Furnace filters aren’t the most glamorous topic, but they are absolutely vital to your health and the health of your HVAC system. The right filter will help keep everything running smoothly by filtering out particles. These particles can be bad for your health, particularly if you have allergies, but they can also take a toll on your HVAC system. This is why selecting the right filter and replacing or cleaning it as directed is so important.
The History of Furnace Filters
Technically speaking, a furnace filter is a removable filter that is positioned somewhere between the air intake and the motor and heating coil of the unit. When furnace filters first came into use, indoor air quality wasn’t a consideration. There simply wasn’t an awareness of the issue and its impact on the resident’s health. It was solely designed to protect the HVAC system, not the people inside the home.
It was recognized that particles like dust and other contaminants got into the air. It was also recognized that if this debris were allowed to build up inside the system, that it would reduce efficiency and eventually cause the unit to malfunction. The fiberglass filters you see today are essentially the same as these first filters. Designed to keep some of the largest and most damaging particles out of the HVAC system.
As time went on, air quality became a concern. Consumers began to recognize that there was a direct link between how healthy the air was, and how healthy they were. Manufacturers saw this and began creating filters that took air quality into account, by designing them to filter out common particles.
The MERV rating system was launched in 1987 by the American Society of Heating, Refrigeration, and Air Conditioning Engineers. This was the first system that allowed for a standard performance rating other than HEPA filtration.
Before we get into comparing the different types of filters, it’s important for you to know about their rating system. This is known as MERV (minimum efficiency reporting value). The MERV value can vary from one specific filter to the next. However, different types have their own range of MERV ratings. The MERV rating measures the size of particles the filter is able to capture, with a higher number indicating it collects smaller particles.
Is Higher Better?
IN terms of air quality, yes. However, there are other considerations as well. MERV ratings range from 1-16. For home use, most fall between 8-11. If you have allergies or asthma, a MERV rating of 12 will stop common allergen particles. As the MERV rating goes up, airflow goes down. This has an impact on efficiency. The furnace has to work harder to produce the same airflow. In many cases, this effect isn’t very noticeable with standard home air filters. However, if you switch to a higher rated filter and you find your energy bills increasing significantly, you may want to take a closer look.
MERV vs MPR and FPR
MERV isn’t the only performance rating that you might run into when shopping for a furnace filter. Different companies have different rating systems. They are all based on the size of particles the filter is able to capture. There are 3 basic grades of filters that can give you an idea of what quality you need no matter which rating system is used.
Fair performance filters will catch pollen, large dust particles, carpet fibers, mold, spores, and cement dust. They block particles from 3.0–10.0 μm.
The ratings for fair performance are:
- MERV 8
- MPR 1000
- FPR 7
Good performance filters will catch smaller particles. This is usually enough for the average homeowner to ensure good air quality. Particles trapped include large bacteria, auto emissions, smaller dust particles, and pet dander. It traps particles up to 1.0–3.0 μm.
The ratings for good performance filters are:
- MERV 11
- MPR 1900
- FPR 9
High-performance filters will catch even smaller particles. These filters are the best home filters in terms of air quality, but they will have an impact on the efficiency of your HVAC system. They catch smaller bacteria, sneeze droplets, smoke from tobacco or cooking, and smog. They catch particles as small as 0.3–1.0 μm.
The ratings for high-performance filters are:
- MERV 13
- MPR 2200
- FPR 10
Disposable vs. Permanent
Several types of filters can be purchased as disposable or permanent. Each has its advantages and disadvantages. Permanent filters will be much sturdier, often made with stainless steel or aluminum. They are usually designed to last for 5-10 years, however, some come with a lifetime warranty. The initial cost is more expensive, but it will save you money over the life of the filter compared to buying disposables for that time period.
Permanent filters must be washed, usually once a month. Disposable filters are simply replaced either every month or three months. Disposables are more convenient because you don’t have to wash them. However, you do have to continue to purchase them, which is a task as well.
There are a few situations in which a permanent filter might make more sense than a disposable. The first is if your filter is a size that is difficult to find. If your local store doesn’t carry your size, purchasing a new one every month becomes more of a hassle.
If you are concerned about the cost of air filters, particularly if you need a high MERV rated filter, permanent filters can bring you significant long term savings.
Lastly, if you have severe allergies, asthma, lots of dust, or pets in the home, you may prefer a permanent filter. Replacing filters costs money, so most people wait until they absolutely have to replace them to do so. While this is understandable, it also reduces the filter’s effectiveness. Permanent filters simply need to be washed and replaced, which you can do as often as you feel the need to, without spending extra money.
There are some excellent disposable filters on the market today, and most people prefer the convenience of disposable. Higher quality filters that only need to be replaced every 3 months are still disposable, but they can offer you added the convenience of having to deal with it less often.
Types of Filters
The different types of filters are:
- Fiberglass filters
- pleated filters
- electrostatic filters
- carbon filters
- HEPA filters
Fiberglass filters are the cheapest filters you can buy. They are made from spun fiberglass. They offer very little air resistance. However, they often have a MERV rating as low as 2-3. They are a good choice for those whose homes aren’t very dirty and who don’t require the cleanest air. If you have issues with dust, own pets, or are concerned about air quality, fiberglass filters aren’t the best choice for you.
- High airflow
- Low MERV RATING
- Can release particles into the air upon removal
Pleated filters are designed with pleats that aid in filtration because it provides a greater surface area. They are normally made from polyester or cotton, which is woven tightly. Fiberglass filters are woven loosely enough you can see through them, pleated filters have a solid appearance. They have MERV ratings ranging from 6-12, depending on how tightly they are woven together.
