Filters the most particles out of the air and is easily the most effective filter you can buy.
Expensive and may be overkill unless you have crippling allergies, pets, or other problems that lead to a dirty home.
Attracts and filters out all kinds of crud; a premium filter for a very good price.
If you have pets, smoke, run your fireplace or have a lot of dust, this filter probably won't last three months.
Draws in dirt like a magnet thanks to electrostatic filter; filters out very small dust particles; hypoallergenic.
Can be overwhelmed by too much crud in the air, meaning you might have to replace it more often than you'd like.
Highly effective. Can be washed instead of having to replace it with a new one.
It's a bit expensive, but you will save money in the long run because it is a permanent replacement.
We purchase every product we review with our own funds — we never accept anything from product manufacturers.
We purchase every product we review with our own funds — we never accept anything from product manufacturers.
Choosing a replacement furnace filter might not sound like a difficult task, but when you look at the numerous options available, your decision may suddenly become surprisingly complex and confusing.
The easiest choice is to get an exact replacement of what you already have. But is that costing you more than it should? Are you getting the most efficiency from your system?
So maybe you’ve decided to look for an alternative. But which one? That's where BestReviews comes in!
We have our own test facilities so we can evaluate an enormous range of products. We consult with experts – in this case, HVAC specialist Allen Rathey – to make sure we cover every aspect of furnace filters, from construction to performance.
We also review feedback from hundreds of ordinary users to get their opinions.
Most importantly, we do it all independently. We never accept free samples from manufacturers. When we recommend products – like the excellent filters above – it's as a result of completely honest and unbiased investigation.
If you're ready to buy a furnace filter, it's our opinion that you can't do better than those in our product matrix above.
If you'd like more detail, the following furnace filter report explains in detail what lead us to our decisions.
Allen Rathey is a cleaning expert who promotes healthier indoor spaces. He is past-president of the Housekeeping Channel and the Healthy House Institute, and principal of the Healthy Facilities Institute (HFI) culminating more than 30 years of experience in making indoor places cleaner. He has been tapped as an expert by the New York Times, Real Simple, U.S. News & World Report, and other national media.
A filter might seem like a fairly insignificant part of a furnace or A/C system, yet good airflow is vital. If your filter is clean, your system works efficiently. If it's clogged and dirty, your system works harder than it should. That means higher bills and lower air quality.
Some suggest that a little dust is no bad thing, that it can actually improve filtration. That's not really an accurate reflection of what's going on, as expert Allen Rathey points out.
“Less-efficient filters get more efficient as they load, since the pores begin to fill and spaces between the media fibers get smaller, and they start trapping finer dust." However, this “advantage” is short-lived. The filters continue to clog quickly, and the dust soon dramatically restricts airflow.
The best solution is a proper maintenance schedule. It's a good idea to keep a log, check your filter regularly, and replace it as recommended by the manufacturer (or if you notice its performance starting to deteriorate).
It's false economy to try to extend the life of filters beyond their specifications. Any money you might save on the filters themselves is lost on higher energy bills. If anyone in the household has respiratory difficulties, you're also making things tougher on them.
If you've been having work done in your house, it has likely created lots of extra dust. Check your furnace filters for blockages.
Filters usually have an aluminum, steel, or plastic framework containing a filtering element made of fiberglass, polyester, cotton, or paper. They're designed to trap particles of dust and dirt that adversely affect the components and performance of your system and have a negative impact on household air quality.
The majority of filters are pleated, offering a large surface area without increasing the exterior dimensions.
Filters can be disposable or washable. Disposable filters are convenient, easy to change, and usually last several months. Washable filters can last years if looked after properly. But they must be cleaned regularly (usually every 30 days) and thoroughly. If not done correctly, there is a danger of spreading bacteria.
Most furnace filters have a front and back. It's important you fit yours the right way, or airflow will be compromised. Instructions will be provided, so read carefully. Often, there's also an arrow on the side indicating the correct direction.
There are two things to check when choosing a replacement furnace filter: size and filtration level.
It's important to get the right size, as there's no room for maneuvering. Furnace filters either fit or they don't.
Sizing should be clear from your existing filter and will be given as the width x height x thickness –16x25x1, for example. These measurements are in inches, but the inch marking is not normally shown.
Most filters are one inch thick, but some are two or even four inches thick. In theory, a thicker filter gives greater filtration – but they aren't interchangeable. If your existing filter is one-inch thick, a four-inch filter isn't going to fit without serious modifications to your system. Even if that were practical (which is unlikely), your system likely only has sufficient airflow for a one-inch filter anyway. Putting a thicker version in would actually reduce effectiveness.
