The Ultimate Guide to Furnace Filter Sizes: What to Consider When Making Your Purchase

Are you tired of constantly replacing your furnace filter only to find out it doesn't fit? It may be time to consider the importance of finding the right furnace filter size. Not only can it save you time and money, but it also plays a crucial role in providing clean air and increasing the lifespan of your HVAC system. In this ultimate guide, we'll explore what to consider when making your furnace filter purchase.

Did you know that choosing the wrong filter size can even cause damage to your furnace? It can restrict airflow or allow air to bypass, leading to increased energy bills and potential breakdowns. That's why it's essential to know what size filter your furnace requires. Our guide will explain how to identify your current filter size and what to do if your furnace needs a non-standard size.

But it's not just about finding the right size. There are also different types of furnace filters to consider, from disposable fiberglass to reusable electrostatic filters. Our guide will break down the pros and cons of each type and help you determine which is best for your home and HVAC system. With our ultimate guide, you'll be able to confidently make the right furnace filter purchase for a cleaner, healthier, and more efficient home.

1. How to Identify the Correct Furnace Filter Size

Identifying the correct furnace filter size is crucial for keeping your heating and cooling system running smoothly. Here are some steps to identify the size you need:

1. Check the current filter size: The easiest way to identify the size of the furnace filter you need is to check the size of the current filter. The size is usually printed on the side of the filter, but if not, you can measure it using a ruler or tape measure.

2. Consult your furnace manual: If you don't have a current filter to reference, consult your furnace manual. It should provide information on the correct filter size for your specific make and model of furnace.

3. Measure the filter slot: If you can't find the filter size through the above methods, you can measure the filter slot in your furnace. Use a tape measure to measure the length, width, and depth of the slot, and then choose a filter that matches those dimensions.

4. Contact a professional: If you're still unsure about the correct filter size or don't feel comfortable doing it yourself, contact a professional HVAC technician. They can help identify the right size and install it properly.

Remember, using the wrong filter size can lead to decreased efficiency and increased wear and tear on your heating and cooling system. Take the time to identify the correct size for your furnace filter.

The Different Types of Furnace Filters Available

When it comes to selecting a furnace filter, you have a wide range of options to choose from. Here are some of the most popular types:

1. Fiberglass Filters

Fiberglass filters are the most commonly used type of filter. They are made of layered fiberglass and are designed to capture larger airborne particles such as dust and dirt. These filters are cheap and disposable, but they need to be replaced frequently.

2. Pleated Filters

Pleated filters are made of polyester or cotton paper and are designed to capture smaller particles. They have a larger surface area than fiberglass filters, which means they last longer and need to be replaced less frequently.

3. Electrostatic Filters

Electrostatic filters use an electric charge to attract and capture airborne particles. They are available in both disposable and washable options. Washable electrostatic filters can be reused for years, making them a more environmentally friendly option.

4. HEPA Filters

HEPA filters are the most effective type of filter and are designed to capture the smallest particles such as pollen, pet dander, and bacteria. They are available in both portable and furnace-mounted options, but they are more expensive than other types of filters.

When selecting your furnace filter, it is important to consider your specific needs and the needs of your family. Choosing the right filter can improve the air quality in your home and keep your furnace running smoothly.

The Pros and Cons of Disposable Fiberglass Filters

Disposable fiberglass filters are a popular choice for many homeowners because they are affordable and readily available. However, like any product, they have their pros and cons. Below are a few things to consider when deciding whether to purchase disposable fiberglass filters for your furnace:


  • Cost-effective: Disposable fiberglass filters are one of the most affordable options on the market. This makes them a good choice for those on a tight budget.
  • Easy to install: These filters are very easy to install and require no special tools or know-how. Simply slide them into your furnace's filter slot and you're done.
  • Good for simple air filtration: If you're simply looking to filter out larger particles like dust and pollen, disposable fiberglass filters are a good option. They can effectively capture particles as small as 20-30 microns.


  • Short lifespan: Disposable fiberglass filters typically only last for 1-3 months. This means that you'll need to replace them frequently, which can get expensive over time.
  • Poor filtration: While disposable fiberglass filters are good at capturing larger particles, they aren't as effective at trapping smaller particles like bacteria and viruses. This means they may not be the best choice for those with allergies or respiratory issues.
  • Eco-unfriendly: Disposable fiberglass filters are not environmentally friendly as they contribute to landfill waste. If you're looking to reduce your carbon footprint, you may want to consider a reusable or washable filter instead.

Overall, disposable fiberglass filters can be a good option for those looking for a cost-effective and simple air filtration solution. However, if you have specific air quality concerns, you may want to consider a higher-end filter with better filtration capabilities.

The Pros and Cons of Reusable Electrostatic Filters

When it comes to choosing a furnace filter, one option that is gaining popularity is reusable electrostatic filters. These filters are designed to be washed and reused, offering an eco-friendly alternative to disposable filters. However, as with any product, there are pros and cons to consider before making a purchase.


1. Cost-effective: While reusable electrostatic filters may have a higher upfront cost, they can save you money in the long run since they can be washed and used multiple times.

2. Eco-friendly: Since these filters are reusable, they reduce the amount of waste that ends up in landfills from disposable filters.

3. Effective at trapping debris: Electrostatic filters are designed to attract and trap particles that float in the air, such as pet dander, pollen, and dust. This can lead to improved air quality in your home.


1. Higher initial cost: As mentioned, reusable electrostatic filters typically have a higher upfront cost compared to disposable filters. This may not be feasible for everyone's budget.

2. Not as effective at trapping smaller particles: While electrostatic filters are effective at capturing larger particles in the air, they may not be as effective at trapping smaller particles, such as viruses or bacteria.

3. Washing can be challenging: Reusable filters require regular washing to maintain their effectiveness. This can be a challenge for some homeowners who may not have the time or desire to do so regularly.

Ultimately, whether to choose a reusable electrostatic filter or a disposable filter is a personal decision that should take into account budget, lifestyle, and home air quality needs. Consider the pros and cons carefully before making a purchase to find the best option for you.

What to do if you need a non-standard furnace filter size

If you have determined that your furnace requires a non-standard filter size, don't panic. There are still several options available to you. Here are some tips to help you find the filter you need:

1. Contact the manufacturer: Reach out to the manufacturer of your furnace and ask if they have any recommendations for non-standard filter sizes. They may have a list of compatible filters or be able to provide you with a custom filter.

2. Check with HVAC professionals: Consult with a licensed HVAC technician or contractor. They can help you identify the correct filter size and may be able to order a custom size or offer a solution based on your specific needs.

3. Try online: There are many online retailers that specialize in custom-sized furnace filters. A quick Google search should provide you with several options. Be sure to read reviews and verify the vendor's reputation before making a purchase.

4. Consider a filter adapter: If you are unable to find a filter in the size you need, a filter adapter may be an option. These adapters allow you to use a smaller or larger filter in your furnace while still maintaining proper airflow.

Remember, although finding a non-standard furnace filter size may require some extra effort and research, it is essential to keep your furnace running efficiently and prolong its lifespan. By following these tips, you can find a solution that fits your needs and budget.

Final Thoughts

Choosing the right furnace filter size may seem like a daunting task, but with the right information and considerations at hand, you can make an informed decision. Remember to factor in compatibility with your HVAC system, the level of filtration you require, and the frequency of replacements needed.

By investing in high-quality filters and changing them regularly, you will not only improve your indoor air quality but also prolong the lifespan of your HVAC system. With this ultimate guide, you can now confidently purchase furnace filters that suit your needs and enjoy a comfortable, healthier home for you and your loved ones!

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.