Pleated filters are more expensive than fiberglass filters, but they are much more effective at cleaning the air. Some are specifically designed for those with allergies or pets, and these will have a higher MERV rating.
Pleated filters are more expensive than fiberglass filters. Generally, the higher the MERV rating, the more expensive the filter will be. However, many pleated filters only need replacing every 3 months under normal conditions, which can mitigate the expense somewhat.
The average person without allergies will probably be best served with a pleated filter with a lower MERV rating to balance clean air with HVAC airflow. For those who need greater filtration, the higher rated MERV pleated filters are an excellent choice.
- Higher MERV rating
- Can last 3 months
- More expensive than fiberglass
- Reduced airflow can strain HVAC
Electrostatic filters can be washable or disposable. Disposable electrostatic filters are usually pleated. Washable electrostatic filters are often made from polypropylene, which is a type of plastic. Electrostatic pleated filters are made from cotton or polyester. These filters charge the dust particles and then draw them into the filter like a magnet.
The washable filters may have multiple layers that need to be taken apart and cleaned. Be careful not to use high-pressure water when cleaning, because it could damage the filter. You should also not assume it doesn’t need cleaning because you don’t see a lot of dust on the outside, as these are designed to draw the dirt deeper. The washable electrostatic filters are usually thicker as well. This can cause strain to your HVAC system because of reduced airflow.
It’s not clear whether electrostatic filters are really “worth it”. You can find non-electrostatic filters with the same MERV rating, so it seems to be more a matter of personal preference.
- Available as washable or disposable
- Traps dirt deeper into the filter
- Reduced airflow
- Washable filters may require more cleaning
- More expensive
Carbon filters use carbon, or charcoal, to filter the air. Carbon is very effective at trapping gases. The pollutant molecules stick to the carbon molecules in a process called adsorption. This differs from absorption. A sponge is an excellent example of absorption. Water is soaked into the sponge, essentially becoming a part of it. With adsorption, the water would stick to the sponge-like a magnet instead of being absorbed into it.
Each carbon molecule only has so many open adsorption sites. When they are full, it will no longer catch the pollutant particles. In fact, it will release particles with less affinity for its sites and catch particles with more affinity, releasing pollutants into your air. If you notice a carbon filter giving off a smell, this is why.
One of the downsides to carbon filters is that it’s difficult to know when you need to change it. You won’t see a lot of visible dirt on the filter. Your best bet is to follow the manufacturer’s recommendations for when to change it. Do not wait for it to look like it needs to be changed, because it won’t. If you wait for it to smell, then it’s already releasing the chemicals you wanted to avoid back into the air.
Choosing a Carbon Filter
When choosing a carbon filter, it’s important to look for one that is activated and has a high carbon content. Activation is a chemical process that actually increases the surface area of the carbon molecules, making them more effective. Carbon content is, of course, how much carbon is actually in the filter. The more carbon that’s in the filter, the more pollutants it will be able to absorb.
Thickness is a consideration as well. Thicker carbon filters will be able to capture more particles than thinner filters. This is because the air spends more time in a thicker filter. This is known as dwell time.
Is a Carbon Filter Right For You?
Carbon filters are great for filtering out some types of pollution, but they aren’t very effective at others. They are excellent at removing VOCs, or volatile organic compounds. Carbon filters are excellent at removing cigarette smoke, fumes from cleaning products or drying paint, and car exhaust. They are not very good at removing particles like dust or pet dander, however. If you live in an area with high air pollution, smoke in the home, or have recently remodeled, a carbon filter might be a good idea. If these situations don’t apply, you and your HVAC system will likely benefit from a pleated filter with a higher MERV rating.
- Removes VOCs and other pollutants that other types of filters cant
- Doesn’t remove smaller particles like dust or bacteria
- Difficult to know when to change
- Can release chemicals back into the air
HEPA stands for HIgh-Efficiency Particulate Air. A true HEPA filter has a MERV rating between 17-20. However, the density of the filter required for this level of filtration is not suitable for your home HVAC system. It would severely affect efficiency, and possibly even damage your unit. If you feel the need for HEPA filtration, you will be much better served to get a filter system that is separate from your furnace.
Some pleated filters come close to HEPA levels and are suitable for home use. They have a MERV rating of 13. If you have severe allergies or asthma, you may benefit from this type of filter. For most homes, even those with allergy sufferers, a MERV rating of 11 is suitable and gives you the best trade-off of filtration vs proper airflow.
- Filters microscopic particles including viruses
- Not suitable for most HVAC systems
Which Type of Filter is the Best?
Each type of filter has its pluses and minuses, and the best is certainly a subjective term. Best for what? Here’s a rundown of the best furnace filters for some common situations.
Best for Budget
Fiberglass filters are certainly the most budget-friendly. They are so cheap that they far surpass even washable filters. However, keep in mind that this is the only area where they excel.
Best for Average Household
Your average household will do best with a pleated filter with a MERV around 11. This allows it to filter out most allergens without restricting airflow too much.
Best for HVAC System
The best filter for your HVAC system is probably a pleated filter with a MERV rating around 7. This will filter out the particles that could harm your system, while minimally restricting airflow.
Best for Air Pollution
Carbon filters are the best for removing air pollution, followed by pleated filters with a MERV rating of 13. If you are exposed to high levels of smog, cigarette smoke, or recently remodeled, carbon filters are a good choice.
Best for Severe Allergies and Asthma
A pleated filter with a MERV rating of 13 is the best for someone with severe allergies and asthma that’s suitable for a residential HVAC system. This should remove all the irritants from your air. If you require even higher levels of filtration, purchase a stand-alone HEPA air filter system.
Now that you know all about furnace filters, you are well equipped to select the best one for your needs. Don’t forget to wash or change your filter as needed for maximum performance.