Every HVAC system has an air filter. Ensuring your HVAC air filter is clean is essential to ensure your HVAC system works efficiently, if at all. It can improve the indoor air quality (IAQ) of your home and helps reduce ownership costs through reduced energy bills and less frequent repairs and maintenance.
Replacing your HVAC air filter is simple, and this guide will cover exactly how to change your HVAC filter, including questions such as how to know what size filter you need? What type of filter efficiency rating should you buy? And how often should you replace your filter?
With a family history in HVAC of over 35 years, I can confidently say that regularly replacing your HVAC air filter is the simplest, most cost-effective way to maintain your HVAC system.
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Why you should replace your HVAC filters regularly
Replacing air filters leads to better indoor air quality
It's easy to forget to change your air filters. You can pop them in and let them do their job. However, leaving your air filters in too long will taint your home's air quality. The air circulating in the house contains pollutants, such as gases, chemicals, and other particles. As your HVAC system works, these particles restrict the airflow, reducing the air filter's effectiveness.
Poor air quality can aggravate symptoms of severe respiratory or skin allergies. Dust, dirt, mold, and other allergens can irritate the eyes and cause fatigue. Prolonged exposure to poor air quality can lead to other long-term health complications.
Regularly changing your air filters will improve the performance of your system and will effectively remove more harmful particles from the air in your home, improving IAQ.
Replacing air filters saves you money
Leaving a dirty air filter in your HVAC system will raise your energy bill. As your HVAC system works, air passes through it. A dirty filter will restrict the airflow, causing your blower fan motor to work harder and consume more energy.
Replacing your air filter more frequently will not only help your HVAC system run more efficiently and lower energy costs. It will also increase the longevity of your HVAC system and reduce repairs. A clean filter will reduce the strain on the blower fan motor, reducing the chances of motor failure and high static pressure problems.
Replacing air filters is more sustainable
Since clean filters allow air to flow more effectively through the HVAC system, the system will consume less energy and is more sustainable, especially on hot summer days when there is a lot of strain on the electricity grid.
Additionally, replacing air filters as opposed to using washable filters is also better for the environment. Most people wash washable filters into a sink or lawn, which can contaminate the soil and water supply locally.
Using disposable air filters is more sustainable and is better for your health. They filter out contaminants more effectively and cause less harm when disposed of properly.
How often should you replace HVAC air filters
Now that we know the importance of replacing air filters let's review how often you should do it. Generally, a filter should be replaced whenever it gets dirty and causes airflow restrictions. As a general rule of thumb, one-inch filters last about 2-3 months, and five-inch filters last between 6-12 months.
However, this is a big generalization because how fast a filter gets dirty depends on how much air flows through it (for how long the fan is on) and the indoor air quality (how many particles the filter needs to catch). You can buy a new filter and barely run your system, and your filter will last longer, or you can run your fan all the time to improve IAQ through filtration, and your filter will have a shorter lifetime.
Therefore we recommend checking your air filter monthly to determine when you should replace your air filter. Or you could invest in a smart thermostat that can notify you when to replace your filter based on how often your fan is on.
What does a dirty air filter look like?
An HVAC filter will become discolored as it removes particles from the air. However, often the conditions in the home make it appear that the filter is dirtier than it is because of smoke in the house from cooking, candles, or smoking.
A new filter will be white, and over time it becomes gray.
Below are a few images of filters that are dirty at different levels. The first is a clean, brand-new filter, the second and third filters are dirty and should be changed, and the fourth and fifth are highly restricted filters.
Your filter should never resemble the fourth or fifth in any way. Significant restrictions cause issues such as blower wheel (fan) motor failures and high static pressure.
Signs of a dirty air filter include a noisy system and improper heating or cooling.
Where is the HVAC filter located
The HVAC filter is located in one of two places: on the air handling unit (gas furnace or central air handling system) near the blower fan or on the return grille (vent) on the ceiling or wall.
Start by looking for the return grille (vent). The return grille is the one that sucks the air into the HVAC system as opposed to blowing it out into your home. It should be easy to locate as it is typically much larger than the supply grilles (vents). To ensure a vent is a supply or return, you can turn on the HVAC system and feel if the air is sucked in or blown out. We are looking for the one that is sucking in.
Once the return grille has been found, see if a filter is located at the entrance of the grille. It should be easily visible.
Here is what it should look like when there is a filter at the return grille.
And here is what it should look like when there is no filter at the return grille.
If there is no filter at the return grille, then the filter is located near the blower wheel (fan) at the gas furnace or air handling unit. The air handling unit can be found in a closet in the home, the garage, an attic, a basement, or a crawlspace and may be harder to reach.
If you are attempting to replace the filter yourself, you may need a ladder to reach the attic, and consider wearing old clothing as it may get soiled from dust, dirt, or insulation.
