The right HVAC filter has to do two things well: capture the particles you want to remove and still allow the heating and cooling system to move the air it needs.
That sounds simple, but homeowners are faced with a surprising number of choices. Filters come in different sizes, thicknesses, materials, and efficiency ratings, and the package often suggests that a higher number must always be better.
It is not quite that simple.
For many Central Oregon homes, a good filter choice depends on the HVAC system, the filter cabinet, the level of filtration you want, and conditions inside the home. Pets, household dust, wildfire smoke, remodeling, and how much the HVAC equipment runs can all affect how quickly a filter becomes dirty.
There is also no universal schedule that says every HVAC filter should be changed every 30, 60, or 90 days. The better approach is to use the right filter for the system and check it often enough to learn how quickly it loads in your particular home.
What Does an HVAC Filter Do?
A forced-air HVAC system continually moves household air through the furnace or air handler and back through the duct system.
The filter sits in that airflow path and captures particles before they continue through the equipment and back into the house.
One of its most important jobs is protecting the HVAC equipment from accumulating dust and debris. A good filter can also reduce airborne particles circulating through the home, with higher-efficiency filters capturing smaller particles than basic filters.
EPA describes central HVAC filtration as one useful part of improving indoor air quality, while also noting that filtration cannot remove every type of indoor pollutant.
That distinction is helpful. An HVAC filter can be very useful without being a complete indoor-air-quality solution by itself.
What Does a MERV Rating Mean?
MERV stands for Minimum Efficiency Reporting Value. It is a standardized rating used to compare how effectively filters capture particles between approximately 0.3 and 10 microns.
In general, a higher MERV rating means better capture of smaller particles.
Common residential filter choices include:
- MERV 8: useful basic filtration for household dust and equipment protection
- MERV 11: improved particle filtration while remaining appropriate for many residential systems
- MERV 13: substantially better capture of smaller particles, including the fine particulate matter that becomes particularly important during wildfire smoke
EPA recommends MERV 13, or the highest-efficiency filter the HVAC system can accommodate, when improved fine-particle filtration is the goal.
That does not mean every Central Oregon homeowner should automatically install a MERV 13 filter in every furnace.
The system still needs to move air through it.
Is a Higher MERV Rating Always Better?
Not necessarily.
Better filtration is useful, but every filter creates some resistance to airflow. The HVAC blower has to pull or push air through the filter as it circulates air through the house.
If a filter is too restrictive for the system, airflow can be reduced. That can affect comfort and equipment operation.
The goal is therefore not to install the highest MERV number available. It is to use the highest useful filtration level that the system and filter arrangement can handle properly.
EPA gives similar guidance, recommending MERV 13 or as high a rating as the system fan and filter slot can accommodate.
In many systems, MERV 13 works very well. Other systems may need a different approach, particularly if they have a small filter area, restrictive ductwork, or an older blower.
What Is the Difference Between a One-Inch Filter and a Media Filter?
Two filters with the same MERV rating can behave differently.
A common one-inch filter has relatively little surface area. A deeper media filter—often four or five inches thick—can contain substantially more pleated filter material within the same general opening.
That additional surface area allows air to pass through more filter media and gives the filter more capacity to hold dust before it becomes loaded.
This is one reason a deeper media filter can sometimes provide higher-efficiency filtration with less resistance than a very restrictive one-inch filter.
Coleman, for example, offers whole-home media air cleaners using MERV 11 and MERV 13 filters designed to integrate with a central HVAC system.
For homeowners who want better filtration, changing the filter cabinet can sometimes be a better solution than repeatedly trying to fit a more restrictive filter into a small existing slot.
Which MERV Rating Makes Sense for Your Home?
There is no single answer for every home, but a reasonable starting point is to use a good pleated filter that provides useful filtration without unnecessarily restricting airflow.
For many residential systems, that may mean a MERV 8 or MERV 11 filter. MERV 13 may be appropriate when improved fine-particle filtration is important and the HVAC system can accommodate it.
The decision can change depending on the household.
A home with pets may collect substantially more hair and dander.
A home near active construction or a dusty unpaved area may load filters faster.
A household concerned about wildfire smoke may place a higher priority on fine-particle filtration.
A system with a large media cabinet may have more filtration options than a furnace using a small one-inch filter slot.
Rather than treating one filter rating as universally correct, we prefer to match the filter to the HVAC system and what the homeowner wants it to do.
How Often Should You Change an HVAC Filter?
