(707) 800-6287 |  Sonoma Napa and Marin Counties

Updated March 21 2022


When the hot or cold airstrikesair-filter-tips-and-tricks, it is always good to have a reliable HVAC system in your home or business space to cool things down or warm things up when necessary. During the installation of an HVAC system – especially if you plan to do some of it on your own – you will eventually start dealing with filters and wonder whether you can cut an air filter.

While some air filters will fit nicely without requiring any alteration, this might not always be the case, especially if you have ducts that deviate from standard designs. Therefore, you should always address the question of whether you can cut these filters to fit your ducts better and whether this will cause problems before you continue.

Before one can answer this kind of question, you need to investigate the purpose of an air filter, how they work, how one could cut it, and whether cutting it would change any properties that allow it to accomplish its job.


Understanding its Purpose Before You Cut an Air Filter

At its core, these filters act as a barrier between your home and impurities that would otherwise pass through your HVAC system and into your home. These impurities can include anything from dust to bacteria, depending on the environment around the HVAC system itself and how well you maintain your system. Another important job of these HVAC filters is to protect the HVAC system from intrusive particles that could damage it.

Therefore, it goes without saying that if these filters do not work properly, you potentially expose yourself and your HVAC system to impurities. The result could be anything from allergies flaring up to unwanted bacteria freely traveling around your home, and possibly even costly HVAC damages.


How an HVAC Air Filter Works

While there are different air filters (flat-panel, pleated, electrostatic, washable, high-efficiency particulate air), they all have the same purpose: to clean the air that passes through them. Now, even though they all aim to do the same thing, some accomplish this job in different ways than others.

More affordable air filters will commonly use material such as fiberglass that covers the framework of the filter, attempting to filter the particles that pass through. Keep in mind that more affordable comes with an additional price, being they do not filter as well as pricier options.

Other types of materials used range from screens of dense cotton or plastic fibers to electrostatically charged materials. At the top of the list, you will find HEPA filters. These filters deliver exceptional filter quality and are commonly found in hospitals or similar areas that require the cleanest air.

By now, we have established that there are many kinds of filters to use and, more importantly, that they can all cause problems when faulty, which brings us back to our original question: can you cut an air filter and still get full use out of it, or will it degrade the quality of the filter?


Answering the Question: Is it okay to cut an air filter to fit?

The first thing you need to consider is the type of air filter you plan to cut. The reason for this is because some of these filters – especially the more expensive options – can lose much of their structural integrity if cut without experience. When this happens, the filter can perform more poorly than intended, leading to damage to your HVAC system or unwanted particles in your home or business.

The second thing you need to consider is the instructions from the manufacturer itself. If the manufacturer states that you can cut the filters to fit as you please, it is obviously more recommended than if the manufacturer warns against it.

Some manufacturers can even customize the filters for you to fit perfectly when you or your HVAC team puts everything together.

Simply put, yes, you can cut an air filter if you know what you are doing, and if the filters you use will not become too weak from the cutting.


Make Sure You Choose a Reliable HVAC Team

The best thing you can do is work with a team you can trust when choosing your high-performance HVAC system, which HVAC control system you should get, buying reliable products, and maintaining your HVAC system and its filters with regular HVAC cleaning services. The team you choose will ultimately dictate how flexible your system is, how fine-tuned it is for your property, and whether you even need to cut your air filters in the first place.

We recommend keeping an open line of communications with your HVAC team so that your systems can run optimally around the clock. While a good quality filter can do much for your HVAC system and your home, you should never underestimate the importance of HVAC maintenance.

If you ever have any further questions, such as how to cut an air filter, or need a team that can help you set up, install, or decide on products, simply give us a call, and we can help you immediately.


The air filter is one of the most important parts of your HVAC system, but it’s often the most overlooked. Making sure you have the right filter installed in your air conditioner is a vital part of keeping it up and running smoothly. However, many homeowners don’t really pay attention to the filter they’re using. After all, once you’ve spent a few thousand dollars to install an HVAC system in your home, who has the mental energy to pick out a filter as well?

That’s why we put together this post to help you get started. There are a ton of factors that go into the filter selection process, so it’s important to understand what you’re doing when you go in. Picking the right filter can extend your air conditioner’s life while making sure you and your family are enjoying pure, clean air for years to come.

