4-Inch Air Filters: Are They Really Better?

When it comes to improving air quality, is a 4-inch air filter really better than a 1-inch filter? The answer is yes, but it depends on the type of filter and the size of your HVAC system. 4-inch filters offer a higher range of MERV ratings, with a slight overlap with 1-inch filters. With a 4-inch filter, you'll get at least an 8 MERV rating, and up to 16 MERV rating for supermicro contaminants such as bacteria, viruses and dust particles. A 4-media air filter also offers a longer service life than a 1-medium air filter due to its larger surface area for trapping airborne contaminants.

This means fewer filter changes, which translates to less money spent and more convenience. Thicker filters, known as media filters, are usually 4 to 5 inches thick compared to the ubiquitous 1-inch filters that can be purchased at grocery stores. However, the combination of a thin air filter with a high MERV rating can also restrict airflow to the point of impairing efficiency and causing excessive wear and tear. It is recommended to change media filters every two to four weeks, which may be difficult for some to maintain.

Check the filter every 1 or 2 months during heavy use and replace it when necessary to avoid the types of efficiency and mechanical problems discussed in the section on 1-inch oven filters. And while media filters produce more airflow (less pressure drop) and clog less easily, you should be careful with the MERV rating. One consequence of a very effective air filter is the speed with which it can be loaded with contaminants and begin to increase the pressure drop. Therefore, if it is absolutely necessary to install these thicker filters on a return grille, it is recommended that your return duct be completely sealed and airtight.

That said, the 1-inch filter may be too shallow, causing a loose fit that allows unfiltered air to enter the ductwork. It may be comforting to know that your expired filter isn't as bad as it could be, but it won't do anything else for you until you're replaced. For example, Second Nature's Essential filter is about 450% more effective at capturing particles than a cheap low-efficiency fiberglass filter, but its airflow resistance is only 20% higher, a marginal difference. However, older units may not have enough air pressure to force air through a higher efficiency filter. So if it fits your oven, then a 4-inch air filter is better than a 1-inch air filter when it comes to improving air quality.

It is important to remember that regardless of the thickness of the filter, home and business owners should regularly inspect their filter to ensure that it is not filled with contaminants.

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