Air filters

How to Select the Best Air Filter for Your HVAC System

An air filter is made by layering materials such as spun fiberglass, paper, or cloth, which is then used to capture particles from the air passing through the filter. This keeps those particles out of the air you breathe. In addition, it prevents larger particles from collecting inside your heating system’s internal components, which improves the performance and longevity of your system.

Air Filtration vs. Airflow Restriction

There is, however, a tradeoff for better air filtration. Regardless of the size and efficiency rating of the air filter you use, the filter will cause some restriction in airflow.

What does this mean? When there is a restriction in airflow, the volume of air crossing the heat exchanger in a furnace will be reduced.

If you have a basic air delivery system, the fan motor will slow down and move less air across the heat exchanger and air conditioning coil. This will fatigue the motor over time.

If you have a variable-speed motor air delivery system, the fan motor will speed up to overcome the resistance. Simultaneously, the motor will consume more electricity and possibly overheat, resulting in fan motor fatigue and potential failure if the resistance is too high for too long.

When you restrict the airflow across a heating system, the heat in the heat exchanger will build up and potentially exceed the designed maximum temperature. When the heat exceeds the designed maximum temperature, advanced fatigue begins to set in.

What Components Are Affected?

System components that can be damaged include blower motors, inducer fan assemblies, high temperature limit safety devices, and heat exchangers. When a heat exchanger exceeds the designed maximum temperature, the heat exchangers will plug up or even crack so that exhaust gases containing carbon monoxide may be released into your home.

How Can I Protect My HVAC Equipment?

As a homeowner, your best practice is to install an electronic air cleaner. If you decide to use a disposable air filter, consider using a 4-inch MERV 8 or MERV 10 air filter, replacing the filter every 90 days.

To ensure proper airflow, keep all your floor or ceiling registers open, do not block your registers with furniture, and do not install filters at the registers.

Also, be sure to schedule safety and energy efficiency inspections as well as annual preventative maintenance to be performed by a professionally trained technician.

What Are MERV Ratings?

In your home, air continuously circulates through the ductwork and passes through the air filter each time it cycles through. Minimum Efficiency Reporting Value (MERV) is the measurement of how well a filter can remove particulates from the air. The MERV rating test measures a filter’s efficiency by the percentage of particulates it can capture in a single pass.

MERV 1–4 filters are like the examples shown below. The poly-type material is close to MERV 1 rating. This filter is extremely porous and is intended to protect the comfort system from large objects and particulates. This filter will not reduce dust in a home because 90 percent of particulates or more will pass right through it.

The hog hair example is a MERV 4 rating. This is a washable material that will stop large particulates but will not stop fine dust and other common allergens. When lower MERV-rated air filters are installed in the ductwork, advanced cleaning and maintenance will be required more frequently due to their poor filtering capabilities.

If you have air conditioning, your equipment may require chemical cleaning annually or biannually. This will dramatically increase the overall cost of ownership for your system.

Poly/Hog hair filter MERV 1MERV 4

MERV 5–7 filter media changes to a different style of material. Pleated air filters are made of paper, polyester, or cotton materials. These materials are folded into an accordion shape and housed in a cardboard frame. These air filters may have cardboard crossing the filter media in an x-pattern to hold the pleats in place. The folds and pleats increase the surface area of the filter to capture even more particulates.

MERV 8–13 filters will remove approximately 80 percent of the particulates in the range of 3.0 microns, which includes fine dust particulates and larger pollen particulates. The back side of the air filter typically has molded wiring to support the air filter media.

MERV 14–16 filters are specialized air filtration systems. These are designed for hospitals and industrial facilities. These filters are customized to work with the air delivery system they will be paired with. If you add this filter to your average residential comfort system, there is a very high chance that this will damage the comfort system.

Furnace Filter Thickness

Pleated air filters are available in 1-inch, 2-inch, 4-inch, and 5-inch thickness. These filters are available in the most common sizes.

Why is a 5-inch air filter more effective than a 1-inch air filter with the same MERV rating?

If the filters were removed from the cardboard frame and stretched out to full length, you would see that the 5-inch filter is much longer than the 1-inch filter. When compared to the 1-inch air filter, the 5-inch air filter dramatically increases the surface area for collecting particulates.

