Can I Use a 1-Inch Filter Instead of 5-Inch?

Can I Use a 1-Inch Filter Instead of 5-Inch?

All forced air furnaces use a filter of some sort, where it forces air through the filter before entering the main body of the system, and most furnace and air conditioning systems share a filter. Many use 1-inch filters, but some use filters as thick as 5 inches. 

Can I use a 1-inch filter instead of 5-Inch? No, you should not use a 1-inch filter instead of a 5-inch filter. The reason you want to use the appropriately sized filter is straightforward: your furnace is designed to hold a certain height, length, and thickness of a filter for correct airflow.

Stores sell filters with those specific dimensions (i.e., 16x25x5) specially designed to fit snugly in your unit fora proper seal. If the filter does not fit snugly, the furnace will not function efficiently.

This article covers everything you need to know about air filters for your furnace system. We’ll also provide information on what size filter to use and why, the differences between pleated, HEPA, and other styles, and what thickness is best.

Can I Use a 1-Inch Filter Instead of 5-Inch?

You may wonder why this is even up for debate. Why would anyone want to use a thinner filter in their heating and cooling system?

Thicker filters universally tend to be more expensive than thinner filters, so some users wonder if they can make such cheaper options work in their system.

Unfortunately, a 1-inch filter will not work correctly in the place of a 5-inch filter. The filter needs to fit firmly in place, and there will be too much airflow around a filter that is just too thin.

Someone with a passion for do-it-yourself projects might suggest making a frame to hold a 1-inch filter in place. The problem with this idea is that it will not seal properly, and so particles will trickle through. 

Manufactures design 5-inch filters to capture more pollutants for a more extended period, so if your furnace operates with a thicker filter, it cannot have more dust and debris getting into its moving parts.

What is the Purpose of a 5-Inch Filter?

In the average furnace system, the air is pulled into the unit using return ducts in your home. The furnace then warms the air using a heat exchanger. 

A heat exchanger is a set of heated coils or tubes that wind back and forth inside your furnace. The air is then pushed through and out of the furnace by a blower fan. The blower fan then pushes the air into ducts that lead to the vents in each room of your home.

The air that enters each room in your home will cool as it hits colder air. The air is then pulled back into the return ducts and sent into the furnace to be warmed. This cycle repeats until your house hits the desired temperature.

The most important purpose of a furnace filter is to protect the internal blower fan from things like dust and hair. Debris such as dust and hair can get caught in the fan and slow it down, or even grind it to a halt. 

This process also serves to improve the indoor air quality in your home. Removing dust, hair, and other particles from the air will improve the air that you are breathing (source).

Other indoor air pollutants that can get caught in the filter and removed from your air include pollen, dust, mold, pet dander, and bacteria. Trapping these in the filter gives your home fresher, healthier air overall. 

If you are interested in an even cleaner ecosystem in your home, it is also important to keep up on the maintenance of any other air purifiers you may be using.

A clean air filter in your air purifier will avoid you needing to ask the question, “Why does my Honeywell Air Purifier smell?

Pollen, dust, mold, and pet dander are familiar sources of allergies. Having a filter that works properly will go a long way to reduce allergic reactions in your home (source). Simply stated, a proper furnace filter helps you breathe easier.

Image by OpenClipart via FreeSVG

What are the Types of Furnace Filter?

There are two main categories of furnace filters: mechanical and electrostatic. Mechanical filters trap particles on a porous surface, and electrostatics use an electric charge to attract the particles (source).

Mechanical filters 

Mechanical filters include fiberglass/synthetic, polyester, pleated, and HEPA.

The most commonly used furnace filter is the pleated filter, usually made of paper and polyester. These filters are inexpensive and do an excellent job. They will capture and eliminate 80 to 90% of particles 0.5 microns or larger.

Disposable fiberglass filters are incredibly inexpensive but are often not as high-quality as the other options. They will only sift out 80% of the larger particles, allowing the small pollutants 50 microns or smaller to enter your home. 

These filters are very energy-efficient because their design does not hinder the airflow in your system.

