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How Often To Change Your HVAC Filter

Learn how often to change your HVAC filter, as well as general knowledge about HVAC filters and how to replace them.

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An HVAC system, in most cases, is a long-term and expensive investment. But most of us don’t know how often to change your HVAC filter. No homeowner would like to see their heater quit on the coldest night of the winter or the warmest night of the summer..

With that being said, taking care of your HVAC system is important if you’d like to ensure longevity, and one of the most important things you can do to take good care of your HVAC system is to simply change its filter on a regular basis.

In fact, you’d be surprised at how you can keep your HVAC energy bills low just by changing the filter. Yet, many homeowners often forget to do this simple task for one reason or another. 

If it’s only for a slightly higher electricity bill due to a clogged filter, probably it’s not going to be a major issue (although it will accumulate.) Unfortunately, failure to replace a clogged or broken air filter may cause future maintenance issues and even permanent damage to the HVAC system.

So, how often should you change the HVAC filter?

In this article, we will share some general recommendations and best practices to help you figure out the best possible time and schedule for your HVAC system.

Let us, however, start from the basics: how do HVAC filters work?

How do HVAC Filters Work?

Most people understand that HVAC filters play an important role in cleaning the air before it enters the HVAC system and when releasing the air back into the room or building.

As you might have guessed, the primary role of the HVAC filter is to trap dirt, pollen, dust, and other particles from entering or exiting the HVAC system, ensuring only clean air is circulated to your room.

On the other hand, dust and debris may damage the HVAC equipment when it enters the system, and the filter will also prevent this from happening.

So, we can say that HVAC filters offer two levels of protection:

  1. Protecting the internal components of the HVAC system: the filter or filters prevent airborne particles from entering the HVAC system. Dust, dirt, and pollen may lower the performance of the HVAC system and, when accumulated, may damage the internal components of the HVAC system.
  2. Ensuring clean indoor air quality: the air filters keep particles, allergens, and pollutants from being distributed into the room by the HVAC system, so you can ensure clean air quality inside the room.

While HVAC systems can technically work without filters, running your system without filters may cause it not to run optimally, leading to condensation issues, deteriorated air quality, and other issues, and it may reduce the longevity of your system due to the damaged components.

Why Do You Need to Replace Your HVAC Filters?

Since the filters are consistently in contact with dust, debris, and other particles, naturally, they will get clogged after some time, which can cause these disadvantages:

  • Clogged filters will reduce airflow inside the system, which can wear the blower fans faster than it should.
  • It will also obstruct the airflow coming out of the HVAC system, so the system will be less effective in cooling or warming the room, and the air inside the building will also contain more pollutants.
  • Obstructed airflow would translate into increased energy usage, which will, in turn, increase your energy bills. 
  • Clogged filters can cause damage to the internal components of the HVAC system and, in a worst-case scenario, may cause irreparable damage to the entire system.

How Often Should You Change Filters in Your HVAC System?

How Often To Change Your HVAC Filter

There’s no one-size-fits-all answer for this. There are different types of air filters available with different specifications (more on this later), and how often you should change your HVAC air filter would depend on how long your specific type of filter is expected to last, as well as different factors in your building that may affect the service life of the HVAC filter.

In general, however, changing your air filters once every three months is considered pretty safe. 

Here are some additional considerations:

  • Very affordable fiberglass filters aren’t very durable and will get clogged often. You may need to change them once every 30 days or so.
  • On the other side of the spectrum, more expensive pleated filters can last longer, and you might be able to get away with changing them up to every six months, if not more.
  • The size and the thickness of the filter would also play into factor:
    • Smaller air filters between 1 and 2 inches in thickness should be replaced about every one to three months.
    • Medium-sized air filters between 3 and 4 inches in thickness can be replaced once every six to nine months.
    • Larger-sized filters of 5 inches in thickness or larger can be changed after nine months or once every year.
  • The smaller the MERV ratings (more on this below) of the filter, typically, the more frequently they’ll need to be replaced.
  • Typically the larger the size of your home/building, the more frequently you’ll need to replace your filters and vice versa. An HVAC system in a large house is required to pump more air to reach the same amount of temperature compared to smaller homes, so naturally, the filters will ‘work’ harder.

Although more expensive and larger/thicker filters can theoretically go longer before they need to be replaced, an old filter would collect more dust, debris, and pollutants than a brand-new one, which will lower the efficiency of the HVAC system. So, even with more expensive and theoretically more durable filters, we’d recommend not letting the filters go unreplaced for more than three months. 

However, there are also some reasons to consider that may require you to change the filters more often:

  • Frequency of use: pretty self-explanatory; the more you use the HVAC system, the faster your filters will clog up, and the more frequently you’ll need to replace them.
  • Air quality: the replacement cycle of your HVAC filters would also be affected by outdoor and indoor air quality in your area. If the surrounding air is polluted or dirty, then you’ll need to replace the filters much more frequently. Having poorer air circulating in your HVAC system may cause malfunctions and often permanent damages. 
  • Allergies: if someone in your house or building has allergies, including asthma, you should replace the air filters more frequently, not longer than every 45 days. People with allergies are more sensitive to dust and other allergens, so any longer periods than this can be dangerous for them.
  • Having pets: animals can shed their furs and quickly clog up your air filters, so you’ll need to change these filters more frequently, not longer than every 60 days.

