Why Does Furnace Filter Thickness Matter?

Like the length and width, thickness is an important part of furnace filter sizing and getting the right fit to optimize performance. Air filter thickness ranges in size from 1 to 5 inches in depth - some options are more common than others, and your furnace may dictate what thickness you can use. Not sure which option is right for you? Keep reading to find the right filter thickness for you.

Why Are Some Furnace Filters Thicker?

Furnaces come in various sizes and configurations, which means there isn’t a one-size-fits-all filter. Beyond fit, there are also two performance factors related to the thickness of a furnace filter. A deeper depth can improve the lifespan and efficiency of the filter as well - they also make it easier for air to move into and out of your filter.

Is a Thicker Air Filter Better?

Thick air filters may automatically seem like the better option. More thickness means more filtration, right? In most situations that is the case. Thicker air filters tend to last longer because they have more square footage to capture and hold air particles. To put it in perspective, a 1-inch air filter may need to be changed every month whereas a 4-inch air filter could last up to six months.

Some AC specialists have also noted that thicker filters are better at providing a tight fit that doesn’t allow unfiltered air through. At the same time, a thicker filter is less restrictive and will allow for better flow of purified air. A 4-5” filter is usually best for people that need superior filtration.

But there are situations when a thin air filter is better. Let’s look at a few examples.

4-Inch vs 1-Inch Furnace Filters

The 4-inch thick air filter has a definite advantage over the 1” filter in terms of longevity, airflow and maximum filtering potential. Thus, if it fits your furnace, then a 4-inch air filter is better than a 1-inch air filter in regards to improving air quality. At FilterBuy, the price difference between 1-inch and 4-inch air filters is often only a few dollars. Because a 4-inch filter lasts longer, it usually provides better value.

But what if the air filter compartment in your furnace is only 3” thick? In that instance, the 1-inch furnace filter is the better option versus the 4-inch filter, however, a 3-inch thick air filter is the best choice.

1-Inch vs 2-Inch Furnace Filter

Again, if only the thickness is a consideration, then the 2-inch furnace filter is the winner. However, these two aren’t drastically different in thickness.

How Thick Should My Air Filter Be?

The thickness of the air filter depends on your system configurations first and foremost. The general best practice is to use the thickest air filter you can for maximum efficiency. BUT, never try to force an air filter to fit into a space that it isn’t designed for.

If you try to use a 4-inch thick air filter for a system that’s made for a 1-inch thick filter the efficiency will actually be worse. Not to mention, components could get damaged in the process. On the other side, you can certain use a 1-inch thick filter in compartments that can accommodate a deeper filter. That said, the 1-inch filter may be too shallow, causing a loose fit that allows unfiltered air into the ductwork. Going down in thickness by an inch shouldn't be a big deal - for example, you should be able to use a 4-inch filter instead of a 5-inch filter.

If you are considering a thicker air filter in order to improve air quality it may be better to focus on the MERV rating. Higher MERV ratings work best when the filter is 4” thick or thicker because they trap extremely small particles, which means contaminants will build up quickly on the screen.

If your system only fits a 1-inch or 2-inch filter, a high MERV rating could be detrimental. A 1-inch filter with less surface space will get clogged fairly quickly and need to be replaced much sooner than a thicker filter. The combination of a thin air filter with high MERV rate can also restrict airflow to the point that it hinders efficiency and causes excessive wear.

Now that you know what thickness you need, you’re one step closer to find your perfect air filter size - click here to get started.