HEPA filters trap and eliminate 99% of particles 0.3 microns or larger in the air.

Still, they can leave your home at a disadvantage because they are not extremely energy-efficient. Because they slow down airflow so much, your system will have to work harder to push the air through (source).

Electrostatic filters 

Electrostatic filters are reusable and usually made with an aluminum or plastic frame. They attract the particles in the air with an electric charge and keep them attached to the surface. 

You will need to wash electrostatic filters regularly for them to function correctly, and they can be vacuumed or washed with water. Electrostatic filters last quite a bit longer than a disposable filter, as you can use them more than once.

Can I Use a Different Size Air Filter?

You might think that a filter with the right length and width will be fine because it will not move around much, but you must take thickness into account.

The design of your furnace requires it to have a specific amount of particles trapped by its filter. If your filter is not thick enough, it will not be catching the necessary dust and hair.

A furnace is only as efficient as its filter allows. If you are using an improper filter, your furnace will not be as efficient. If it has to force air through a filter that is too thick, or too dense, the efficiency will drop drastically.

Using a filter that is too small can be like not using a filter at all. The air will flow around the edges, allowing particles to pass by without a hitch.

If you think that stacking five 1-inch filters together will equate to a 5-inch filter, you are sorely mistaken. Because the designers intended 1-inch filters to work alone, stacking them together will make your furnace push air through a barely-penetrable wall. 

Stacking them will lessen your airflow and make your system extremely inefficient.

What Furnace Filter Do I Need?

The filter you should use is entirely dependent on your furnace. Each furnace will have differing height, length, and thickness specifications for use. Height and length for filters range from up to 30×30-inch down to 10×10-inch. Thickness ranges from 1-inch to 6-inch.

Your unit will have a label on it, indicating what size filter is needed. This label should also indicate if there are any other special considerations to be aware of.

Your unit might require HEPA filters. Every furnace is different, and it is essential to follow the specifications for your system.

MERV Ratings

Understanding a filter’s ability to remove particles from the air is an important part of choosing one.

The most common scale used to gauge filters is the Minimum Efficiency Reporting Value (MERV) rating. This system was created by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE).

The MERV scale grades filters on a range of 1-20. A filter with a MERV rating of 1 will filter the lowest number of particles from the air, and a filter with a MERV rating of 20 will filter out the most particles.

The average home furnace functions best with a filter rating between 7 and 13. If your filter has too high a MERV rating, it can be inefficient because the furnace has a more challenging time pushing the air through such a dense filter.

Always be sure to check with your furnace manufacturer to see if your unit has a maximum MERV rating.

Additional rating systems

While the MERV rating system is the most common, there are a couple of different systems used by sellers. If your furnace has a maximum MERV rating, you can find a conversion chart to compare how these systems relate to the MERV scale.


The American corporation 3M developed the Microparticle Performance Rating (MPR). This system rates filters on their ability to trap particles smaller than 1 micron. According to this system, the best filters have an MPR from 1,500 to 1,900 (source).


Home Depot created its own rating system called the Filter Performance Rating (FPR). This system rates filters on a scale of 1 to 10. A filter with a rating of 10 filters out the most particles.

How Long Do 5-inch Furnace Filters Last?

Each filter thickness has a different life span. 1-inch filters last from 1-3 months, while 5-inch filters can last up to 1 year (source). 

It is also essential to take into account where you live. In a warmer, humid climate, you might run your system more often than an arid temperate climate. The more often you use the system, the more the filter needs to be replaced.

It is important to remember that homes in which people smoke, use candles or fireplaces, or have pets, will need to change filters more frequently. Each of these creates more particles that get caught in your filter, making it dirty faster.

Another thing to take into consideration when changing your filter is the health of your household. If an individual has allergies or a medical condition, changing the filter sooner is better than later. 

In these situations, it is best to change your filter at the minimum suggested time. For a 5-inch filter, this is at the six-month mark.

A general rule of thumb when determining whether or not to change your filter is to check the surface of the existing filter. If the surface is covered in buildup and has turned gray — filters are typically white to start — then you should take a moment to change it. 

