Your air conditioner and heating system keeps you comfortable by managing temperature and humidity, as well as removing particles—irritants and allergens—from the air. In order to do that effectively, it needs a filter, changed on a regular basis, that has the right balance between filtration and air flow. Here are some tips to match the right filter to your system and indoor air quality.
Residential or Commercial Application
While there is some overlap between residential and commercial filter applications, some commercial environments may have more specific requirements, or even high filtration needs (like industrial, laboratory, or medical applications). Most home users have needs based more on comfort, indoor air quality, and the efficiency of the HVAC equipment.
The level of filtration your home (or office space) needs depends primarily on:
- Outdoor air quality
- Indoor air quality
- Allergies and sensitivities of the inhabitants
Outdoor air quality in some regions is consistently contaminated with particles and allergens, while other locations suffer seasonal fluctuations, or even temporary pollution (as we’ve experienced with this year’s wildfires). Filtration needs—based on what’s outside—may therefore change periodically, so keeping up with outdoor conditions beyond just temperature is important for indoor comfort and efficiency.
Indoors, important considerations are the presence of pets (hair, dander), smokers, candle usage, cooking habits, and even the number of residents (activity levels, dust, skin cells, opening of doors and windows).
Beyond the particles that accumulate just by living, those with allergies and other sensitivities may need to take extra care to filter out particles that will make the indoor environment less comfortable, or even uncomfortable.
Air Flow Needs
It’s tempting to choose high filtration just to keep any potential contaminant out of your indoor conditioned air. But your HVAC system needs to breathe to move air through the filter and into your house, so air flow must be considered. Too little filtration provides plenty of air flow, but moves most if not all of the particles straight through into your living or working space. Too much filtration can make your system work too hard, cost you more money to operate, and even cause your system to shut down (or worse, result in property damage or fire if safety features malfunction or are bypassed). You have to strike a good balance between filtration and air flow, and higher levels of filtration will require more frequent filter changes.
Size and Material
The filter aisle at your local home supply store can be daunting. So many sizes, types, and filtration numbers. The first thing is to know what size your HVAC needs. This should be in the documentation that came with the unit, or you can pull out the current filter to find the dimensions printed on it. The sizes are the width, length, and depth (or thickness). For example, a 16” x 20” x 1” filter is a thin, 1-inch deep residential filter, rectangular in shape (16 inches x 20 inches). There are a number of “standard” sizes, and most are affordable—even to change several times per year. Custom sizes can be more expensive and hard to find.
Most users are familiar with disposable types—from the super cheap fiberglass, to the common pleated, to electrostatically charged filters. There are also high-quality permanent types that tend to have higher efficiency. Initial costs are higher, but they last a long time if you’re willing to clean them regularly.
Filtering ability is ranked by MERV rating—minimum efficiency reporting value. The scale runs from 1-20, with most residential filters topping out at 12.
HVAC manufacturers tune airflow based on a MERV of 2, but most residential users will be more comfortable with filtration at a minimum of 4.
The cheapest disposable fiberglass filters only meet the minimum (or slightly better), around MERV 2 or 3, and are designed to protect the inner workings of your HVAC system, rather than your indoor air quality. Some washable filters aren’t much better, but the higher end permanent filters can rival the very common disposable pleated filters, which are available in a range, even reaching MERV 12 or better. Electrostatic filters are usually on the higher end of that scale as well.
Many homeowners will be comfortable with a filter ranking 4-8. Higher MERVs of 8-12 are better for those with significant allergies or residences with smokers or pets, but filters will need to be changed frequently.
Consult your AC expert for tips on when to change the filter based on your equipment and filtration level, and keep an eye on the system’s performance and your energy bills to get the most out of it at the best operating cost.