Types of Air Filters for HVAC Ductwork

Installing an air filter in your HVAC ductwork is the best way to achieve clean, breathable air for your entire home. A tight building envelope insulates a modern home well, improving temperature control. However, it contributes to more concentrated indoor pollution. The good news is various options can compensate for this; we’ll explore a few if you’re looking for an air filter replacement or upgrade.

Residential HVAC filters are available as media filters, which provide a physical barrier to trap particles. Meanwhile, electronic filters capture various particles and contaminants via a high-voltage electric charge. Some filtration solutions combine both methods to improve their effectiveness. 

What Is a Whole-House Filter?

A whole-house filter differs from the air filter installed in your furnace or air handler unit. It is typically placed in a return-air duct. From here, it traps particles before they enter the return airflow of a forced-air heating or central AC system. Unlike traditional AC filters, a whole-house air filter must be installed professionally. 

Best Types of Ductwork Filters

A built-in filtration system can serve as a whole-house purifier. As long as your HVAC fan is on, it constantly filters the air that passes through. The effectiveness and longevity of a filter depends on the type. These are the most common air filters for HVAC ductwork in homes:

Flat Filters

Matted fiberglass filters are often found in forced-air furnaces. They’re designed to capture large dust particles before they enter ductwork and other crucial components. However, the smallest microscopic particulates can pass through. These are major culprits of respiratory irritation, so depending on your home and whether you have allergies, asthma, or other issues, these filters aren’t always the most effective.

Fiberglass filters are good at keeping large particles out of sensitive HVAC components. However, they typically don’t have a Minimum Efficiency Reporting Value (MERV) of over 4. This means their overall particle filtration ability is relatively low.

Extended Media Filters

An extended media filter is a stacked set of filtration materials. The filtration media is set in an 8-inch-thick accordion-like pile. While pleated filters with cotton or polyester folds are a step up from fiberglass filters and have MERV ratings of 5 to 8, extended media filters can have a greater range of filtration power. 

But these filters aren’t for a DIYer. They require a professional to install in line with your ductwork within a specialized filter holder. The initial installation can cost $400 to $600, according to This Old House. However, the filter needs replacement only once a year, which generally costs $60 or less.

Electrostatic Filters

An electrostatic precipitator is a hi-tech option that also integrates into ductwork. It creates static electricity, which most people prefer to avoid. Instead of making your hair frizzy and causing annoying shocks, the high-voltage current helps trap particles, which take on an electric charge so a collector plate can attract them like a magnet.

Electrostatic precipitators effectively catch extremely small particles, like smoke particles and most allergens. Another advantage is they never have to be replaced, although the aluminum collector plates must be cleaned every few months. The plates can be cleaned off by rinsing them in soap and water. 

An electrostatic filter often includes a flat or pleated carbon filter to improve efficiency. 

Electronic Filters

Instead of static electricity, electronic filters produce a high-voltage charge generated by a transformer. An electronic filter is a mechanical air filter that plugs into an outlet. It won’t work if your HVAC system has a return grille filter. Nonetheless, MERV ratings of 8 to 16 mean they’re highly effective at filtering small particles. The higher upfront price tag is offset by the need for duct filter replacement only about once a year.

Electronic filters are generally safe and effective. However, when shopping around, look for third-party testing data on any product you consider. The filter should use an ionizer process similar to a whole-home air purification system and not generate ozone, which can be a health hazard.

HEPA Filters

High-efficiency particulate air (HEPA) filters come in many forms. Some fit inside air handlers, while others are designed for ductwork. They remove 99.97% of airborne contaminants. These include tiny dust, pollen, and smoke particles as well as pet dander, mold spores, and bacteria. Whether you suffer from allergies, asthma, or other respiratory issues, a HEPA filter can eliminate the tiny particles that trigger your symptoms.

Ultraviolet (UV) Filters

A built-in UV filter uses ultraviolet light to kill microorganisms, including bacteria and viruses. Short-wave UV light effectively neutralizes organic contaminants in the airflow. However, a UV filter does not remove dust and other particulate-based pollutants. Therefore, UV and HEPA filters are often combined into the same unit. Research your options before choosing one, as some filtration systems produce ozone from oxygen molecules.

Gas-Phase Filters

Less commonly used in homes, gas-phase filters use gas sorption to attract gas molecules to a solid surface. They effectively remove odors and volatile organic compounds (VOCs). An activated carbon and charcoal media is used but a short lifespan means the filter must be replaced frequently. Also, it only removes gaseous pollutants and is ineffective against other particulates; therefore, gas-phase filters are typically used as an add-on filtration option.


Why Do MERV Ratings Matter?

Every air filter has a MERV rating, which ranges from 1 to 16 and measures a filter’s ability to capture particles. The higher a filter’s rating, the more effectively it traps particles and the more expensive it is. 

Higher-rated filters can also reduce airflow and reduce an HVAC system’s efficiency. Therefore, filters with MERV ratings of 8 to 13 are recommended for homes. Your HVAC contractor can help find the best option for your system.

Where Are Air Duct Filters Located?

A standard HVAC filter fits in a slot above, below, or on the side of the air handling unit. Ductwork filters are placed in a return air grille in a wall or ceiling, just inside the vent. Or, they can be installed somewhere between the return duct and the air handler.

How Many Filters Does My Ductwork Need?

A small HVAC system may require just one filter. If you have a two-story home, it probably has two air filters (one for the upstairs HVAC system and one for the downstairs system). An additional filter may be needed for an indoor air quality solution like a whole-home mechanical ventilation system. An add-on ductwork filter provides additional filtration, so your heating and cooling system may have multiple filters.

How Do I Pick the Best HVAC Filter?

A pleated filter at least 3 inches thick with a high MERV rating is often considered an ideal solution. However, various factors help determine the best HVAC filter for your home. Some of these considerations include:

  • Airflow: Higher-efficiency filters come with the downside of increased airflow resistance. An HVAC contractor can help find the best filter based on your system’s specifications.
  • System Usage: A ductwork or whole-home air filter works only when the system is running. If you don’t need heating or cooling, you can turn on the fan setting and the filter will clean the air that circulates.
  • Maintenance: If you’re looking for the lowest-cost filter, expect to change or wash it every few months. Maintenance is essential for good indoor air quality. By investing a little more, you can benefit from a media filter with fewer maintenance requirements.

Lastly, the filter’s size and design must fit your HVAC system. If not sized correctly, a filter can let air escape around its sides. This counteracts its benefits and allows contaminants in.

Contact Trio Heating & Air

We provide indoor air quality services, including whole-house air purifier installation, for homeowners in the The Greater San Francisco Bay Area area. From thorough inspections to high-quality workmanship, we have you covered. Our ductwork filters and air purification systems capture dust, dust mites, pet dander, VOCs, germs, smoke, mold spores, and odors. Check online for special offers to help you save. For a consultation and a ductwork filter replacement or upgrade by trained professionals, call (415) 223-1647 today.

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