If it's in a crawlspace or attic, it may be harder to reach, and you will need to get down and dirty to get the job done.
In rare cases, there will be no filter if the previous owners did not have them in place. If that is the case, consider getting an HVAC system cleaning, as the dust, dirt, and debris build-up can negatively affect the system performance and indoor air quality.
Determining your HVAC filters size
When replacing the air filter, buy the same size filter as before. The HVAC filter size is determined when the HVAC system is installed or if any modifications are made to the ducting system. The HVAC pro determines the initial size to meet the system airflow requirements.
If you are installing a new system, you may have a choice of how thick your filter is. The most common in residential HVAC systems are one-inch or five-inch thick filters. We always recommend opting for the five-inch filter.
Yes, five-inch filters are more expensive. However, five-inch filters have a greater surface area for air to flow, allowing them to last longer, and improve system performance.
If you are unsure what size filter you need when replacing an existing filter, you can check on the old filter itself. All filters are labeled with the size on the sides of them. If you cannot see the print clearly, you can measure the dimensions with a tape measure.
There should be no r to change the filter size. Each filter sits in a housing that ensures no air flows around the filter. If you purchase a filter that is too small, air will be able to flow easily around the filter, and if the filter is too big, it won't fit in the housing.
In rare cases, you may find a forced filter or one too small for the housing. If that is the case, you should contact an HVAC pro to determine the correct filter size.
Types of Air Filters for HVAC
There are many types of HVAC air filters available on the market. Usually, when you install a new system, how it is installed or the type of system you have determines what type of filtration you have. Sometimes, you can swap the filter type as long as it is compatible with the filter housing. If you are considering changing your HVAC systems filter type, consult with an HVAC professional.
Below we will cover different air filter types and the pros and cons of each one.
Washable, metal, and electrostatic HVAC air filters
There are a few types of metal washable HVAC filters. The most common are basic or pre-filtration washable filters and electrostatic washable HVAC filters. The pre-filters trap large particles, removing them from the airflow and preventing large dust and debris from causing the internal components of an HVAC system to get dirty. And electrostatic filters use an electric charge to capture and attract smaller particles removing them from the airflow.
Metal filters need to be washed frequently to be effective. The pre-filter isn't good at removing small particles from the airflow, and the electrostatic part of the filter reaches its full capacity fast. It is recommended to clean them at least once a month.
We do not often recommend electrostatic or "metal washable" filters for two main reasons. The first is that most electrostatic filters produce a small amount of ozone, a known lung irritant. And second is because for them to be effective, they need to be cleaned often, which can be an inconvenience for many people, especially if the HVAC filter is located in a hard-to-reach place such as an attic or crawlspace.
Fiberglass HVAC air filters
Fiberglass filters are also a basic form of filtration for HVAC systems. They often come in very low MERV ratings and are mostly used to protect the internal components of the HVAC system from getting dirty. Fiberglass HVAC filters are not effective in improving indoor air quality.
Fiberglass air filters are disposable and often have a lifespan of about 1 to 3 months, depending on the indoor air quality and how often the HVAC system is turned on.
Although some companies produce fiberglass HVAC filters with electrostatic capabilities, they incorporate a metal grille between the fiberglass fibers and use a dedicated electronically charged return grille (vent). To electrostatically charge the filter.
This is a step up from the traditional fiberglass filter; however, as stated above, some electrostatic filters produce a small level of ozone, so you need to be aware and be sure to ask your HVAC pro if the type they offer produces ozone or not.
Pleated HVAC air filters are the most common filter type in HVAC systems. Pleated filters are the common ones that are folded into an accordion-looking pattern. Pleated filters are the filters that are rated in the MERV, FPR, and MPR rating systems.
Pleated filters can be 1, 2, 4, or 5 inches thick. The one and 5-inch options are typically used in residential applications, and the 2 and 4-inch options are typically used in commercial applications.
Because of the accordion shape, the greater the thickness of the filter, the more surface the filter has to trap particles, and the longer the filter's lifespan. The 1 and 2-inch pleated filters typically last about 2 to 4 months before needing to be replaced, and the 4 and 5-inch filters need to be replaced every 6 to 12 months.
Pleated HVAC air filters using the MERV, FPR, and MPR rating systems are typically synthetic polyester. However, the material and methods used to construct the material can vary by manufacturer. We always recommend purchasing authentic manufacturer-approved filters. Most after-market filters are not constructed correctly, which can increase the static pressure of the HVAC system. Authentic filters can achieve the rated efficiency rating while still allowing good airflow in the HVAC system, which can help reduce static pressure problems.
Activated carbon and charcoal HVAC air filters
Activated carbon or charcoal is often added to pleated HVAC filters. The active carbon is very porous and can trap harmful pollutants such as VOCs and other gases. Activated carbon filters are good at removing bad odors from the home.
