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HVAC Air Filter Buying Guide

April 11, 2024

How to Select the Best Furnace Filter


At APES we believe that selecting an air filter is what separates you and your sensitive central forced air equipment from the destructive particles in your home’s air. We want you to preserve your AC unit as long as possible but you can’t just pick any furnace filter off the shelf. In order to effectively protect your system, (whether it’s a furnace or air handler) while improving indoor air quality, a filter needs to be properly sized, installed, and rated. Here’s some easy ways how.

STEP 1: Measure Your Furnace Filter

First, locate the filter slot in your furnace/air handler. Some homes have filters behind their return vents as well. Furnace filter size is measured using length, width, and depth. For example, a furnace filter that measures 18”x16”x1” is 18 inches long, 16 inches wide, and 1-inch deep. You can make these measurements with a simple tape measure. The easiest way, though, is to simply look at the filter already in there and buy the same size.

STEP 2: Choose Your MERV Rating

The Minimum Efficiency Reporting Value (MERV) measures how effective a furnace air filter is at capturing particles.Furnace filter Merv ratings use a scale of 1-20. The lower the MERV number, the less effective the filter is at capturing particles (measured in microns) from the air. As the value increases, the filter captures smaller and smaller particles at a higher rate but also restricts airflow. If you or a loved one suffer from allergies or asthma, it may be more beneficial for you and your family to invest in a whole home air purifier and go with the lower rated filters. This will keep from decreasing the air flow but will purify the air for the whole home.
If energy efficiency is a higher priority for you, then a lower-MERV filter will work, as it will prevent the largest particles from entering your system without reducing airflow. Just know that, although you will pay less up front, you will need to replace it more often.

STEP 3: Choose Your Filter Type

Choosing your MERV rating will narrow down your filter media options. There are two throw away types which can be purchased at Home Depot, Lowes, WalMart and most local grocery stores. Fiberglass and Pleated, both filter the air in your home just in different ways.

IMPORTANT: If your system is not designed to compensate for the reduced airflow of, say a MERV 12 or 13, then you can end up freezing the evaporator coil or even crack your heat exchanger. In that case, you would need to purchase an additional indoor air quality system. HEPA filters have the highest MERV ratings and are used in hospitals and medical facilities. Most residential HVAC systems are not designed to accommodate the extremely restricted airflow from HEPA filters.


STEP 4: Replace Your Filter Regularly

Unfortunately, you can’t just install your filter and forget about it. Eventually, it will clog up from all the dust and particulates, reduce airflow to the furnace, and become ineffective. How often you must replace your filter will depend on the type you purchased and your home’s air quality. On average an air filter will last between 30 & 90 days, depending on the environment in the home. Homes with heavy carpeting, pets, kids, and a lot of foot traffic (doors opening a lot) will require more filter changes than those with one or two people and no pets. The best way to judge is to replace the filter and check it once a month. If you use a white or green filter the dirt will show up and be more visible. This will give you the time frame for when the filter needs to be changed.


*** The change days listed on the packaging is just a guideline and should not be taken as a definite for any home.

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