MERV Ratings for HVAC Filters

MERV, or Minimum Efficiency Reporting Value, is a standard rating used to measure the performance and efficiency of filters. MERV ratings for HVAC filters are indicated as numbers, typically between 1-16. However, there are some very efficient filters with a rating above 16, although they are very rare and expensive.

The higher the MERV rating, the more efficient the filter is, but typically systems that use high-MERV filters are also more expensive.

For HVAC systems that are going to be installed in a typical residential home, HVAC filters with a rating of 7-10 would be sufficient:

  • MERV 1-4: can filter particles larger than 10.0 microns, including typical dust particles, pollen, and carpet fibers., the least effective and also the least expensive filters. Provide only minimal protection against dust, and they need to be replaced more often since they are flat instead of pleated.
  • MERV 5-8: can filter particles larger than 3 microns in size, which include mold spores and cement dust. These are the medium-quality filters sufficient for most HVAC systems in typical residential homes.
  • MERV 9-12: high-quality air filters, capable of filtering particles larger than 1 micron in size, including Legionella, coal dust, Nebulizer dust, and more. The U.S. Environmental Protection Agency considers HVAC filters with MERV ratings between 9-12 as high-quality filters that are almost as effective as true HEPA (High-Efficiency Particulate Absorption) filters, so they are very effective, although they may be too expensive for residential applications.
  • MERV 13-20: can theoretically filter particles larger than 0.3 microns; these filters are pretty rare in residential applications since most residential HVAC systems won’t accommodate these filters without sufficient modifications.

Again, the lower the MERV ratings of your filters, the more affordable the filters will be with lower efficiency, and yet you’ll need to replace them more frequently. Take this into consideration if you are on a tight budget.

When you are replacing your filters, make sure to check the old filter’s MERV rating so you can get the right replacement. 

How Often To Change Your HVAC Filter: Choosing The Right Filter Size

How Often To Change Your HVAC Filter

When it comes to changing your HVAC filter, choosing the right size also matters. 

HVAC filters are typically labeled with three-part dimensions (length x width x depth). For example, 18″ x 30″ x 1″ means that the filter is 18 inches long, 30 inches wide, and 1 inch thick/deep.

Are You Using The Right Filter Size for Your HVAC System?

Using the wrong filter size won’t only make the HVAC system less efficient than it should be but may potentially recirculate dust, dirt, and other pollutants back into the building’s circulating air due to the gaps created and may cause damage to the HVAC system’s internal components due to accumulation of particles.

Here are some signs that you are using the wrong size HVAC filter:

  • If you notice an increase in dust or pollutants around our home or building, it may be a sign that your filter is too small.
  • If there are rattling noises in your HVAC system, it’s a common sign that your filter might be too small. 
  • If it’s too difficult to fit the filter into the slot, it might be too big, especially if you really need to force it into the slot. 
  • If your filter is damaged (i.e., bent frames) when taken out, it’s too big for the slot.

If you are still unsure about whether you are using the right filter size, call an HVAC professional to confirm and help with the replacement.

How to Measure your Filter

Some filters are labeled, so you can see the nominal/advertised size printed on the size of the filter. 

Simply turn the HVAC system and/or thermostat off, then remove the air filter, and check whether it’s labeled. If yes, then you shouldn’t worry about getting the right replacement filter size.

If your current air filter is not labeled, then, unfortunately, you’ll need to do manual measurements.

Manual Measurement of HVAC Filters

You can measure the old HVAC filter with a tape measurer or a long enough ruler. Measure the filter’s length, width, and thickness in inches.

However, typically a filter’s advertised size is slightly bigger than the actual measurements, typically 1/4 to 1/2 inch less than its advertised size. If you are measuring your filter with a measuring tape, round each dimension up to the nearest inch to get the advertised/nominal size. 

Once you’ve rounded up the measurement and got the nominal size, you can shop for a new replacement filter with this nominal size.

If Your Existing Filter is The Wrong Fit

If there are signs that your current filter is the wrong size and you’d like to know the correct filter size, unfortunately, the only way is to measure the filter’s intake slot.

First, you’ll need to locate this intake slot, which is usually located in the blower compartment or return duct. Find the slot’s innermost edge, and measure the length, width, and thickness. 

Once you’ve got the measurements of the slot, the replacement filter should be ⅛ to ⅝ inches less than the slot. Do not get a filter with the exact same size since it won’t fit properly in the slot.

If There’s No Slot

Albeit rare, there are HVAC systems with filters that sit in a vent rather than sliding into a slot. In this case, get the measurements of the vent, and get a replacement filter that is around 1/8 inch shorter than the vent’s height and width.

Keep in mind that if you are doing manual measurements of your slots or vents, make sure to use the actual sizing rather than the nominal/advertised sizing. Every brand makes filters with slightly different actual sizes, so make sure to measure the filter’s exact measurement at the shop before buying. 


The information we’ve shared above should provide you with enough knowledge on how often you should change the filters in your HVAC systems, as well as general knowledge about HVAC filters and how to change them.

If you are still not sure about how or when to replace the filters in your HVAC equipment, Cocoon Home Services provides you with an easy way to get help for installing or servicing your HVAC system with just a single tap, click, or phone call. 

Sign up with Cocoon today, and we’ll send a Cocoon ServicePro to help with your HVAC system and maintenance right away.