Excessive dust in your home or the unit taking an increasingly longer time to heat and cool are additional signs that the filter should be changed.

No matter how often you run your system, a thicker filter will last longer than their thinner counterparts. So, while thinner filters may be less expensive, they will not last as long. In the end, it is worth it to purchase the correct filter for your furnace.

Why is Changing Your Filter Important?

Changing the filter on your unit will extend its life. The most common reason for an untimely furnace breakdown is a dirty filter (source).

A dirt-clogged filter will hinder air from passing through, creating more work for the motor. An overworked motor will break down quickly, making it necessary for you to call a maintenance specialist.

In this situation, the best case is that your system will simply need repairs. If you have an older unit, not changing the filter often enough can do enough damage to require the purchase of an entirely new furnace.

Regular filter changes will show you a reduction in energy bills. When too many particles get trapped in the filter, it is harder for your system to push air through it. The more buildup it accumulates, the lower the efficiency drops.

A properly maintained furnace filter will help to improve the air quality in your home, and clean air is vital for your overall health. Breathing air free of pollutants boosts your immune system, improves your sleep, and reduces the chance of an asthma attack.

Changing your filter at the recommended time also helps reduce the severity of allergies (source).

Your furnace filter helps to keep allergens out of your home. If not properly maintained, those dust and pollen particles can make their way inside and make you miserable.

Having a fresh air filter improves the general cleanliness of your home. If your system is pumping out dirty air, those particles will settle on the surfaces in your home. A clean filter is a clean home.

Ensure Proper Installation

Improving the air quality in your home by changing the filter is quite an easy process. The first step is always to turn the furnace off. Then the existing filter simply slips out of the unit, and your new filter slides right into the vacant space. 

There are no tools required, just a simple removal and replacement. Be sure to insert the new filter in the proper direction, sliding it in backward could block the airflow in your unit. 

There will be markings that indicate which side of the filter should face the furnace. Do not forget to turn the furnace back on afterward.

It is also important to schedule regular maintenance of your unit. A trained professional will check for fire hazards and carbon monoxide, as well as check the electrical connections and thermostat calibration.

Advantages of a Thicker Filter

Furnace filters range in thickness from 1 inch to 6 inches. Thicker filters have more material to trap indoor air pollutants. They can filter out a higher percentage of particles than a thinner filter would.

Because they filter out more pollutants, thicker filters clean air better than thinner filters. A thicker filter tends to work more efficiently and lasts longer. A 5-inch filter can last up to a year, whereas a 1-inch filter only lasts up to 3 months.

Image by Marcus Cramer via Unsplash

Where to Find 5-inch Filters

While many retailers sell furnace filters, 5-inch filters are a bit rarer than their 1-inch counterparts. There are still several brands and options for you to choose from.

Home Depot

Home Depot sells Honeywell and True Blue options in 5-inch filters. These brands tend to be under $40 for single-filter packs.


Filtrete seems to be the only option at Lowes, and their 5-inch filters are under $80 for a two-pack.


An online retailer called FilterBuy has several options when it comes to 5-inch filters. They carry a variety of brands, including Honeywell, Maytag, and Trion. Depending on which brand you buy, you will typically spend under $60 for single-filter packs.

These are simply a few of the places that sell these larger filters. You may be able to find more options at other stores, such as Ace Hardware, or online.

Final Thoughts

Never try to use a 1-inch filter in place of a 5-inch filter. The designers intended your furnace to use a precise size, and you should always choose the filter with the correct proportions.

Using the wrong filter can cause problems with the flow of air, and ultimately cause damage to your unit.

The most commonly used type of filter is the polyester and pleated paper filter. It filters out a high percentage of particles, is not terribly expensive, and does not lessen the efficiency of your system. 

The proper filter will do a world of wonders in your home. It will heighten the efficiency of your furnace, as well as clean the air that you breathe. When you keep up on the maintenance of your heating and cooling system, you will live a healthier overall life.


I'm a Pharmacist and a passionate researcher into clean air and pure water for the home. I believe these 2 elements play a significant role in our health and overall wellbeing.

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