Can I Use a 4 Inch Furnace Filter Instead of 5?

Learn about using 4 inch furnace filters instead of 5 inches for improved air quality and energy savings.

Can I Use a 4 Inch Furnace Filter Instead of 5?

If you're looking to reduce the thickness of your air filter by one inch, you should be able to use a 4-inch filter instead of a 5-inch filter without any major issues. However, it's important to ensure that the filter rating allows for the proper airflow and filter level. If the 5-inch filter fits and has a similar density, it will allow the system to move air with less resistance. I would caution against increasing the filter density, as this could affect the efficiency of the unit.

I once repaired a fan where the owners thought that if one filter was good, two would be better, so they bought some expensive HEPA filters. This caused the fan motor to run very hot and burned the grease on the bearings in just a few years. I added an electrostatic element and returned to the standard filter. After that, the owners reported that their house had more uniform heating and that their oven worked less.

When it comes to improving air quality, it's best to focus on the MERV rating. 4-inch filters cover 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. Higher ratings of up to 16 can control supermicrocontaminants such as bacteria, viruses and dust particles.

A 4-inch filter will last longer and provide better air quality for your home than a 1-inch filter. If you have an oven in your house, you may need to replace your clogged filter every 2 to 6 months. The number of “unclogged” pores will be greater in a thicker filter than in a thinner one. A 1-inch pleated air filter has higher MERV ratings because it has more surface area to trap particles.

The purpose of an air filter is to prevent dust and other large particles from damaging the heating and cooling system. Filters with higher ratings than that can restrict airflow and damage HVAC equipment. These filters are sufficient to stop allergens, dust, mold, bacteria, dust mites and pet dander from passing through. A 5-inch filter offers better air quality, ample airflow, longer lifespan, cost-effectiveness and greater savings in energy costs. If you choose a 1-inch air filter with a high MERV rating, check it every month during the heating or air conditioning months and replace it when it's too dirty for light to enter or sooner.