Why Air Filtration is Important

There are two main reasons why the air filter is such an important part of your air conditioner. The first is pretty obvious: the better the filter, the higher the air quality inside your home. Air quality might not be the most noticeable thing in your house, but it can have a significant effect on your health, especially if anyone in your family has a history of asthma, allergies, or other respiratory conditions. This is doubly true once spring comes along and the air is filled with pollen.

An air filter can also protect you from other, more dangerous pollutants. One of the most troubling air contaminants is mold, which travels through the air in spores. If these spores make it inside your house, they can cause mold and mildew to grow inside your ducts, which is a serious problem. Mold in your HVAC system can also create a whole plethora of health problems for you and your family if the spores are blown into the air.

If you find yourself experiencing symptoms like coughing, sneezing, and other cold or flu symptoms, especially when the air conditioner is turned on, you might have a problem with the air quality. Chances are, you’re going to have to replace the filter with a new one. If the symptoms persist, it might be time to have your ducts cleaned in case there’s mold growing in there.

A proper air filter can also make a significant difference in the operation of your HVAC system. If you leave a filter in for too long, or if it’s not the right kind of filter, it can get clogged up with dirt, dust, and other contaminants. Not only does this present a problem for your indoor air quality, but it can also impede airflow from the air conditioner into the vents. If the system can’t get enough air through the vents to cool down the rooms of your house, that forces the air conditioner to work harder. This means it’ll require more power, driving up your monthly electricity bills.

When the air conditioner is forced to stay on for longer, that also means more wear and tear on the moving parts inside the unit. Air conditioners have a ton of parts inside, including a few motors that power the fans, and working harder to push air through a dirty filter will cause strain to all those parts. Even with regular maintenance, leaving a dirty filter inside your air conditioner can cost you a pretty penny in repair bills and even shorten the lifespan of the unit. It’s a lot cheaper, in the long run, to replace the filter regularly instead of having to replace the entire air conditioner.

Types of Air Filters

Air filters come in a ton of different varieties, each with different price points and capabilities. It’s worth looking into each kind before deciding on which one will best serve your needs. We also recommend checking the instructional manual for your air conditioner or talking to your HVAC technician when the system is first being installed to see which filter is best for your unit.

Flat-Panel Air Filters

Traditional flat-panel air filters are the least expensive kind, but they’re also the least effective. These filters are typically made of fiberglass or other fiber materials stretched across a plastic framework. They do have a few advantages, mainly their low cost and the ease of installation. They’re also disposable, so you don’t have to worry about washing them and putting them back. However, flat-panel filters are usually relatively low quality, which can allow some particles to get through. Generally, we don’t recommend using flat-panel filters in a central air conditioner system, especially if you’re concerned about the air quality in your area.

Pleated Air Filters

Pleated filters are pretty similar to the usual flat-panel ones, but with a few key differences. They use pleated fabric, usually plastic fiber or cotton, stretched out over frames similar to the ones used in flat-panel filters. However, the greater surface area of the pleated filters allows them to capture more particles than their non-pleated counterparts. Though pleated filters are slightly more expensive than the standard flat-panel ones, they’re much more effective and are recommended for use in central HVAC systems. Pleated filters are also disposable, so you’ll have to buy new ones pretty regularly.

Washable Air Filters

As the name suggests, washable air filters are reusable versions of regular flat-panel or pleated filters. They’re more expensive than the disposable filters, but they tend to pay for themselves since they can just be hosed down or vacuumed every once in a while instead of having to be replaced entirely. This also makes them a more eco-friendly option for homeowners who want to be as environmentally conscious as possible. Even these reusable filters don’t last forever though, so you will have to eventually buy a new one after a few years of use.

Electrostatic Air Filters

An electrostatic air filter is a filter that has been charged with static electricity, the idea being that the electricity will trap small particles like mold and bacteria and hold it in place, improving the efficacy of the filter. Both pleated and flat-panel filters can be electrostatic, and they can be either washable or disposable. It’s worth noting, however, that reusable electrostatic air filters do eventually lose their charge as you wash them, so they have a shorter lifespan than the regular washable ones. Some studies have been performed that show electrostatic air filters trap more dust and other particles than regular non-charged filters, but more research is required to determine how effective they really are.