The most accurate answer is: when it needs to be changed.
The familiar 30-, 60-, and 90-day recommendations can be useful reminders, but they are not laws of HVAC.
EPA notes that manufacturers commonly recommend replacement around every 60 to 90 days, while also emphasizing that filters should be changed more frequently when they become heavily soiled. ENERGY STAR recommends checking filters monthly, particularly during periods of heavy heating or cooling use.
For a homeowner learning a new system, checking the filter once a month is a good way to establish what is normal.
If it still looks relatively clean after a month, check it again later. If it is heavily loaded in three or four weeks, something about the home or system is causing it to collect particles quickly.
Over time, you can usually develop a realistic replacement schedule for your own house.
What Makes a Filter Get Dirty Faster?
Filter life depends on how much particulate matter passes through the HVAC system.
Several common conditions can shorten the interval between changes:
- Pets
- Wildfire smoke
- Construction or remodeling
- Unusually dusty conditions
- Open windows during dusty weather
- A large household
- Frequent HVAC fan operation
- Heavy heating or cooling use
- Carpeting and other indoor dust sources
Central Oregon can produce some particularly demanding conditions. A filter may remain relatively clean during one part of the year and load quickly during a period of wildfire smoke, heavy summer dust, or nearby construction.
That is why a calendar alone cannot tell you what condition the filter is in.
How Does a Dirty Filter Affect the HVAC System?
As a filter captures particles, it gradually becomes more restrictive.
If it becomes heavily loaded, the blower has to work against greater resistance and system airflow can decrease.
ENERGY STAR notes that dirty filters can slow airflow, increase energy use, and contribute to equipment problems.
That is one reason changing filters is one of the simplest maintenance tasks a homeowner can perform.
The goal is not to discard a perfectly usable filter simply because a date arrived on the calendar. It is also not to leave one in place until it is packed with debris.
How Can You Tell When a Filter Needs Changing?
The easiest method is to look at it.
Some discoloration is normal. A filter is supposed to collect particles.
What you are watching for is substantial loading across the filter media. If the filter is visibly covered with dust and debris or has become significantly darker throughout the pleats, it is probably time to replace it.
It can be useful to compare a used filter with a new one of the same type until you become familiar with how yours looks over time.
If filters are consistently becoming heavily loaded much faster than expected, that can also be worth investigating rather than simply accepting unusually frequent replacement as normal.
What Size HVAC Filter Should You Buy?
Filter dimensions matter.
A filter should fit its rack or cabinet properly without being crushed, bowed, or leaving large gaps around the edges.
EPA recommends a snug fit because air that bypasses the filter around the edges is not being filtered.
The size is usually printed on the edge of the existing filter. Keep in mind that the labeled or nominal size may differ slightly from the filter's exact physical dimensions.
If you are unsure what size belongs in the system, use the dimensions specified for the filter rack or media cabinet rather than guessing from the available space.
Which Direction Should the Filter Arrow Point?
Most disposable HVAC filters have an airflow arrow printed on the frame.
That arrow should point in the direction the air is traveling toward the furnace or air handler blower.
Depending on the installation, the filter may be located beside the furnace, below it, in a return-air cabinet, or behind a return grille somewhere in the house.
If you are unsure which way air moves through the system, note the direction of the existing filter before removing it or ask us to show you during a service visit.
It is a small detail, but installing the filter in its intended orientation helps it stay properly supported by the air pressure passing through it.
Should You Install Filters in More Than One Location?
Usually not unless the system was intentionally designed that way.
Some homes have filters at the central equipment. Others use filter grilles at one or more return-air locations.
Adding an extra filter simply because there is space for one can create unnecessary airflow resistance.
If your system appears to have more than one filter location, it is worth confirming how it was designed before putting filters everywhere you find an opening.
More filters do not automatically mean better filtration.
Is a More Expensive Filter Better?
Sometimes.
Price alone does not tell you whether a filter is appropriate for the HVAC system.
A more expensive filter may provide better particle capture, more filter surface area, stronger construction, or a longer service interval. Those can all be valuable.
Other premium features may not matter for what you are trying to accomplish.
The useful questions are:
Does it fit correctly? Is the filtration level appropriate? Can the system move enough air through it? Does it provide a meaningful benefit for this household?
If the answer is yes, paying more for the right filter can make sense.
If the filter is unnecessarily restrictive or solves a problem you do not have, a higher price does not make it better.
Can an HVAC Filter Improve Indoor Air Quality?
