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Is a dense, expensive air filter the best choice?

TL;DR – In a rush? Here’s everything we cover in this article:

  • Dense air filters can actually suffocate your AC system – If you look at the cross section of the thin, but dense (high MERV) AC filters, there’s a ton of filter material shoved in a one-inch frame. This pile up of filter material will stop your air flow – it's about as effective as using a piece of cardboard as a filter.
  • Just because it costs a lot of money, doesn't mean it's the best choice – It might come with a hefty price tag and some persuasive marketing promises in the sales pitch, but it might not be best for your particular AC unit.
  • So, what's the best AC filter to buy? – We recommend installing a media filter cabinet, where suitable. Their accordion style allows for a large surface area to collect all that unwanted dirt, dust and debris but enables a good, healthy airflow too.

A nice thick pleated air filter will stop all that nasty dirt and dust getting into your home's air supply, so it must be the best choice air filter for your AC right?

Wrong!

Dense, pleated, high-MERV air filters do capture a lot of pollutants, but they also reduce the air pressure in your system by restricting the airflow into your blower or furnace. This can increase energy bills and damage your HVAC system.

Air flow to your AC system is like blood flow to our circulatory system. When the flow is restricted the whole system suffers and if not dealt with, the system can die prematurely.

What is an air filter for?

When it comes to AC systems it’s all about air flow, air flow, air flow. You may think the air filter is for you, it is advertised that way, but an air filter’s #1 job is to keep your coil clean and prevent dirt and large particles from entering your AC system. A byproduct of this is that the filter removes those same contaminants (pet dander, bacteria, smoke, dust and dirt) from the air you breathe in your home. Win win.

So you have the perfect filter installed, great, no more worries… but what happens when you forget about changing out your filter regularly? By doing its job well, the filter gets clogged and the more clogged it gets, the less the flow of air your system gets to work with. As a result, the fan has to work harder to cool or heat your home, reducing efficiency – which means higher energy bills.

The air flow situation requires two things, the right filter and regular changing out of that filter when it is dirty.

This is why we nag about changing your filters regularly. Dirty and blocked filters starve your system of its air flow. Try running up a hill with your hand over your mouth and nose, your heart and lungs would have to work harder to get the airflow you need and you would tire out quickly.

So, what's the best choice of air filter for your AC?

This is truly a goldilocks situation, some don’t filter enough, some filter too much and some are just right. Finding that sweet spot for your system is the key. We don’t want you choosing a filter that actually damages your system.

First, let's look at the air filter rating system, MERV.

What is MERV?

MERV stands for Minimum Efficiency Reporting Value and is a scale of air filter effectiveness. It was created by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) to encourage better HVAC design and improved benefits.

MERV ratings range from 1 to 16. The higher the MERV rating, the more dust, debris and dirt that get caught in the filter. A MERV 16 filter will capture an average of 95% of the particles that pass through it.

High MERV filters

Just based on the information above, a high MERV filter sounds fantastic! Well, there is more to the story. There are different thicknesses of filter. You can have a 1” super high MERV filter that is so dense that it captures a lot but also restricts a lot – especially when it gets dirty. This filter is very efficient at one part of its job (capturing contaminants) and utterly fails at the other part (air flow).

Filter your air WITHOUT restricting the air flow to your system

Does this mean that you should never get a high MERV filter? No way, you just need the right kind of high MERV filter for your system. If your system setup can take a thicker filter, commonly referred to as a media filter, that is the best choice. A media filter is 4-5 inches thick and has more filter material surface area due to its accordion design. It still captures a lot but does not restrict air flow. Some systems can be retrofitted with a media cabinet to accommodate the size of a media filter. Ask your ac contractor if this is an option for your ac system.

Media filters, due to their increased surface area, have these extra benefits:

  • Higher dust-holding/capturing capability without blocking airflow
  • Longer life/less maintenance – most pleated 4-in/5in media filters will last between 6-12 months between changes (varies based on pets, quantity of people in the home and household contaminants)

What if my system won’t accommodate a media filter?

If a media filter doesn’t work for your system configuration, check your HVAC manual for recommendations. Get the filter they suggest and change it regularly (every 1-3 months). In most cases a cheaper 1” 6 MERV filter will work well – just change it often.

Remember, low airflow = wasted energy.

Problems with retrofitting an AC system with a media filter cabinet mainly has to do with space. If your system is in a tight closet, it might not fit. Contact us to evaluate your AC system configuration to see if a media cabinet is right for you.

Tips on changing your air filter

  • Once you choose a filter that works best for your system:
  • Take a photo of the packaging/sku for ease in finding the same one again. The filter aisle can be overwhelming. You think you will remember the size, but you probably won’t.
  • Test how long it takes to get dirty, usually once a month for 1” pleated and once every 6-12 months for media filters. Check often, this may change depending on the season. Once you have the typical timeframe, you can set a reminder.
  • Store filter details. Put the details of the filter in your phone contacts as “Air Filter” or in a notes app, filled under home maintenance
  • Set your smart thermostat app. Some smart thermostats let you control the temp from your smartphone, some of these apps also have a reminder and alert function.
  • Set a reminder on your phone. In the form of an alarm (with a description), or make a recurring calendar event that includes the make/model/size and quantity needed. If you buy online, add a purchase link in the calendar reminder. Make sure the reminder has an alarm or alert of some type. You may want to add another one a week later “did you change the air filter?”
  • Associate changing the filter with another monthly chore, like paying your energy bill.
  • Stock up, buy enough filters to last you a year. This removes a barrier of shopping for filters. Have supplies on hand to changing your filters often.
  • Mark the month on the side of each frame. And store the filters somewhere they will be seen, like the laundry room, utility closet next to cleaning supplies.
  • Put a sticky note on the final filter to remind you to make another order. You then can take that sticky note and put it by the shopping list.
  • Sign up for our maintenance plan and purchase the filters in advance, we will change them for you as part of your checkup

Do you want cleaner air than a filter can provide?

If you’re really interested in keeping your air clean, we’d suggest you get an air cleaner/purifier installed. There are also UV air scrubbers you can install in the plenum. Indoor air quality is not a one-size-fits all situation and should be customized for your home, but either of these devices will certainly improve the air you breathe inside your home.

Final thoughts: For the best AC filter for your needs, ignore the price tag and the manufacturer’s marketing and check your HVAC manual for recommendations or talk to a professional, like us. Our Nichols & Phipps service or installation technicians can help you answer this plaguing filter question.