HEPA Filters

HEPA, which stands for high-efficiency particulate air, is a title given to any air filters that perform above a certain threshold. You can think of HEPA less as a category by itself and more as a stamp of approval from the Department of Energy. In order to be considered a HEPA filter, an air filter has to be able to remove at least 99.97% of all particles larger than 0.3 microns. That means HEPA air filters will always be the most effective method of preserving the quality of your air. They can be flat-panel or pleated, as well as either disposable or reusable, as long as they match that standard.

HEPA filters are most often used in large commercial buildings that require clean air, like hospitals. However, they can also be purchased for use in residential HVAC systems, and are by far the best kind of filters available. It’s worth noting HEPA filters can be too thick for some HVAC systems, so you should check the manual or ask your installation technician before buying one for your home. If the unit doesn’t have enough power, the filter can actually block airflow and reduce the efficiency of the system.

Beyond the HEPA category, air filters are further sorted by their Minimum Efficiency Reporting Value, or MERV rating. MERV is a scale that runs from 1 to 20 and was developed by the the American Society of Heating, Refrigerating and Air-Conditioning Engineers to measure the ability of a filter to remove particles from the air. We’ll talk a little more about MERV and selecting an air filter later on in this post.

Air Filters vs Air Purifiers

An air filter is a requirement for any HVAC system, no matter the size. Even the smallest window-mounted air conditioner unit will have a filter inside – you have to clean or replace those too, by the way. However, if you’re especially concerned about the quality of your air, you might choose to add an air purifier to your system. While the filter is an essential component built-in to the HVAC unit itself, an air purifier is a separate unit that you can set up alongside the rest of the system. There are a wide range of air purifiers available, and some are more effective than others.

Extended Media Purifiers

An extended media purifier is essentially a box full of filters that can be installed in your ducts to provide an extra layer of filtration once the air has left the unit. These units require a professional to install in your ducts, but only have to replaced afterwards about once a year. If you’re especially concerned about the quality of your indoor air but you’re not looking to break the bank with a more technologically-advanced purifier, an extended media filter should do the job just fine without interfering with the regular HVAC operation.

Electrostatic Precipitators

These high-tech electric purifiers use static electricity to filter particles from the air, like a much more advanced version of an electrostatic filter. Like the extended media purifiers, precipitators are installed inside your ducts. As air passes through the purifier, it’s zapped by a current that charges any particles that made it through the regular filter. Oppositely-charged plates on the other side of the unit then capture the charged particles, removing them from the air.

If you’re concerned about germs, you can have an ultraviolet purifier installed in the electrostatic precipitator. This device uses UV radiation to kill bacteria and viruses that pass through it in the air. UV purifiers are often used in hospitals to protect patients with tuberculosis and other diseases that make them vulnerable to germs.

Electrostatic precipitators cost more than other purifiers, but they never have to be replaced. However, you should clean the collection plates with soap and water every few months to get rid of all the particles trapped there. It’s worth noting that the process of charging the particles in the air can sometimes create small amounts of ozone through ionization. Ozone can be a lung irritant, so someone with a sensitive respiratory system should be careful with electrostatic precipitators.

Do I Need an Air Purifier?

The truth is, the vast majority of homes have absolutely no need for an air purifier in addition to the usual air filters. That’s especially true if you have a HEPA filter installed in your HVAC unit, since these filters actually outperform even dedicated air purifiers when it comes to removing particles from the air. However, there’s also not much of a downside to adding a purifier, so if it makes you feel better about the quality of your air, you might as well buy one.

It’s also worth keeping a purifier in mind if your unit can’t handle a full HEPA filter and somebody in your household has the potential for respiratory issues. While a standard pleated or flat-panel filter will usually do just fine, it’s better to be safe than sorry, and peace of mind is always an important factor to consider when making these decisions.

At the moment, there have been no controlled studies performed on whether or not a purifier is medically helpful for people with respiratory sensitivities, so the jury is still out. However, if you find that a filter isn’t doing enough for your allergic or asthmatic symptoms, it’s worth giving a dedicated purifier a try.

