Air Filter Buying Guide: Why Size and Efficiency Level Matter

HVAC Logo IconBy HVAC.comJanuary 25, 2024

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Be Cautious of High-Efficiency Filters, Which Can Cause More Harm Than Good

One of the most important tasks you can perform to maintain your HVAC system is to regularly change out the air filter. However, it’s not just about changing the filter – it’s about choosing the right filter for your specific HVAC system. Not all filters are created equal, and some high-efficiency filters – including HEPA filters – may actually do more harm than good for your system.

So, how do you choose the right air filter? HVAC.com dives into the details and explores the factors you should consider when selecting an air filter for your HVAC system.

Finding Your Filter Size

Size matters when choosing the right air filter for your HVAC system. Finding the right size air filter is important to ensure the filter fits properly and performs efficiently. Air filters come in many sizes, and various HVAC systems require filters of varying dimensions – you can’t simply pick one up at your local big-box store at random.

Using the wrong size filter can lead to a range of issues that affect the efficiency and functionality of the system. Filters that are too small may allow dust and debris to bypass, circulating throughout the system and reducing indoor air quality. Filters that are too large may not fit properly, leading to gaps and bypass airflow, allowing contaminants to enter sensitive components.

It’s essential to check the owner’s manual for filter specifications before purchasing replacement filters. The manual will tell you the appropriate size filter for your HVAC system. If you cannot locate this information, look at your existing air filter to determine the size you need:

  1. Find the existing filter in your HVAC system. It is usually located in the return air duct or near the furnace or air handler.
  2. Look for the size information on the side of the filter frame. The size is typically printed on the cardboard edge of the filter.
  3. If the size information is not visible, use a tape measure to measure the length and width of the filter. Measure the length (top to bottom), the width (side to side), and the thickness in inches.
  4. Write down the measurements. For example, if the measurements are 20 inches by 25 inches, record it as 20" x 25" x 1”.

Pleated Vs. Non-Pleated

For the most part, pleated furnace filters are more efficient and last longer than simple fiberglass non-pleated filters. Pleated filters contain much more surface area to catch pollutants/contaminants and have the ability to have smaller pores to capture smaller particles while still allowing full air flow.

Air Filter Efficiency

When it comes to measuring air filter efficiency, a rating system called MERV (Minimum Efficiency Reporting Value) is used. This system rates filters on a scale from 1 to 20, with higher numbers indicating better particle removal efficiency. Filters with a higher MERV rating tend to cost more than less efficient filters.

It’s essential to note that air filters with a higher MERV rating may not be appropriate for use with your furnace. Depending on your unit, a high MERV rating can be too restrictive and may affect your HVAC system’s overall performance.

  • Filters with higher MERV ratings typically have denser materials designed to trap finer particles. However, this density can lead to increased resistance to airflow. If the filter restricts airflow excessively, it can strain the HVAC system, causing reduced efficiency and potentially leading to overheating.
  • The higher resistance to airflow caused by a high-MERV filter can force the HVAC system to work harder to maintain the desired temperature. This increased workload results in higher energy consumption, leading to elevated utility bills.
  • Strain on the HVAC system caused by restricted airflow can contribute to premature wear and tear on components such as the blower motor and the fan. This can cause more frequent breakdowns and a shortened overall lifespan of the system.
  • A filter with too high of a MERV rating may impede the flow of conditioned air into your living spaces. This can result in uneven heating or cooling and decreased comfort levels throughout your home.

To avoid these issues, it’s essential to choose an air filter with a MERV rating that aligns with the recommendations of your HVAC system’s manufacturer. Most residential HVAC systems work well with filters in the MERV 8 to MERV 13 range. Higher-rated MERV filters should only be used with systems designed to accommodate such filters.

Is a HEPA Filter Worth It?

HEPA stands for High Efficiency Particulate Air filter, and it’s made up of densely packed layers of fine mesh. These filters are designed to trap tiny particles like dust, pollen, and even bacteria. In fact, they’re so effective that they’re often used in hospitals and clean rooms. You’ve probably heard of them before, and you may be wondering if a HEPA filter is worth it.

HEPA filters have a very high MERV rating, typically around 17-20. While that may sound impressive, it also means that they can be too restrictive for most residential HVAC systems. In plain English, HEPA filters are too good at their job, and they can make your HVAC system work harder than needed. This can result in decreased airflow, which can lead to issues like frozen coils or even system failure.

While HEPA filters may be worth the investment in certain situations (such as in a hospital or laboratory), they’re generally not recommended for use with a standard furnace in a residential home.

Media Air Cleaners

If you want the power of a high-efficiency filter, installing a media air cleaner may be an option. These units use thicker filters with a MERV rating between 13 and 16, which means they can capture even smaller particles like pollen, mold spores, and pet dander.

While they work with most residential systems, some units may not be able to handle the increased airflow resistance that comes with a high-MERV filter. To avoid damaging your HVAC equipment, it’s best to check with a licensed contractor before purchasing a media air cleaner. They will be able to assess your system and recommend the best option for your needs.


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