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Revised:
November 23rd, 2020
What’s In a Furnace Filter
Filters are one of those things that every homeowner has and has to think about, but most don’t give it more than a passing thought. After all, if you replace your filter regularly, that’s all that matters, right?
Replacing your filter on time is indeed important, but it’s not the only thing that matters.
Why do filters matter? A lot of reasons:
- Improved air quality improves your health. This is particularly true for anyone with serious allergies or other respiratory issues.
- A functioning filter can keep your home cleaner, with less dust and pet hair.
- Air quality is directly linked to filter quality.
The facts below will talk about each of these three areas, and how filters can contribute (positively or negatively) to each one.
Facts and FAQs
We’ve listed a bunch of facts and frequently asked questions (FAQs) below.
For several of them, we’ve included a follow-up section on why a particular answer matters or what you should do next to ensure the best air quality for your home. These are the takeaways that will allow you to make more informed decisions for future HVAC installations and filter replacements.
Without further ado, let’s jump in.
Basic Filtration Terms
I wish we could have fewer acronyms in heating & cooling, but there are a couple that are good to know when it comes to filter efficiency.
What is CADR?
CADR stands for Clean Air Delivery Rate. It measures the cubic feet per minute of air that has had all the particles of a given size distribution removed. For example, if a filter has a 290 for a particular particle type, it will reduce those particles to the same level as would be achieved by adding 290 cubic feet of completely clean air per minute.
What is MERV Rating?
MERV stands for Minimum Efficiency Reporting Value. It measures a filter’s ability to capture particles between 0.3 microns and 10 microns, a microscopic unit of size measurement.
Is CADR or MERV Better?
Neither is the better gauge of effectiveness. Both measure slightly different things, and will generally increase as the filter improves. Importantly, though, neither is a complete assessment of a filter’s quality.
Types of Filters and Pricing
What filters are available to you, how much do they cost, and why would you want one over another? We tackle those below.
What’s an Entry-Level Furnace Filter?
An entry-level filter is generally made of fiberglass material and has a CADR of 10-12. They are usually thin (one-inch) and are cheaper than other filter options.
What’s a Mid-Range Furnace Filter?
Filters that are thicker and/or have higher CADR and MERV values will be the next step up from an entry-level filter. These generally come in four-inch models, can have MERV ratings up to about 18 and CADR at or above 200. Here at Fire & Ice, we often install Aprilaire four-inch filters, because they offer a nice mix of affordability and effectiveness.
What’s a High-End Furnace Filter?
Various companies have their own versions of high-end filters. They can have MERV ratings up to 20 and CADR ratings up to 1,200. Here at Fire & Ice, we sell the Trane CleanEffects. It’s more expensive than other options, but it’s washable. This means it doesn’t need to be replaced like other filters and can actually save you money over time.
What About Electric Filters?
These aren’t as popular anymore but do still exist. Some electric filters can reach up to 700 CADR, so they can be very effective. You’ll want to check to make sure they don’t produce unhealthy levels of ozone, but the best versions keep ozone levels to negligible levels.
Do Filters Come With Carbon Inserts?
Some do, yes, and this can be a good way to eliminate odors caused by smoke, cooking, or pets. As we’ll talk about in a bit, you’ll want to be careful that a carbon insert doesn’t block airflow, which can be damaging in other ways.
How Much Does a Furnace Filter Cost?
Entry-level filters can be purchased for as little as $20-$30 at department stores or online. Mid-range filters that last longer and capture more can run $50-$100. The most sophisticated filters are reusable and are many times more effective than standard filters. Filter and installation for these can run as much as $1,600.
Why Would I Want the Most Expensive Furnace Filter?
It seems hard to justify spending over $1,000 for a filter, doesn’t it? But let’s look at the numbers. Say you spend $1,500 on the installation of a high-end filter when you have a new furnace installed. That washable filter could last you 10-15 years, and could easily be saving you $100 per year in replacement filter costs. So already you can see how a high-end filter can pay for itself.
But that ignores the real reason you’d want to have one: air quality. If you have severe allergies, lots of pets, or are immunocompromised in some way, this can be the difference between breathing easy and having a home that actively fights against your immune system.