MERV is the universal rating for filter quality, but there are two others. MPR (Microparticle Performance Rating) was introduced by 3M. Figures for MPR can be as high as 1,900, but the measuring method is completely different, so it's impossible to compare it with MERV. FPR (Filter Performance Rating) is Home Depot's rating. It goes from one to 10, with 10 being the best. Again, there's no direct comparison with the MERV rating.
The vast majority of disposable furnace filters are rated according to the MERV scale (Minimum Efficiency Reporting Value) created by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. The higher the number, the finer the filter, so the more particles it traps.
Disposable filters offered for household use vary between MERV 6 and MERV 12. However, experts recommend MERV 8 as a minimum and MERV 10 or 11 for better odor control.
Commercial filters are available with much higher MERV ratings, but most household systems don't generate sufficient airflow, so they should not be used.
Washable filters are not covered by MERV ratings, and their specifications can seem confusing. Some claim to trap a certain percentage of airborne particles, but they don't tell you what size those particles are. Our expert explains:
“Manufacturer claims such as “removes 95% of dust” are meaningless without knowing the size/type of particles you are discussing. A very poor (airy) filter (we call them “boulder catchers”) can trap 95% of larger particles but only 3% of very small particles.”
“Filters that claim to remove, say, 99% of pollen or mold are sometimes basing that on removing whole pollen or mold grains and do not factor in particle fragments (they break up into finer particles).”
Pleated filters pack more surface area into the same frame size as standard filters and thus are more efficient.
Many furnace filter manufacturers now use the expression "electrostatic" in their product descriptions. An electrostatically charged filter is better than a standard pleated filter with many contaminants, and they’re recommended for homes with allergy sufferers, smokers, or pets. The electrostatic charge is added during manufacturing. There is no requirement for a separate electrical supply. It's not something that needs to be re-charged.
A good furnace filter isn't expensive. However, it is difficult to give accurate prices because of the enormous variety of materials and sizes and the competitive nature of the furnace filter market.
As a rough guide, disposable furnace filters start at around $7or $8 each for 20x20x1. The price rises to between $15 and $20 for 20x30x4. MERV rating has little impact.
Washable filters, not surprisingly, are considerably more expensive. Expect to spend anywhere from $30 to $50 apiece, depending on construction.
Never run your furnace or HVAC system without the proper filter. Not only will it adversely affect your air quality, it will also allow dirt and dust into parts of the system that should remain uncontaminated. The result will be poor performance, higher bills, and breakdowns.
Filter quality and value depend on the application, including the size and airflow of the HVAC system. For example, the higher the MERV filter value, the better the dust removal – if your system can push air through it.
Running the HVAC system on continuous fan is the best way to clean the air regardless of the type of filter you use.
Less-efficient filters get more efficient as they load, since the pores begin to fill, spaces between the media fibers get smaller, and they start trapping finer dust. Of course, this also means the filters are clogging and will soon obstruct airflow.
How often you need to change the filter will depend on how efficient it is, how much you run the fan on your HVAC unit, and how many dust sources you have inside.
The best filters tell you the percentage of particles removed by size at a given airflow.
HVAC systems and filters are like vacuum cleaners. They should move enough air to clean the environment without allowing the dust to blow back into your home.
Q. What is a micron?
A. A micron (or micrometer) is one millionth of a meter, or 0.000039 inch. To give you an idea of just how small that is, a human hair is about 70 microns thick.
Q. What is the purpose of a HEPA filter, and are they best?
A. HEPA (high-efficiency particulate air) filters extraordinarily efficient, removing nearly 100% of particles as small as 0.3 microns. However, they have a very dense structure, and most furnaces don't produce sufficient pressure to drive air through them. If that's the case, all you're doing is blocking up your system and actually getting no filtration at all.
As our expert tells us, “A great filter is the most efficient one your HVAC system can handle while still moving enough air to make a difference.”
Q. How often do I need to replace my furnace filter?
A. It depends on a variety of factors. A standard, one-inch-thick filter should be changed after around 90 days, but thicker filters can last much longer.
If you have pets or are a smoker, your filters will become clogged more quickly. If you have breathing difficulties, you'll probably want to change them more often because you'll be more susceptible to airborne particles.
Your furnace or HVAC manual should give you the information you need. You can also get information from filter suppliers. Follow the instructions carefully.