Furnace & AC Air Filters

A filter is called an “AC” or air conditioning filter if it’s used in a cooling or air conditioning application. An AC filter traps particles in the air before they enter the AC system. It catches dust, pollen, mold spores, and pet dander so they don't circulate through the house It also protects the air conditioning coil and other cooling components from a build-up of dirt, grime, and other airborne particles. AC filters can be made of various materials, from fiberglass mesh in a cardboard frame to pleated synthetic fabric in a beverage board frame. As air passes through the porous filter, larger particles get stuck in the fibers or folds. Clean air then flows into your AC unit and eventually into your home.

Furnace filters are the first defense against airborne dirt and dust particles that harm HVAC systems and contribute to dirty indoor air. The filter prevents the dust from building up in the heating components inside the furnace and circulating into the rooms. Filters are referred to as “furnace filters” when they are used in heating applications, but in most cases, they are the very same filters used in air conditioning applications.

Yes, they are usually the same. Most whole-house HVAC systems use the same system of ductwork for both heating and cooling applications, so the “AC Filter” and “Furnace Filter” are the same component.

AC Filters & Furnace Filters

Like any other HVAC filter, an AC filter stops airborne pollutants in their tracks. They trap the particles so they don't compromise the performance of the cooling coil and other expensive system components. The result is cleaner air and improved system performance.

Where Do I Place the Air Filter?

Look for a slot or cabinet in the air return duct, which you can typically find near the air handler.

How Does an AC Filter Function?

The primary function of the filter is to protect the air conditioning components in the air handler. It traps particles, such as debris, mites, dust, particles, bacteria, allergens, and contaminants as the air circulates through the house.

How Long Does an AC Filter Last?

It depends on whether you have a disposal or washable filter. If you have a disposable filter, you'll need to change it every one to three months, based on manufacturer specifications. A washable filter can last for several years with monthly cleaning.

What Is the Best MERV Rating for AC Filters?

You can purchase an AC filter with the right MERV (Minimum Efficiency Reporting Value) rating for your house. Most experts recommend a MERV rating of 4 to 13 for a proper balance of filtration and airflow.

Types of AC Filters

The best AC filters are pleated. They range from $10 to $60, depending on the size, material, MERV rating, and filter thickness.

Where Do I Place the Filter?

The furnace filter is the same as the AC filter and is installed in the same place. Look for a cabinet or slot on the return side of your air handler/blower assembly. Depending on the system, the filter may be installed in a return grille on the ceiling or wall (more information on this later in the article).

How Does a Furnace Filter Function?

Furnaces are notorious for dust and dirt buildup, which affect system performance. The filter drastically reduces particle buildup. It traps dust, contaminants, allergens, and, in some cases, harmful bacteria.

How Long Does a Furnace Filter Last?

The main thing you need to consider when considering furnace longevity is thickness, which translates into surface area. For instance, a 1" thick furnace requires replacement every three months. A 4-5" thick filter can last up to nine months or even an entire year.

What Is the Best MERV Rating for Furnace Filters?

Most homes require a filter with a MERV rating of 4-13. You want a filter that balances proper filtration with unrestricted airflow. Check with the furnace manufacturer to find out the best filtration options.

Types of Furnace Filters

When it comes to furnace filters, you have lots of options. Choose from fiberglass, polyester, pleated, carbon, and washable. Filters cost between $15 and $100, depending on the type of filter you buy.

The main thing you need to consider when considering furnace longevity is thickness, which translates into surface area. For instance, a 1" thick furnace requires replacement every three months. A 4-5" thick filter can last up to nine months or even an entire year.

A traditional HVAC system combines a central air conditioner and a furnace. Both heating and cooling systems distribute air through the same ductwork, which circulates the air through your home. Since both units share the same ductwork, they may also share the same air returns. If so, both the air conditioner and the furnace use shared filters. The same filter cleans the air regardless of which system you turn on. There are some benefits of using shared filters:

• Less hassle when shopping for filters
• More bundle options, more savings
• No more searching for different sizes
• Consistent replacement schedule
• Replaceable and washable options are available

Americans now spend around 90% of their time indoors, where air can be 2-5 times more polluted than outdoor air, according to the EPA. Air filters are the primary component that helps you maintain a cleaner environment in your home. For this reason, they are a core part of AC and furnace maintenance. Here are five practical benefits of changing filters according to manufacturer specifications:

1. Improve the Air Quality in Your Home

An air filter traps dust, pollen, pet dander, mold spores, and other airborne particles, resulting in cleaner air. Changing the filter allows it to trap particles more effectively.

2. Get Higher Efficiency from Your System According to the Department of Energy, regularly changing your air filter can save you 5-15% of energy consumption and utility bills. Preventing dirt buildup allows the air to flow more smoothly so that the unit doesn't have to work harder than necessary.

3. Extend the Life of Your System Most air conditioners and furnaces last ten to 15 years. However, you must provide ongoing maintenance if you expect them to last that long. Doing something as simple as changing the filter reduces wear and helps the moving parts last longer. It can also prevent you from voiding your warranty if you have a problem with your AC or furnace.