Installation, Replacing, and Using Filters
Knowing when and how to change your filter is important so that you can stay proactive in maintaining your system.
Is a New Filter Included at Installation?
Yes, it is for us, and it should be with furnace installation from any reputable HVAC contractor.
Where Is the Filter Loaded?
This is one where it depends. Usually, filters are side-loaded near the base of the return air drop. This allows the filter to catch and filter the air that’s returning to your furnace from your home, to be heated and recirculated throughout the home. Other times, the filter is bottom-loaded. Consult your user manual or speak with your HVAC partner if you have any questions on this.
Can I Replace Filters On My Own?
Yes, a homeowner can always replace their own filter, though some people like to schedule filter changes to coincide with regular equipment maintenance. This takes the guesswork out of when to replace them, and saves you the hassle of having to remember to do it.
ALSO READ: How, Why, and When to Change Your Furnace Filter
When Should I Replace My Filters?
A recommended schedule will come with the filter. It’s usually 30-60 days, up to about 6 months for some filters. However, if you have a lot of pets or smoke, you may have to replace the filter more frequently.
On the other hand, if you don’t use your systems for several months out of the year, occasionally filters can outlast their expected lifespan.
Static Pressure and System Performance
Filters affect your system’s performance, up to and including complete system failures. Let’s look and why and how this happens.
What Is Static Pressure?
Simply put, static pressure is the resistance experienced by air as it passes through your system. High static pressure means there’s a lot of resistance. This can inhibit airflow throughout your home and tax your heating & cooling units.
On our side, things get a little bit more technical. There are acceptable levels of static pressure for a system. These acceptable levels can change from system to system, and can also change depending on where you’re measuring the static pressure.
All major HVAC equipment comes with these ranges for acceptable static pressure, and a good installation will make sure the system is operating within them.
What Is a Static Pressure Drop?
Static pressure drop is the drop in air pressure between two points in an HVAC system.
Remember when I said acceptable static pressure levels can change depending on where it’s being measured? Imagine measuring air pressure on either side of a filter. It’s going to change because it no longer has the filter slowing down airflow.
Some amount of pressure drop is expected and accounted for in furnace construction. Your air can’t go unfiltered, or you’ll have bigger problems. But not all filters are created equally, and some have higher pressure drops than others.
The Aprilaire filters I mentioned earlier are among our favorites for this reason. Not only do they have higher MERV and CADR ratings than entry-level filters, the static pressure drop is often lower as well because they’re designed to promote airflow.
How Do Filters Contribute to Static Pressure?
A clogged filter will block air. This, in turn, will increase the static pressure in the system immensely. As a result, your blower fan will have to work extra hard to move air throughout your ductwork and home. This can create numerous problems, both short-term and long-term.
Importantly, the cheaper one-inch filters are often so dense that they prevent air from flowing freely. Their static pressure drop is often quite high, and makes it advantageous to get a better filter.
What Are Some Problems Caused By High Static Pressure?
Your whole system is affected by anything that affects airflow. Therefore, a lot can occur when your static pressure is off:
- Hot and cold spots can form in your home where the air isn’t reaching them.
- Your system can become noisier because it has to work harder.
- A clogged filter or dirty areas of your furnace will increase static pressure, but also increase the amount of dust, dirt, and grime in your ductwork and home.
- Your furnace or entire system can break down as a result of the additional pressure put on it.
So is this important? Heck yes it is! In fact, we’ve “repaired” systems where the only thing wrong with it was a hopelessly clogged filter. Don’t let any of these happen to you by neglecting your filters.
And to cover our bases, low static pressure can be an issue as well, but this generally occurs for reasons outside your filter such as ductwork that’s too large for your home.
Clean Your Air, Improve Your Life
So how do you choose the best filter for you, your home, and your family? Ask the right questions.
Do you have pets? How many? Allergies? Health concerns? Would you rather pay a lot upfront and not have to replace your filter, or pay less and schedule regular replacements?
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These questions and more can help you decide. If you’re ready to assess your options, a good place to start is by contacting your trusted HVAC partner and scheduling a free estimate. Often, filters are included with a new system installation, but provided you match the right size filter to your system, you can install a new filter type at any time.
If you’re ready for that conversation, we’ll be happy to walk you through your options to help you make the best decision for your home!
