Air filters are an important component of HVAC systems that trap dust, pollen, pet dander, and other airborne particles, preventing them from propagating through your home. As particles build up on the air filter over time, the filter medium will become clogged and dirty, making it harder for air to pass through.
Eventually, the filter will no longer be effective, and you should replace it with a new one. But how often do air filters need to be replaced?
The general advice for standard 1” thick pleated furnace filters is to replace them every 90 days, but that applies to filters of a particular type in an average domestic environment. It also assumes air cleanliness requirements that may not be sufficient for some families.
In fact, the ideal air filter replacement schedule depends on several factors, including the type, quality, filtration efficiency, environmental conditions, the healthcare needs of residents, and more.
The best way to know whether an air filter should be replaced is to inspect it. In this article, we’ll explore the factors that impact air filter maintenance schedules, and provide an air filter inspection and replacement guide to help you get the best efficiency, performance, and filtration from your HVAC system.
Why Change Your Air Filter?
Changing air filters has several significant benefits for your home’s HVAC system and indoor air quality.
Restores Air Flow and Ventilation Efficiency
A clean filter with low airflow resistance allows your HVAC system’s fans and air handlers to move air through ductwork unimpeded, reducing the strain on components like blower motors and compressors. It allows them to operate as designed for optimal efficiency, performance, and longevity.
With lower resistance, your HVAC system doesn’t have to work as hard to move the same volume of air. Less work means lower electricity bills.
Traps Particles and Prevents Recirculation
Dirty filters become full of trapped contaminants over time, including dust, dander, mold spores, bacteria, cleaning chemicals, vehicle exhaust, pollen, and more. With a clogged air filter, particles can dislodge, re-enter the air stream, and blow back into your home’s living spaces.
Particle recirculation makes it challenging to improve indoor air quality. By catching these particles in a new, clean filter, you can safely dispose of them rather than allowing them to spread throughout your home.
Protects HVAC Components from Premature Wear and Tear
All central HVAC components—from fans and motors to heat exchangers and air handlers—endure extra stress when they operate with a restricted airflow. They strain more to move air against excessive filter resistance.
Increased wear and tear can lead to breakdowns and equipment failure. Replacing clogged filters reduces strain on components and helps fans, motors, and related equipment achieve normal lifespans.
How Often Should You Change HVAC Air Filters?
HVAC professionals recommend replacing typical 1 inch pleated air filters about once every three months or 90 days. But, as we said, general guidelines assume the typical use of an average efficiency filter (MERV 8 to MERV 13 one inch thick pleated air filter) under normal operating conditions.
Many variables can affect ideal replacement intervals, including:
- Filter Type: Under normal operating conditions, non-pleated panel woven nylon filters are typically replaced every 30 days. One inch thick pleated filters are generally replaced every 90 days. Whole house filters which are anywhere from 3 to 6 inches are typically replaced on intervals from 6 to 12 months depending on the manufacturer specifications.
- Filter efficiency: High-efficiency filters trap more particles and may have increased air resistance and may need changing more frequently.
- Outdoor air quality: Homes in areas with higher outdoor pollution may need to change filters more often.
- Number of pets: Pet dander and hair often lead to more rapid filter loading.
- Level of use: The more you use your HVAC system, the faster filters become clogged. They may need more frequent replacement during periods of peak use, like the height of summer and winter.
- Home size: In larger homes, more air will be passed through air filters to achieve adequate heating or cooling. More airflow means faster degradation of air filter efficiency.
While 90 days is a reasonable starting point, observing your filter’s condition is better than relying on a calendar schedule alone.
Health and Environmental Considerations
Certain health conditions and environmental factors may mean you need to change filters more often than 90 days. They include the following.
- Allergies: Individuals sensitive to pollen, mold, pet dander, and other allergens trapped by the filter are advised to change filters monthly during peak seasons of irritation.
- Asthma and respiratory illness: Reducing airborne particles with high-efficiency air filters can help minimize asthma attacks and complications. These filters require replacement more often than less effective filters.
- Wildfires and severe pollution: Heavy smoke, soot, and ash loading from nearby wildfires, as well as high outdoor pollution levels, can rapidly block filters.
- High dust conditions: Home remodeling and woodworking projects add fine particulate matter to indoor air. Upgrade filters and change monthly when operating under very dusty conditions.
Air Filters by Capability
Air filters are rated by MERV (Minimum Efficiency Reporting Value). MERV represents a filter’s ability to capture particles of various sizes. As MERV ratings increase, filters trap more particles and may restrict airflow faster as they become saturated.
- MERV 1–4 filters stop only large particles like hair and lint. They should be changed more frequently at least every 30 days.
- MERV 5–7 filters trap most pollen and mold spores. If they are pleated 1 inch filters, they should be changed at least every 3 months. If they are a flat panel filter, they may require more frequent changing.
- MERV 8–12 air filters smaller particles like some bacteria and smoke. Change every 1–3 months for 1 inch pleated filters and change every 6-12 months for 4 inch pleated filters.
