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4 Inch Air Filters

We manufacture a wide variety of 4 inch air filters to fit your needs. Our products are guaranteed to fit your AC or furnace.
Simply choose the size you need below.

Available Air Filter Sizes and Types

Can't find your size? Click here for Custom Air Filters

What MERV Rating Should I Use?

MERV stands for Minimum Efficiency Reporting Value. The rating tells you how effectively it captures different particle sizes. It's not the only rating system, but it is the only consumer standard available. No matter what type of HVAC filters you use, if the MERV rating matches, you'll get the same filtration quality.

Major home improvement retailers have developed their own rating systems that are similar to MERV, but not standard across brands and styles. The other filter rating systems are Microparticle Performance Rating, or MPR (created by 3M) and Filter Performance Rating, (developed by Home Depot) or FPR.

A MERV rating of 8 through 13 is recommended for households and many businesses. A good place to start would be a MERV 8 if no one in the home has breathing issues.

Air filters that fall within the 8 to 13 range can remove pollen, mold spores, lead or household dust, cooking dust, auto or welding fumes, and other similar contaminants. These air filters can catch anywhere from 20 to 85% of all particles, so they are ideal for home or office. These remove most particles while still remaining cost-effective.

But for homes with pets, allergies, and asthma patients, it is recommended you use MERV 11 as these can tackle pet dander and dust mites. For homes with smokers, it’s best to use higher-rated filters, MERV 13. Anything less and you won't adequately filter the smoke from the air.

We offer filters in a variety of MERV ratings. We also offer carbon filters to help combat odors. We do this so you can get what best suits your needs. You should only pay for what you need.

Why Should I Use a 4 Inch Air Filter?

The furnace filters you use in your home make a huge difference in the air you breathe. Even with good outdoor air quality, the air in your home is still full of allergens and other indoor pollutants - especially if you're a pet owner or a smoker.

These can have higher MERV ratings than something smaller, like a 2-inch air filter. A 4-inch filter will typically start at a MERV 8 and can range up to 16. Anything higher than a 14 is typically reserved for laboratories, hospitals, or other healthcare facilities that need the cleanest air possible.

However, you will definitely want to stay on top of replacing your 4 inch AC filter. If these get clogged up, it can put extra stress on your air conditioner. If you start to notice your energy bill increase or reduced airflow, it’s time for a replacement. Stagnant air is a sign that you need a replacement since dirty filters are less effective.

While you can technically use higher than MERV 13 in your home, it's generally not recommended. Air filters that are rated to handle more than household dust, pollen, mold spores, smoke, pet dander, and dust mites force your home's HVAC system to work harder than it needs to. Ultimately, this translates to more wear and tear on your heating and cooling system.

Keeping your air filters clean is a major part of maintenance, but using the wrong filter can be just as harmful.

Subscribe and Save for Better Air Quality

A 4 inch furnace filter lasts anywhere from six to eight months on average. We recommend changing your air filters regularly for the best air quality. This ensures the air in your home is free of airborne particles like mold spores, pollen, household dust, and dust mites.

Get air filters delivered to your door right on time. With our delivery subscription, you never have to worry about forgetting when it’s time for a replacement.

Plus, you will save on prices when you subscribe to our delivery service. Just select how frequently you want air filters delivered. Orders with two or more filters get free shipping, helping you save even more on your purchase.

Questions about air filter sizes?


  • How do you measure an air filter size?

    An air filter’s size is described using three different measurements. The length, width, and depth of a filter are printed out in small numbers along the frame of the filter on the cardboard edge of a Filter King brand filter. But other filters may not have this information conveniently located, and you may need to find the measurements yourself. When doing so, check to see whether the filter is square or not. If it is not square, then the smallest-size side’s measurement goes first, followed by the next side, and then finally the depth measurement. 10x15x1 is a proper example of the correct size. From the actual sizes, round up the measurements to the nearest whole numbers when you order new air filters. This rounded measurement is referred to as the nominal size and is used to match the right filter to its fitting air filter slot. By using the nominal size, you can order a new air filter that slides in and out of place with ease.

  • What is the most common size furnace filter?

    Currently, the most common size furnace filters are 10x20. But should your system need custom sized air filters, note that we offer custom sizing ranging from 8 x 24 x 1 to 25 x 30 x 1. We even offer 3M furnace filters 20x25x1 in size.