Choosing an Air Filter

When deciding on an air filter for your HVAC system, there are a few different things you should consider. First things first, you need to find out the size of the filter your unit requires. This might seem like a small detail, but cutting an air filter down to a smaller size can sometimes damage the structural integrity of the filter. This is especially true for higher-end filters. The filter size should be listed in the instructional manual that came with your HVAC unit. While you’re there, you should also check to see if there’s a recommended MERV rating. Some HVAC units can’t push air through HEPA filters and others with a high MERV, so make sure you’re following the manufacturer’s recommendations to avoid affecting the efficiency of the system.

MERV ratings measure the filter’s ability to remove particles from the air. It’s based on the size of the particles that the filter removes as well as how effectively it does so. MERV ratings go from 1 to 20, but you most likely won’t need something all the way on the high end of that scale.

Filters with MERV ratings of 1-4 are generally considered subpar for use in an HVAC system. These filters can block larger particles like dust, pollen, and carpet fibers, but not a whole lot else. You’ll typically see filters with a MERV of under 4 in residential furnaces, window-mounted air conditioning units, or as a pre-filter in commercial units that need multiple filters. Regular flat-panel fiberglass filters will usually be around this level, which is why they’re not usually recommended for a central HVAC system. However, if you’re more focused on energy-efficiency than the air quality, these low-end filters will allow more airflow than others, so it’s a tradeoff.

Most standard HVAC systems will recommend a filter with a MERV rating between 5 and 8. These filters can block dust and pollen just as well as the previous ones, but they’ll also catch smaller particles like dust lint and mold spores. They’re pretty common, as most residential buildings and non-specialized commercial buildings have air filters at this range. They also provide a good balance between air quality and the efficiency of the system. Unless you have concerns about respiratory conditions or a sensitivity to poor air quality, there’s very rarely a need to go above MERV 8. Most of the filters you see in this range will be pleated fabric or plastic.

MERV 9-12 are usually the highest quality air filters that you’ll find in regular residential buildings. They’ll block dust, mold, pollen, and finer dust like coal or lead, which is helpful if you live in an area with poor air quality. If you have sensitive lungs or are asthmatic, you may want to consider a filter in this range, although it will reduce the efficiency of your HVAC system. At the higher end of this range, like MERV 11 or 12, the filter will also capture larger bacteria like legionella, providing an extra later of medical protection. For this reason, most hospital laboratories and waiting areas will have filters between MERV 9 and 12.

Once you reach MERV ratings between 13 and 16, you’re firmly in the range of medical grade air filters. These filters are used in hospitals because they’re fine enough to capture most viruses and bacteria, preventing disease from spreading. In recent years, many businesses have installed filters with a MERV of 13 or higher because it can block the covid-19 virus from spreading through the HVAC system. However, many residential HVAC units can’t handle filters this fine without potentially damaging the evaporator coil or other internal parts. Make sure to refer to the instruction manual before purchasing a medical grade filter.

Filters with a MERV rating of 17 or above are considered to be HEPA filters. A HEPA filter can remove just about anything from the air, right down to smoke, odors, and microscopic allergens. HEPA filters can block anything bigger than 0.3 microns with 99.97% efficacy, making them about 30 times as fine as a standard fiberglass filter. However, it may be difficult to find a residential HVAC system that can handle a filter like this – at least, for now. After covid-19, many HVAC companies have been hard at work designing systems that can handle HEPA filters so they can remove viruses and bacteria from the air as it cycles. It’s possible that, within a few years, you could buy an air conditioner with a HEPA filter for your home relatively inexpensively.

Call a Professional Today

Although it might sound exhausting to dive into the world of air filters right on the heels of the research you did to pick out your air conditioner or furnace, it’s extremely important to make sure you have the right one. We’ve gone over some factors to consider in this post, but ultimately everyone’s situation is specific enough that we recommend getting in touch with a trusted HVAC company so they can analyze your house, the quality of the air outside your home, and other personal factors that might be relevant. This is the best way to make sure that you’re getting a filter that suits all your family’s needs.

If you live in Sonoma, Napa, or Marin Counties, we at Valley Comfort Heating and Air would love to be that trusted HVAC partner for you. We have years of experience with both residential and commercial HVAC systems, and we know the air quality needs of the area inside and out. If you’re interested in having a chat or getting help with your HVAC system, you can contact us through our website or give us a call at (707) 755-6951. We’re open from 7:30 am to 5:00 pm, Monday through Friday.