sure that you're using the right filter for your system. Here's a step-by-step guide to help you pick the perfect one!


First, measure the dimensions of your existing filter. This will tell you the length, width, and depth you need. The easiest way to do this is to look at the existing filter and buy the same size.


Next, you need to choose the right MERV rating. The MERV scale ranges from 1-20 and measures the filter's effectiveness at catching particles in the air. The higher the value, the more effective the filter is at trapping particles, but it also means less airflow.


Now it's time to decide on the type of filter. There are many options available, so take some time to research the best type for your system.


Once you have everything you need, it's time to install the filter in your furnace/air handler slot. Remove the old filter to make room for the new one.


Finally, make sure to replace your filter regularly. If it clogs up with dust and particulate, it can reduce airflow and become ineffective.

Furnace air filters are essential for your heating system. You should replace your filter at least once every three months. So, how do you select the best furnace filter for your needs? Let us help you out!


Generally, furnace filters are made up of a cardboard frame, fiberglass filter, and metal mesh. These materials work together to strengthen the filter and protect your HVAC components from dust and debris. Plus, they also help improve the air quality in your home. Without a filter, your HVAC system could become dirty and its performance would suffer.


As air passes through the furnace filter, it traps and catches any contaminants. If you don't replace or clean your filter regularly, it can obstruct airflow and cause damage to your HVAC system. In most cases, you should change your furnace filters every three months. However, you may want to replace them more or less often depending on the situation.