Another benefit of having a greater volume of surface area in an air filter is that the air filter will last longer without requiring replacement.

Electrostatic Filters

An electrostatic air filter uses an electrostatic charge to attract and trap particles like a magnet. There are both disposable and washable electrostatic filters.

These air filters are made from a very tightly woven material. At their cleanest, electrostatic air filters will substantially restrict airflow. After the air filter has been installed for a while and it becomes filled with dirt and dust, the restriction in airflow will increase.

All Weather does not recommend using electrostatic air filters due to their restriction of airflow and the associated safety risks previously described. If, however, you decide to use an electrostatic air filter, the installing contractor must increase the size of the return ducts as part of the overall ductwork design.

Activated Carbon Filters

The carbon particles in an activated carbon filter are capable of trapping gases, odors, and particles within its pores. This class of air filter can also trap volatile organic compounds (VOCs). Thus, activated carbon filters are frequently chosen by homeowners who want to reduce smoke, pet odors, and other unpleasant indoor smells.

UV Filters

Ultraviolet (UV) filters are used in homes to complement a paper filter or an electronic air filter. UV filters can kill microbes, bacteria, and viruses that are circulating in the air by using ultraviolet light.

If someone in your home has a compromised immune system, a UV filter may help protect their health by improving air quality.

Reusable/Washable Air Filters

If you are conscious of environmental impact and/or your budget, reusable filters may appear to be the best option.

However, these filters tend to be better in concept than in practice. Washable filters are made from plastic or metal, which are durable materials, but they are not the most effective materials for filtering particulates from air.

It can also be challenging to thoroughly clean and dry the filters before returning them to the ductwork.

HEPA Air Filters

High-efficiency particulate air (HEPA) qualified filters must be able to trap at least 99.97 percent of particles in the air that are 0.3 microns. HEPA air filters were originally developed by military scientists during WWII as a method to capture radioactive air particles when testing the atomic bomb.

HEPA air filters are made of interlaced fiberglass that is tightly woven together into a filter media. As particles pass through this type of advanced air filtration, they are eliminated by diffusion, direct impaction, interception, or sieving. HEPA air filters are great for families that deal with allergies, asthma, or other respiratory illnesses, but the price is going to be higher than types of air filters.

HEPA Air Filters Versus AccuClean Electronic Air Filters

Although HEPA air filtration is the best available option, the cost of installation and year-round maintenance can make it less viable for many households. A good alternative is the American Standard AccuClean Whole-Home Air Cleaner, which has a lower cost of ownership and a lower initial investment price. Below is a list of pros and cons to help you compare these two options.

HEPA Pros

Removes 99.98 percent of all particulates out of the air.
Includes a 1-year factory warranty.
Can be installed remotely from the heating system.
Can be installed after the fact if you have a newer comfort system in place.

HEPA Cons

Requires replacement of filters on a semiannual basis.
Non-communicating on the timing of air filter replacement requirements.
Filters a small sampling of the air flowing through the air delivery system.
Takes a lot of space in the mechanical area for the filter box and the ductwork modification.
May require an electrician to bring a plug-in receptacle if one is not located within 6-feet of the unit.
Requires a secondary disposable air filter that requires replacement on a semiannual basis.
Sends materials to the landfill 4-6 times a year.
Requires higher cost for replacement materials due to shipping cost.

AccuClean Pros

Removes 99.98 percent of all particulates out of the air.
Does not require replacement parts or filters.
Communicates filter cleanliness via an LED display.
Includes a 10-year factory part warranty.
Filters 100 percent of the air flowing through the air delivery system.
Includes easy-to-wash parts.
Sends fewer materials to the landfill, such as disposable filter.

AccuClean Cons

Requires enough space to install in the ductwork, which may not work for all applications.
Incurs higher costs when not installed at the same time as a new comfort system.

Let All Weather Assist With All Your Air Filter Needs

All Weather is happy to assist with any of your HVAC needs for your Snoqualmie, WA, home. Give us a call today at 425-463-9814 or request service online.

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