  • What size do furnace filters come in?

    There are hundreds of variant sizes of furnace filters because air filters and furnace are both the same. The only difference between the two is location. Filter King offers hundreds of different filter sizes capable of use for several home systems, including your furnace.

  • Where is the air filter on an AC unit?

    Depending on your AC unit, the air filter slot may be located in a hard to find location. First, try checking the blower compartment or return air duct where the air is cleaned before going through the unit. The unit itself may have the air filter inserted in a specific location.

  • Can I run my AC without a filter?

    Yes, but it is not recommended that you do so. There are several issues that occur for an AC unit, your home air system, and the home itself when an air filter is not installed. Think of a filter as a gatekeeper (which really is), and its purpose is to protect both you and your HVAC system from dust and dirt, that if left unfiltered, can cause harm to both you and your HVAC unit in the long run.

  • What happens if the air filter is backwards?

    Air filters are built with a tight mesh weave that is designed to capture and absorb incoming particles. Air is brought through the porous side, and the mesh weaving allows it to flow in and out while being cleaned. When backwards, air has a harder time coming through, which means the system will require more energy to push it through, and thus affecting the quality of air filtration. When an air system is strained like this, it causes a rise in home energy billing and possible mechanical damage.

  • Will dirty air filter affect AC?

    Yes, over time dirty air filters will affect AC more and more. The longer a filter is left in a system, the dirtier it becomes, and the more pronounced the effects will be. There are many factors that determine how long an hvac filter can last such as the type of filter, material, home size and daily habits. The higher the FPR rating system (developed by Home Depot), the longer the filter lasts. MERV rating is another popular rating system used both locally and internationally.

  • What happens if your AC filter is dirty?

    When your air filter is dirty, the mesh wearing that it consists of becomes clogged and full of dirt and debris. When this happens, the air that is supposed to flow forward through the filter has a harder time passing into the air system. The system will use more energy to try and push the air forward, straining itself and raising your energy billing in the process. The air inside your home may also start becoming stagnant and dirt over time since fresh air is unable to come in.

  • Are air filters important?

    Yes, they are very important to any air system they are in. Air systems have no way of knowing whether the air they are bringing in is clean or dirty. Air filters are essential to making sure that any air brought in is cleaned before entering the system. Without filtration, the air coming in from outside may contain any number of dust, debris pollutants, and allergens.

  • What are the symptoms of a bad air filter?

    Reduced airflow and increasing power bills are the first signs to watch out for. With a broken or old filter, your HVAC system has to work much harder to keep your house cool.

    When an air filter is bad, that can mean that it is either dirty or broken. When dirty, the symptoms include the air inside of a home drying out or stagnating and dust particles filling the air. If the air filter is broken or not working, removal ofparticles such as pollen, dust, mold, dust mites, bacteria, pet dander, smoke, mold spores, and viruses is limited, which means there is lack of cleaner air in the house.

  • How much is an air filter for House?

    The price of a single Filter King brand air filter varies depending on its measurements. However, the price falls when you buy multiple filters per order. Orders of two or more filters are also shipped for free.

  • What MERV rating should I use in my home?

    MERV ratin 8-13 is recommended for households. A good place to start would be at MERV of 8 if no one in the home has breathing issues. But for homes with pets, allergies and asthma patients, it is recommended you use MERV of 11. For home with smokers, its best to use a higher rated quality air filter in this category which is MERV 13. To learn more about MERV rating, visit this article we've put together.

  • How many air filters does a house have?

    This is entirely dependant on your home and the kind of AC system it has. Consult the homeowner’s guide for your home air system to understand how many air filters your home has and in what sizes.

  • Which should I buy, a disposable air filter or washable filter?

    Washable air filters may seem like an attractive option at a glance. There a varied opinions about the effectiveness of washable ac/furnace filters, but one thing is clear: the longer one uses a washable air filter, the less effective they become with removing smaller particles. Our recommendation? For guaranteed high indoor air quality, it's better to stick to disposable air filters.

  • What should I look for in a home filter?

    The three most important things to consider when selecting the correct filter for your home include, filter size, material and MERV rating and price. Here at Filter King, we're able to provide a wide variety of filters for your home and business with the best MERV rating and the best price.