Activated carbon become popularized by many of the small portable air purifiers on the market however the benefits of activated carbon filters can be maximized when used in a central HVAC system. Because a central HVAC system moves air throughout the home, the filter can be utilized more effectively.
Choosing a filter efficiency rating (MERV vs. FPR vs. MPR)
The three standard filter efficiency rating systems are MERV, FPR, and MPR. The MERV rating system is considered the most common and international standard. However, some companies have developed other methods to rate their filters.
We can look at it in the same way as the metric system vs. the empirical approach—different number systems to calculate how efficient a filter is at filtering out air particles.
MERV - Minimum efficiency reporting value
The MERV rating system is considered the most popular rating system in the industry. MERV ratings range from 1-16, where one is the lowest, filtering out the least amount of particles, and 16 is the highest, filtering out the most.
The MERV rating of a filter is determined by its ability to filter out particles sized between 0.3 and 10 microns. For reference, a strand of hair is about 70 microns.
The MERV rating of a filter is calculated through a test that checks how efficiently it removes particles of different sizes. Larger particles between 3.0 to 10.0 microns, medium-sized particles between 1.0 to 3.0 microns, and small particles between 0.3 to 1.0 microns.
Each rated filter needs to filter out a certain percentage of particles of various sizes.
Below you can find a side-by-side comparison between MERV efficiency ratings based on particles of various sizes. A detailed list of particle sizes can be found here.
MERV 8 - filters can filter out more than 70% of particles between 3.0-10.0 microns and more than 20% of the particles between 1.0-3.0 microns.
MERV 10 - filters can filter out more than 80% of particles between 3.0-10.0 microns and more than 50% between 1.0-3.0 microns.
MERV 11 - filters can filter out more than 85% of particles between 3.0-10.0 microns, more than 65% between 1.0-3.0 microns, and more than 20% between 0.3-1.0 microns.
MERV 13 - filters can filter out more than 90% of particles between 3.0-10.0 microns, more than 85% between 1.0-3.0 microns, and more than 50% between 0.3-1.0 microns.
MERV 16 - filters can filter out more than 95% of particles between 3.0-10.0 microns, more than 95% between 1.0-3.0 microns, and more than 95% between 0.3-1.0 microns.
When considering what MERV rating to buy, remember that the higher the rating, the more effective it is at removing smaller particles. In many states, the minimum required MERV rating on new HVAC systems is MERV 13.
FPR - Filter performance rating
The FPR rating system, developed by Home Depot, again gives us the filter's efficiency rating.
The FPR rating of a filter is calculated by the filter's ability to capture large and small particles and how much added weight the filter gains from the particle build-up through the filter lifetime.
The FPR uses a weighted average to calculate the score, ranking on a scale of one to ten, with ten being the highest. Large particles have a 60% weight, small particles have a 30% weight, and the added weight to the filter is 10% in the total calculation.
FPR filters come in four efficiency ratings, 4 - good, 7 - better, 9 - best, and 10 - premium. What you choose depends on how effective you want your filtration to be.
FPR Rating 4 - filters out large particles like household dust and lint, dust mites, pollen, and pet dander.
FPR Rating 7 - filters out everything in FPR 4, plus small particles like bacteria and mold spores.
FPR Rating 9 - filters out everything in FPR 7, plus smoke, smog, microscopic allergens, and particles that can carry viruses.
FPR Rating 10 - filters out everything in FPR 9, plus particles that can carry odors.
MPR - Micro-particle performance rating
The MPR rating system, developed by 3M, again gives us the filter's efficiency rating. 3M claims that this method is scientifically better; however, we'll leave that to you to decide.
The MPR is calculated by measuring the effectiveness of a filter in capturing small particles ranging from .03 to 1.0 microns. This method assumes that if a filter can capture the small particles, it can also catch the large ones; this is partly true, as you can see in this video for a detailed explanation.
Generally, .03 microns is considered the most penetrating particle size (MPPS), which is why they use that as a benchmark.
You can read more here if you want to get scientific about it. Nonetheless, 3M doesn't explain how MPR is calculated in-depth.
MPR ratings range from 300 - 2800, with 300 being the lowest efficiency filter and 2800 being the highest efficiency filter.
You can see how 3M compares its filters to MERV ratings. However, the comparison is a bit lob-sided because it equates the highest efficiency MPR-rated filter to MERVs' third most efficient filter.
HEPA - High-efficiency particulate air filter
HEPA high-efficiency air filters are the highest-efficiency air filters you can get. HEPA filters filter out at least 99.7% of dust, pollen, mold, bacteria, and any airborne particles with a size of 0.3 microns. HEPA filters are more expensive and are typically found in hospitals, delicate manufacturing plants, and airplanes.
