It’s safe to say that most homeowners don’t pay as much attention to their furnace and air conditioner as they should. Of course, to keep it working efficiently and minimize energy costs there are some simple things you can do, including changing / cleaning your furnace filter on a regular basis … during both the heating & cooling season.

To complicate matters, there are a tremendous number of different filters to choose from. Getting the wrong one could cause damage to your heating / cooling system or cause it to wear out prematurely. Yes, furnace filters can help improve your indoor air quality too but they are designed first and foremost to keep your furnace fan and its components clean.

Filter Ratings

While there are different rating systems in the marketplace for filters, the minimum efficiency reporting value (MERV) is the most common. Not surprisingly, the higher the MERV rating is the better the filter is at removing particulate from the air. But it’s more complicated than that.

While a lower MERV rated filter is less efficient in scrubbing the air clean, it lets more air to pass through it and making it easier for your furnace to operate. On the other hand, those filters with the higher MERV ratings allow less air flow and can cause your furnace to work harder and longer. Since those higher MERV rated filters trap more, they need to be checked more often (try monthly at first) and will likely need to be changed more frequently as they get covered with particulate faster and can clog, restricting air flow. To assist at improving air flow, the higher rated MERV filters are pleated which creates more surface area for air to flow … and to trap more particulate. So, the bottom line is you need to have the perfect mix of air flow and MERV rating for your needs and that of your furnace / air conditioner.

MERV	Common particulate trapped by filter
1–4	Pollen, dust mites, sanding dust, spray paint dust, textile / carpet fibers, cockroach debris
5–8	Mold, spores, dust mite debris, pet dander, hair spray, fabric protector, cement dust, pudding mix, powdered milk
9–12	Humidifier dust, lead dust, milled flour, auto emission particulates, Legionella, nebulizer droplets
13–16	Bacteria, droplet nuclei (sneeze), cooking oil, most tobacco smoke and insecticide dust, most face powder, most paint pigments
17–20	Virus, carbon dust, sea salt, smoke

NOTE: Check the manual for your furnace, or contact the manufacturer or a licensed heating contractor, to ascertain what size and maximum MERV rating your make / model of furnace can handle. If your furnace uses a custom sized filter, replacements will likely be more costly and harder to find.

Types of Filters

While there are a number of different types of filters on the market, here are a few of the more common filter types:

MERV 2-3		Disposable fiberglass panel – inexpensive filter made using spun fiberglass. It has a low MERV rating and traps only larger debris from clogging up your system and does little if anything to improve your indoor air quality.
MERV 5-8		Disposable pleated – this popular MERV rated filter is relatively inexpensive, made from polyester or cotton paper, can remove some small particles like mold, spores, mites and pet dander.
MERV 8-11		Disposable electrostatic – contains self-charging electrostatic cotton or paper fibers, is relatively inexpensive, typically has a higher MERV rating than its permanent version and is designed to attract & trap small particulate.
MERV 8-11		Permanent reusable electrostatic – similar to the disposable version but with a lower MERV typically, self-charging cotton fibers attract particulate, but has a removable washable filter that can be used for five years or so if cleaned / maintained properly at least every 90 days.
MERV 14-16		High-efficiency pleated box – these higher MERV filters are 4” to 5″ thick and made from pleated synthetic cotton. They are more costly than other disposable & non-permanent / washable filters, but designed to trap smaller particulate.

Cleaning / Replacing Furnace Filters

• Ensure you turn off the power supply to the furnace before changing / cleaning your filter.

• Vacuum inside the furnace cabinet by the filter opening and blower / fan as well as around the outside of the furnace before replacing the filter.

• Vacuum washable / reusable filters before washing them.

• Filters have an arrow on them indicating the direction of airflow. The arrow needs to face the furnace side towards the fan / blower compartment when replacing it to ensure its proper operation.

• Once you have your filter replaced turn the power supply to your furnace back on.

• Check your filter monthly

• Clean your reusable / washable filter every 90 days or as needed.

• Replace your disposable filter every 90 days or as needed.

NOTE: Do not clean or change your furnace filter unless you are completely familiar with your furnace and comfortable in doing so, otherwise contact a licensed heating contractor for assistance.