Better filtration can reduce the amount of airborne particulate matter circulating through a forced-air system.
That can include dust, pollen, pet dander, and other particles, depending on their size and the efficiency of the filter.
We would be careful about promising that a particular HVAC filter will solve allergies or other health conditions. Indoor air quality is influenced by many things, and an HVAC filter only treats air when that air passes through the system.
For households wanting better particle filtration, however, moving from a basic filter to an appropriately selected higher-efficiency filter or larger media cabinet can be a meaningful improvement.
EPA identifies HVAC filtration as a useful supplement to source control and clean-air ventilation when improving indoor air quality.
What About Filters During Wildfire Smoke?
Wildfire smoke deserves special consideration because the particles of greatest concern are much smaller than ordinary visible household dust.
EPA recommends MERV 13 filtration, or the highest-efficiency filter the system can accommodate, when wildfire-smoke particles are a concern.
Filters may also load more quickly during sustained smoke events and should be checked more frequently.
We cover this in much more detail in our Wildfire Smoke, HVAC Filters, and Indoor Air in Central Oregon guide, including fan operation, portable air cleaners, smoke infiltration, and MERV 13 filtration.
For this page, the important point is that smoke season can change both the type of filtration you want and how often the filter needs attention.
How Are Ductless Filters Different?
Ductless systems handle filtration differently from a central furnace or air handler.
Most ductless indoor units contain washable filters primarily intended to protect the indoor coil and capture larger particles. They generally do not provide the same fine-particle filtration as a high-efficiency central media filter.
EPA notes that wall-mounted ductless equipment is generally designed primarily for temperature control, with more limited filtration than high-efficiency central filters or portable air cleaners.
Those filters need to be removed and cleaned regularly according to the equipment manufacturer's instructions.
If a ductless home needs additional fine-particle filtration, a properly sized portable HEPA air cleaner can often complement the heating and cooling system.
Can You Upgrade to a Larger Filter Cabinet?
Often, yes.
If an existing furnace or air handler uses a small filter arrangement, it may be possible to install a larger media-filter cabinet.
That can create more surface area and allow better filtration while maintaining appropriate airflow.
Coleman offers MERV 11 and MERV 13 whole-home media air cleaners specifically designed to integrate with a central HVAC system.
Whether that kind of upgrade makes sense depends on the available space, return ductwork, airflow, and what the homeowner wants to accomplish.
A whole new furnace is not necessarily required just because you want a better filter.
Does a Dirty Filter Mean Something Is Wrong?
A dirty filter is doing its job, so frequent loading does not automatically mean there is a problem.
But if a filter becomes heavily loaded far faster than expected, it can be useful to think about why.
Has there been construction in or around the house? Are wildfire conditions unusually bad? Are there several pets? Is the blower running continuously? Is there excessive dust entering through return ductwork or another part of the home?
If the behavior suddenly changes, that information can be helpful.
The solution may simply be more frequent filter changes during that period. In other situations, there may be something about the home or HVAC system worth looking at.
How Deschutes Approaches HVAC Filters
We do not think homeowners need the most expensive or highest-rated filter available simply because it exists.
We want the filtration to make sense for the HVAC system and for the people living in the home.
If a basic pleated filter is providing the filtration you want and the system is operating properly, there may be no reason to complicate it.
If wildfire smoke, pets, household dust, or another concern makes better particle filtration valuable, we can look at whether the existing system can accommodate a higher-efficiency filter or whether a larger media cabinet would be a better approach.
The priority is to improve filtration without sacrificing the airflow the HVAC equipment needs.
We can also show you where your filter is located, which size to buy, how it should be installed, and what a reasonable inspection schedule looks like for your home.
The Bottom Line
There is no single HVAC filter or replacement schedule that is right for every Central Oregon home.
The best filter is one that fits properly, provides the level of particle filtration you want, and allows the HVAC system to maintain appropriate airflow. MERV 8 and MERV 11 filters can be good choices for many residential systems, while MERV 13 is often useful when finer-particle filtration is a priority and the system can accommodate it.
Rather than relying only on a 30-, 60-, or 90-day rule, check the filter regularly and learn how quickly it becomes dirty in your home. Pets, wildfire smoke, dust, remodeling, season, and HVAC runtime can all change that interval.
If you are unsure what filter your system should use—or whether your current system can support better filtration—contact us. We can look at the equipment and filter arrangement and help you choose an option that improves filtration without creating an airflow problem.