4. You Pay for Fewer Repairs A furnace or air conditioner needs repair mainly because it has moving parts. These include a blower motor, compressor, evaporator coil, condenser fan, and heat exchanger. Dust and dirt buildup make it difficult for the parts to move. Eventually, they need repair. A filter can reduce buildup, allowing the parts to last longer with fewer repairs.

5. You Achieve More Temperature Control When the air is cleaner, the HVAC can regulate airflow. As a result, you can maintain the desired temperature more consistently. You get balanced airflow coming through every vent in the house. Plus, you get more accurate readings on your thermostat.

Both HVAC manufacturers and technicians replace the filters every 90 days. If you change the filter sooner than that, you may waste money. If you change it later, you get a dirty system. You must consult the furnace or AC owner manual, as each system has specified requirements. If you opt for washable air filters, you only need to change them once every five years. The tradeoff is that you need to clean the filter. How often?. At least once a month. Again, check with the HVAC or filter manufacturer for the best replacement schedule for HVAC efficiency.

You may notice grated vents called return air grills on your walls or ceilings. They're a part of your HVAC system.

An air grill filter allows air from your rooms to flow back into your home's HVAC system to be heated or cooled again. Some return air grills have a filter slot where you can insert a filter. The filter catches dust, pet hair, and other particles before the air re-enters the HVAC system. Regularly replacing these filters is important because clogged filters make your HVAC system work harder, wasting energy and money. They also prevent dirt and dust from building up inside your HVAC equipment.

You will normally use one or the other - but not both. Return air grille filters are typically used in parts of the country where the HVAC equipment is not easily accessible - like an attic or crawlspace.

When HVAC technology changes, new filters are required to accommodate the latest models; as a homeowner, you will benefit from a wide range of advanced filters designed to work with your system. Here are some of the most popular air filters available today.

HEPA Filters HEPA (High-Efficiency Particulate Air) filters are made of dense mats of fine fiberglass fibers. They can remove at least 99.97% of airborne particles as small as 0.3 microns. HEPA filters have very high MERV ratings, typically between 17 and 20.

HEPA filters are commonly used in hospitals, cleanrooms, and homes of people with severe allergies or respiratory issues. However, if not properly sized for the HVAC system, they can significantly restrict airflow. Therefore, they are almost never used in residential HVAC applications.

Electrostatic Filters

Electrostatic filters use static electricity to attract and capture particles from the airstream. They don't restrict airflow as much as other high-MERV filters. The average MERV rating for electrostatic filters is around 10-16. Some electrostatic filters are washable and can be reused for long periods of time. When properly maintained, they can effectively remove pollen, dust, smoke, and smog particles.

Carbon Filters

Carbon filters contain activated carbon or charcoal that helps remove odors, gases, and larger airborne particles. They have relatively low MERV ratings, around 4-8. Carbon filters are often combined with particle filters to improve indoor air quality. Their main purpose is absorbing volatile organic compounds (VOCs), smoke odors, and other gaseous pollutants rather than particulate matter.

Pleated Air Filters

Compared to flat panel fiberglass or polyester filters, pleated filters increase the surface area available for particle capture. They also allow higher MERV ratings for residential use, typically between 7 and 13. The pleated design also reduces airflow resistance. Pleated filters can remove pollen, dust mites, mold spores, lint, and pet dander. Higher MERV pleated filters may require more frequent changing to avoid excessive pressure drop.

Regarding filter maintenance, you have two main choices for AC and furnace filters: replaceable and washable. Both types of filters offer pros and cons. For instance, you don’t have to clean replaceable filters. Conversely, you don’t have to keep buying washable filters. Let’s look at best practices for maintaining each type of filter and the impact of maintenance on HVAC system longevity.

What Are the Best Practices for Filter Maintenance?

Disposable Filters As a rule, you want to replace most air filters every 90 days. For most filters, the three-month mark is when the filter has reached capacity for filtering out particles while not restricting airflow. Ninety days is typically the standard for pleated filters. Fiberglass and polyester panel filters should be replaced monthly.

Washable Filters Clean the filters every month, depending on your home environment and the type of filter you have. If you have pets or allergies or live in a dusty area, you’ll want to clean the filters more often. Follow the manufacturer's instructions for cleaning the filter.

Air Conditioner Filter Replacement: 5 Signs That Your Current Air Filter Needs Replacing

If your AC or furnace isn't cooling/heating as effectively as before or the airflow weakens, a clogged filter could restrict proper operation. A dirty filter forces the HVAC system to work harder, leading to higher energy bills without changing thermostat settings. Here are some common signs that you need to replace or clean the filter:

• It’s a dirty air filter with visible dust and dirt buildup on the filter
• Poor system performance
• Increased energy consumption
• Unusual noises from the HVAC unit
• Musty or unpleasant odors

Strange sounds like humming or rattling can indicate strain on the system from a blocked air filter. Dirty filters can accumulate damp debris, bacteria, and contaminants that produce stale, musty smells when the system runs.