Choosing the Right Furnace Filter Sizes for Outdoor Furnaces: Everything You Need to Know!

Are you looking for the right furnace filter sizes for your outdoor furnace? If so, then look no further! Choosing the correct furnace filter size is essential to keeping your outdoor furnace running efficiently and effectively. With so many options available in the market, how can you make the best choice?

In this article, we break down everything you need to know to make an informed decision. From understanding the importance of furnace filters to the various types available, we’ve got you covered. We’ll also walk you through how to choose the right filter size for your specific furnace and outdoor space.

No matter what type of furnace you have, whether it’s residential or industrial, this article offers valuable insights and tips to optimize your furnace’s performance. So, if you want to make sure your furnace is running at its best, keep on reading!

The Importance of Furnace Filters

When it comes to the overall health and efficiency of your heating system, furnace filters are essential. Not only do they help keep the air in your home clean and free of harmful pollutants, but they also protect your HVAC system from damage.

Furnace filters work by trapping airborne bacteria, dust, and allergens that would otherwise be circulating through your home. When these particles accumulate in your ductwork, they can cause issues like poor indoor air quality, clogged air ducts, and reduced energy efficiency.

Regularly replacing your furnace filter can help prevent these problems and keep your HVAC system running smoothly. A clean filter allows for proper airflow, which keeps your system from working harder than it needs to. This, in turn, can lower your energy bills and prolong the life of your HVAC system.

It's important to note that not all furnace filters are created equal. Make sure to choose a filter with a MERV (Minimum Efficiency Reporting Value) rating that's appropriate for your specific furnace and heating system. Consult with a professional if you're not sure which filter is right for you.

In conclusion, the importance of furnace filters cannot be overstated. They are a crucial component of any HVAC system, working diligently to protect your respiratory health and your heating system's efficiency.

Types of Furnace Filters

When it comes to choosing a furnace filter, there are several options to consider. Here are the four main types of filters:

1. Disposable Fiberglass Filters

These are the most common and affordable type of furnace filter. They are made of thin fiberglass material and designed to catch large particles like dust and debris. However, they do not catch smaller particles like pollen or pet dander. They need to be replaced every month or so, depending on usage.

2. Pleated Filters

Pleated filters are made of polyester or cotton material folded in pleats to increase surface area. They can trap smaller particles than disposable filters, making them a better choice for allergy sufferers. They also last longer, up to three months, and are more efficient at capturing pollutants.

3. Electrostatic Filters

Electrostatic filters use a self-charging electrostatic charge to attract and trap airborne particles. They are highly efficient and can capture particles as small as 0.3 microns. They are also washable and reusable, making them a cost-effective option. However, they may require more maintenance to maintain their efficiency.

4. HEPA Filters

HEPA (High-Efficiency Particulate Air) filters are the most efficient type of furnace filter, capturing up to 99.97% of airborne particles. They are made of dense fiberglass and pleated to increase surface area. However, they are also the most expensive type of filter and may require modifications to your furnace system to work efficiently.

Ultimately, the choice of furnace filter depends on your specific needs and preferences. Consider factors such as air quality, family allergies, and the size of your furnace before selecting a filter type. Consult with a professional if you're unsure which type of filter is best for you.

Factors to Consider when Choosing the Right Filter Size

Existing Filter Dimensions: The easiest way to find the right size filter for your furnace is to check the dimensions of your existing filter. Measure the length, width, and thickness of the current filter to ensure you purchase a replacement with the same measurements.

Furnace Size: The size of your furnace is another factor to consider when selecting the right filter size. Larger furnaces typically require larger filters to accommodate the increased airflow needs.

Airflow Requirements: Your heating system’s airflow requirements will also determine the size of filter you need. This information can usually be found in your furnace’s owner’s manual or by consulting with a HVAC professional.

By considering these factors, you can choose the correct size furnace filter to ensure optimal HVAC system performance and air quality in your home.

Steps to measure your existing filter and select the right size

It's important to measure your current furnace filter to ensure you choose the right replacement size. Here are the steps:

1. Turn off power to your furnace. Safety first! Make sure your furnace is turned off before you begin.

2. Remove the existing filter. Slide or gently pull out the existing filter from your furnace.

3. Measure the length, width, and depth of the filter. Use a measuring tape to measure the length, width, and depth of your current filter. Make sure to measure the filter itself and not the frame.

4. Choose a replacement filter with the same dimensions. Once you have the measurements, choose a replacement filter that matches the exact dimensions. This will ensure a snug fit and proper filtration.

5. Install the new filter, making sure it fits snugly. Carefully insert the new filter, making sure it is snugly in place. A proper fit will ensure efficient filtration, improved air quality, and help extend the life of your furnace.

By following these simple steps, you can ensure that you have the right furnace filter size for your outdoor furnace, and properly maintain a clean and healthy living environment.

Maintenance Tips: Keeping Your Furnace Filter in Top Condition

Regularly replacing your furnace filter is crucial in maintaining the optimal performance of your heating system. But it doesn't end there - here are a few more maintenance tips to keep your furnace filter in top shape:

1. Keep the Air Around Your Furnace Clean

The air around your furnace may accumulate dust, debris, and other particles that can clog your filter. Clean the area around your furnace regularly to prevent these particles from affecting your heating system's performance.

2. Use a Quality Filter

Investing in a high-quality furnace filter can improve the air quality in your home while increasing the efficiency of your heating system. Look for filters with a MERV rating between 9 and 12, as they provide an optimal balance between filtration and airflow.

3. Change Your Filters on Time

As mentioned earlier, replacing your furnace filter every 1-3 months, depending on the level of use and filter type, is essential. Skipping filter changes or replacing them late can cause clogs, which can, in turn, cause your heating system to work harder - reducing its lifespan, increasing energy bills, and affecting its heating efficiency.

4. Schedule Professional Maintenance

Scheduling regular professional maintenance for your heating system can help identify and address issues before they become serious. A professional technician can replace your furnace filter, clean and maintain your system, and identify and fix any problems that could reduce its efficiency.


Keeping your furnace filter in top condition means keeping your heating system running smoothly and efficiently. By following these simple tips, you can ensure that your filter is always working correctly, allowing you to enjoy comfortable temperatures while saving money on energy bills.


When it comes to choosing the right furnace filter sizes for outdoor furnaces, it’s important to take the time to consider your specific needs and preferences. The size of your furnace filter can impact the efficiency and effectiveness of your heating system, so it’s essential to get it right. Whether you opt for a disposable or reusable filter, make sure it’s the right size and MERV rating for your system. By doing so, you’ll be able to enjoy reliable, efficient, and comfortable heating throughout the winter months.

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.