What You Need to Know About Your HVAC Filters

In a previous blog post, we answered a few common HVAC questions that our customers ask us. Several of these have to do with furnace and AC filters, which must be periodically changed out to keep HVAC equipment safely operating at peak efficiency.

The problem with HVAC filters is that there are almost too many replacement options to choose from, which vary widely in quality, capability, and—perhaps most importantly—price. Yet responsible home comfort system owners have to make that choice at least once per year, and typically much more often. Finding the filters that work best for your system can require a lot of research and shopping that most people don’t have the time or interest to do.

Today’s post hits the high points about HVAC filters that you absolutely must know as an equipment owner, and also shows you why it’s often best to rely on professionals to replace your filters as part of regular preventative maintenance.

Changing your filter regularly is a must for protecting your system

HVAC professionals often preach the gospel of routine maintenance for your heating and cooling equipment. This is because regular system checks and tune-ups—including filter changes—prevent messes, increase safety, and ultimately save you money over time by guarding against catastrophic equipment failures.

How? By keeping damaging dirt and debris from reaching your equipment’s mechanical parts. Filters do this vital job by putting a physical barrier between the air flowing through your system and things like your furnace or AC unit’s hardworking motor.

In fact, did you know that filters exist more to protect your equipment and keep ductwork clean than significantly improve indoor air quality? It’s true that filters help keep dirt, dust, and pollutants from circulating through your system, which prevents them from being distributed into the air you breathe, but HVAC filters are not designed to change the air quality in your home drastically.

Think of it this way—your AC or heat is only running part of the time, often for just part of the year. When equipment is on standby between cycles, it’s not actively filtering your air. This is why, if you have allergies or sensitivities to pollutants, you may want to consider separate, always-on equipment to clean and purify the air in your home.

How often should you change your HVAC filter?

The frequency at which your HVAC filter should be changed out will vary based on the type and thickness of filter that you use. As we talked about in that previous blog post linked above, filters come in a variety of thicknesses between about 1” and 5” with different filtering abilities based on the materials they’re made from. This is our recommended change interval advice:

  • One or two-inch thick filters – change at the start of each season, and then every 3 months during your equipment’s operation.
  • Three to four-inch filters – change two times per calendar year, when you make the switch between heating and cooling (April/May in our home service area here in Lancaster County, PA) and back again (October/November).
  • Five-inch filters can be changed once per year.

Generally, you won’t need to change thicker filters as often as thinner ones since they can hold more dirt, pollen, and dust before becoming clogged. That said, just buying the thickest filter you can find isn’t the best idea (more on that in a moment)—there are many factors to consider related to your particular HVAC system, as well as how you live in your home.

Choosing the right filter can be daunting—you have many options

The goal is never to allow your filter to be totally clogged so that air can’t easily pass through—this situation may cause your HVAC system to malfunction or even shut down completely. However, there are hundreds of different filter options on the market today, and not all of them will be suitable for your equipment.

Understanding MERV ratings

Before considering filter types, it’s essential to understand their main efficiency rating system developed by industry association ASHRAE and abbreviated as MERV—Minimum Efficiency Reporting Value. This number can be found on filter product packaging to give consumers and professionals alike a way to know the size and type of contaminants that a particular filter can remove from the air. The higher the MERV rating number, the more—and smaller particle size of—pollutants the filter can trap.

Fiberglass filters

With MERV ratings at the bottom end of the scale (expressed in numbers between 1 and 20), usually between about 1-4, spun fiberglass filters tend to be the lowest priced. They can trap most pollen, dust mites, carpet fibers, and dust from woodworking activities.

Disposable Pleated filters

Generally made from paper or polyester materials mounted in a cardboard frame, pleated filters often feature MERV ratings of 5-7. These filters can keep finer pollutants, like cement dust, pet dander, and aerosolized sprays, out of your HVAC equipment and the air it circulates.

Box and Bag filters

Made from a variety of materials including paper and “microfine” fiberglass, so-called box and bag filters are rigid in their construction and provide superior level filtration (with MERV ratings between 9 and 16) for home use. Also sometimes referred to as cartridge-style filters, these types are often specially designed and recommended by equipment manufacturers.

Permanent electrostatic filters

If you’re a DIY-er who likes to save money by making things yourself, these “washable” filters could be a good choice. Though these filters may not be compatible with your equipment (always check with your HVAC system’s manufacturer), permanent filters only need to be replaced every few years—you just clean them out and put them back into operation at regular intervals instead of throwing them away each time.

HEPA filters

As we’ve talked about in the past, HEPA filtration is the most comprehensive level available with MERV ratings at the highest end of the scale. Unfortunately, a lot of home HVAC systems are not designed to work with these advanced filter media and can actually be damaged from the reduced airflow they cause. If you believe you need HEPA-level filtering, talk with your professional HVAC service company to consider your options.

Beyond MERV ratings: Understanding MPR & FPR

While the MERV rating system was designed to be an impartial reference guide, there are other rating systems for filter performance that you may encounter. MPR (Microparticle Performance Rating) & FPR (Filter Performance Rating) are the most prominent alternative scales for measuring filter effectiveness.

While we don’t have time today to dive deeply into the differences between these metrics, know that MPR is proprietary to 3M, the largest 3rd party manufacturer of filter products. FPR is also a proprietary system that was developed for The Home Depot. Confused? Your best bet is to call on HVAC professionals to help you cut through all the abbreviations and marketing to find the right filter!

Save time and frustration—let Comfort Aire take care of your HVAC filters!

Here at Comfort Aire Heating & Cooling, we are those qualified HVAC experts who can help you with all of your filter maintenance needs. We’ve been making Lancaster County a more comfortable place to live since 1995.

Give us a call today to talk about our no-hassle preventative maintenance plans, and stop worrying about your HVAC filters and equipment.

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