A furnace filter is an essential part of your HVAC system. Yet, we tend to ignore its working and eventually that leads to a malfunctioning sooner or later. Apart from the fact that a furnace filter is required to keep your home warm in winter and cold in summer, there are some other aspects that you need to pay attention to. Here we share with you all that you need to know about furnace filters.

The working of a furnace

A traditional furnace draws air through return ducts and warms it using a heat exchanger and then transports the air outside so as to warm a room in which it is installed. There is a blower fan that assists the furnace in doing so. Once the temperature of the room reaches the level of the setting of the furnace it would most likely shut off on its own.

Purpose of a furnace filter

Furnace filters must stop any dirt, hair or other gunk from damaging the blower fan of your furnace. While it is supposed to clean the air by stopping the contaminants from getting circulated outside, its main purpose is not that. Furnace filter only stops your return duct from piling dirt on to your blower fan. Any other benefit over and above that is just an additional advantage.

Rating of furnace filters

The minimum efficiency reporting value of a furnace decides how efficient it is. Higher the rating for any furnace filters the better it would be in keeping the particles away. However, such filters also allow less air to pass through and that may lead to your furnace malfunctioning after all. On average for any household, a furnace with an 8-11 rating is the most suitable. Some of the home improvement stores also have a separate rating system of their own. If you are planning to buy it, you may have to ask them how their rating system works.

Types of furnace filter

Disposable pleated filters are the most common variety of furnace filters these days. You would find them in different sizes and ratings and can choose one according to your home preferences. These pleated filters are made of polyester and paper and are efficient at controlling particles and allergens found in the home. The price of such filters ranges up to $40 and they need to be checked frequently and replaced every 90 days if required.

Another type of filter is the disposable fiberglass filters, and are rather cheap and have an appearance like a spider’s web. They are also available in many sizes but are usually flimsy and available in lower ratings.

Permanent reusable filters or washable filters have aluminum or plastic frame and are much more reliable than others. You can easily vacuum or clean them with water. If you check them frequently, they can last you for up to 5 years. However, this also means that they are expensive in comparison to other disposable varieties.

Electrostatic filters

Disposable as well as reusable filters have their electrostatic versions as well. This variety charges on its own even as the air passes through them. The process helps in controlling even the smallest of particles thus making it a worthwhile purchase for homes with pets or where there are active smokers. However, you may need to check your furnace manual to see if an electrostatic filter can be used there.

Size of a furnace filter

Normal furnace filters are assessed by the depth, height, and length. The common thickness used is 1” however in some filters 4” is also prominent. The height and length combinations may range from anywhere between 10” X 10” to 30” X 30”. In case you are in doubt about the size of the filter that your furnace uses, you may have to check the old filter or consult your furnace manual.

Replacing the filter

Once you know that your furnace filter replacement is due, it is the time to start working on the same. You may have by now figured out the size, MERV rating and filter type that you require. Make sure that you shut down your furnace while doing the replacement else it may show signs of malfunctioning.

First, you would have to open the filter door that would be located between the air intake and the furnace. Slide the old filter and quickly put it in a garbage bag. Normally the filter would be quite dirty and it is better to immediately dispose it off. If your filter is a permanent one, you must vacuum it and later wash it with water. Make sure that it has completely dried off before you start placing it in the furnace.

In case it has been a long time since you cleaned the filter, it is quite possible that the dirt has shifted to other parts of the furnace. Whichever filter you may be using there would be an arrow that shows the direction of the airflow. This arrow should be facing the furnace when you place your filter inside. If you want your filter to work properly, you must keep this fact in mind. Once the filter has been replaced put your furnace on to see if it is working as per your expectations or not.


The furnace filter is an integral part of your furnace and holds the key to the smooth functioning of the same. As and when you notice problems in its working, you must replace it. The above guidelines show the ideal procedure for deciding which filter to buy and replace it. You may buy your furnace filter from a reputed website online; just make sure that you have full knowledge of your furnace’s requirements.

Most of the websites offer these filters in various sizes and price points and you should go through the furnace manual to know which one is most suitable. Do check the reputation of the website before you plan on buying a filter as any wrong purchase may lead to you feeling fleeced later.