Many health-conscious individuals opt for a HEPA filter in their homes, and you can purchase a portable room HEPA filtration system online. However, we believe a whole-home solution is more thorough. You can contact an HVAC pro if you are interested in a whole-home HEPA filtration solution.
How to change an HVAC filter
How to change an HVAC filter located near the blower wheel
The main steps to changing a filter located near the blower wheel are:
Located the filter
Cut the power to the system
Open the filter housing
Remove the old filter
Replace with the new clean filter
Restore the power
Below we go in-depth and walk you step by step through how to replace the filter located at the blower wheel.
Once you have determined that the air filter is located near the blower wheel (fan) at the gas furnace or air handling unit, follow these steps to replace the air filter.
First, turn off the HVAC system. The best way to do this is by unplugging the air handling unit from the power. This ensures the fan won't kick on by accident. Replacing the filter when the system is on is dangerous and can cause damage to the system. The blower wheel (fan) and motor are powerful when on and can cause the system to get dirty as it sucks in dust and debris and can even cause physical injury if touched when it is working.
Next, open the filter housing or cabinet. Filters near the blower wheel (fan) can be either one or five-inch. The one-inch housing typically has one or two little screws that can be opened by hand. And the five-inch filters are typically in a cabinet that is popped into place and can be opened by hand.
Removing the old filter from the cabinet or housing should be easy. The filter slides out. Sometimes a little extra force is needed if the filter is sitting snug in place. Before removing the filter, notice if you see an arrow printed on the filter. This arrow indicates the direction of airflow.
Now is a good time to document the size of the old filter if a new filter needs to be purchased.
Before putting in the new filter, it is a good idea to write the filter change date with a sharpie or document it on the phone. You can also set a reminder to check the filter's cleanliness and decide when it needs to be replaced. Noting the filter change date is also crucial if there are any future problems with the HVAC system; a technician will need to know when the filter has been changed.
After documenting the replacement date, it is simple to slide the filter into the cabinet and securely close it. Just be sure that the arrow is pointing in the correct direction. The arrow lets us know what direction air is supposed to flow through the filter. Remember that air flows towards the blower wheel (fan) and motor when inserting the filter. So the arrow should be pointing toward the blower wheel (fan).
Now turn the HVAC system back on. You'll be surprised how many people forget this step and don't know why the HVAC system isn't working.
How to change an HVAC filter located at the grille (vent)
The main steps to changing a filter located at the return grille (vent):
Located the filter
Cut the power to the system
Open the filter housing
Remove the old filter
Replace with the new clean filter
Restore the power
Below we go in-depth and walk you step by step through how to replace the filter located at the return grille.
Once you have determined that the air filter is located at the return grille, follow these steps to replace the air filter.
First, cut the power to the HVAC system. Turning off the system can be done by disconnecting the air handling unit from the power, shutting down the electrical breaker, or turning off the power from the thermostat. If turning off power to the thermostat, ensure that all modes are off, including heating, cooling, and fan. Replacing a filter when the system is on can cause dust, dirt, or debris to enter the system and cause physical injury.
Once the power is off, open the grille housing. Usually, two to four levers allow you to open the grille and access the filter. The filter should be easily removable.
Now is a good time to note the filter size if a new filter needs to be purchased.
Before replacing the filter, it is a good idea to note the filter replacement date either on the side of the filter or on the phone. You can also set a reminder to check the filter's cleanliness and decide when it needs to be replaced. Documenting the filter change date is also crucial if there are any future problems with the HVAC system; a technician will need to know when the filter has been changed.
After noting the replacement date, it is simple to insert the filter into the grille housing and securely fasten it in place. Just be sure that the arrow is pointing in the correct direction. The arrow lets us know what direction air is supposed to flow through the filter. Remember that air flows towards the HVAC system. So the arrow should be pointing inwards toward the wall or ceiling.
Now turn the HVAC system back on.
Who would have thought that something as simple as a filter dramatically impacts the performance of your HVAC system and indoor air quality?
We covered a lot of topics, such as the importance of a clean air filter and how it improves air quality, saves you money, and is more sustainable. We discussed how often to replace an HVAC air filter and how to tell if yours is dirty. We discussed what filter you should buy, including sizes and choosing a filter efficiency rating, and we walked you through how to replace an air filter.
By now, you should feel confident that you know when and how to replace your air filter and what filter to buy when the time comes.
Changing your air filter is a simple task to incorporate into your home maintenance routine. It's one of the simplest ways to preserve your health and HVAC system and reduce energy costs simultaneously.
Consider buying a smart thermostat if you want a more accurate filter change reminder. A smart thermostat can monitor how long your fan runs to notify you when it is time to replace your filter. And if you want more comprehensive maintenance for your HVAC system, consider HVAC system cleaning or yearly HVAC system maintenance.
You can contact us or comment below if you have any questions.