- MERV 13+ filters remove up to 99% of particles and may need changing every 2–3 months for 1 inch pleated filters and change every 6-12 months for 4 inch pleated filters.
Remember, these are rough guidelines. As we’ve explained, many factors impact ideal replacement schedules, and it’s better to regularly inspect air filters than rely on guidelines that don’t fit your unique circumstances.
Air Filters by Type
Several common types of HVAC filters are available, each with different typical capacities and recommended change intervals.
Fiberglass Air Filters
Standard fiberglass filters are cheap, disposable panels made of woven glass fibers, typically rated MERV 1–4. They provide minimal filtration, only trapping some large particles like hair and lint. When clean, fiberglass filters have very low airflow resistance. These filters are generally replaced every 30 days and the primary purpose is to protect the HVAC equipment.
Inexpensive fiberglass filters can typically operate for 30 days and more between changes. However, they are not recommended for those with allergies or respiratory issues because of their low efficiency.
Pleated Filters
Standard 1” inch thick Pleated air filters are made of synthetic blend media arranged in tight pleats. The added surface area allows for longer life before a replacement is needed. Under normal operating conditions, pleated filters have a typical life span of up to 90 days between filter changes. Deeper pleated air filters such as 2 inch, and 4 inch thick air filters can have a longer life. For instance, a 4 inch pleated air filter can have a life span of 6 months or longer.
Electrostatic Filters
Triboelectric filters are considered one of the best materials for filter media since they are manufactured using materials with dissimilar charges and retain their electrostatic properties for the life of the filter. These types of filters are typically replaced every 90 days for 1” thick standard pleated filters. For 4” pleated filters, they are typically replaced every 180 days.
Some electrostatic filters are made of fabric or foam layers with an electrostatic charge applied during manufacturing. The charge attracts and captures smaller airborne particles like smoke.
When new, charged electrostatic filters can filter tiny particles but lose efficiency over time as pores become infiltrated and clogged. Airflow resistance can increases more quickly in electrostatic filters, so you should inspect to see if they need replacing at least every 60 days.
High-Efficiency Air Filters
High-efficiency filters use denser filtration material to capture very small particles. This category includes HEPA and MERV 13+ rated filters, which can remove up to 99% of particles, bacteria, viruses, and allergens.
High-efficiency HVAC filters are only suitable for HVAC systems that can cope with the increased static pressure, as we explained in Merv 11 vs Merv 13 Air Filters. Plus, they may develop high airflow resistance more rapidly as pores become infiltrated and clogged with particulates. Modern HVAC equipment can support the higher air flow but older systems may require a lower MERV filter.
As a result, high-efficiency filters may need replacement as often as every 30–90 days for standard 1” deep pleated filters and replaced every 6 Months for 4 inch deep pleated filters.
Learn more about air filter types and sizes in our Air Filter Knowledge Base.
How to Inspect Your Air Filter
You don’t need advanced equipment to determine when to change your air filter. Simply remove your existing filter and visually inspect its condition. Some high end systems may have air sensors, but most systems do not. When a red light or notification comes up on your thermostat to change a filter it was probably set on a 30 or 90 day interval by the HVAC tech that installed the system. It can usually be reset by pushing a button on the thermostat. Consult your thermostat manual for the exact process for your model.
- Check if dust and dirt are collecting around air vents.
- Check for layers of visible dust and debris on the filter restricting airflow.
- If the filter has become misshapen over time, air and particles can bypass the filter, impacting effectiveness.
You may also notice other signs that air filters are not performing as they should. If your heating and cooling system takes longer to achieve your desired temperature than usual, clogged filters are one possible culprit. If your energy bills increase unexpectedly, it may be because your HVAC system is consuming more energy to push air through dirty filters.
A routine monthly inspection will help you determine your filter’s condition and whether it needs replacing. Over time, you will develop an understanding of how often they need replacing and how changing seasons and conditions affect filter efficiency.
How to Change Your Air Filter
Replacing most HVAC air filters is a simple DIY task. Before replacing your filter, check its documentation to determine which size and type of filter is recommended. Buy a filter that your air conditioner manufacturer recommends. For more information, read our guide to choosing the right air filter.
At Atomic Filters, we stock a comprehensive range of high-quality AC air filters rated MERV 8, MERV 11, and MERV 13.
Once you have your new air filter, installing it is straightforward.
- Turn off your HVAC system at the breaker panel or switch to avoid the fan turning on.
- Locate the air filter access cover on the air handler, the return duct, or the grill.
- Slide out the existing air filter.
- Verify the new filter is the right size.
- Gently slide the clean air filters into the tracks with the arrows pointing in the direction of airflow.
- Replace the access door, close it firmly, and turn the HVAC back on.
- Properly dispose of old filters since they may contain trapped hazardous particles.
- Make sure to reset your thermostat “change air filter” notification.
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