Furnace Filters: Everything You Need to Know

Selecting the right furnace filter for your heating and cooling system is crucial when it comes to producing and sustaining a healthy, clean and pure home environment. For those who don’t know, or just need a reminder, furnace filters remove dust, dirt, pollen, allergens, bacteria and other air pollutants from your home’s air – enhancing indoor air quality for you and your family. Just selecting the correct filter is not enough to guarantee safe air. You must also make sure you are following the guidelines and conditions based on your manufacture’s manual. This will ensure your system runs efficiently and effectively.

person replacing air conditioner or furnace filter
Serenethos / Shutterstock

Factors to consider before buying a furnace filter

Below are the most important factors to consider when selecting an air filter for your home:

  • Filter size: The most typical sizes for a furnace filter are 16″ x 20″, 20″ x 25″ and 16″ x 25″ however many other sizes are available for purchase on our site. The size of your filter will be located on the side of the door on your filter cabinet. The filter must fit snuggly in your furnace.It is important to note that you must have an exact fit for your cabinet -“close enough is not good enough” in these circumstances. A good fit prevents air from slipping around the edges of the filter.Another important note is that many manufacturers produce filters that are compatible in other companies cabinets.
  • Filter thickness: A filter’s thickness can range from 1″ to 5″. As a general rule of thumb, a thicker furnace filter will last longer and can be more efficient.Your system configuration will determine the thickness of the filter that you can use.
  • Pleated vs. non-pleated: For the most part, pleated furnace filters are more efficient and last longer than simple fiberglass non-pleated filters. Pleated filters contain much more surface area to catch pollutants/contaminants and have the ability to have smaller pores to capture smaller particles while still allowing full air flow.
  • Filter efficiency: Use MERV! MERV is the standard rating system accepted by The American Society of Heating Refrigeration and Air Conditioning Engineers (ASHRAE) and the air filter industry.This numbering system captivates a system enabling consumers to evaluate and compare mechanical air filters for overall effectiveness in removing airborne particulates. In the most simplified explanation, the higher the MERV rating, the greater the efficiency in removing contaminants and pollutants. Merv 10 is typical for a normal household. However, if anyone in your home has allergies, asthma or any other respiratory conditions, pets or if you live in a dusty environment you should aim for a MERV 12 or higher rating.

Want to get a system check-up just to be safe?

Furnace filter replacement

Regular replacement of your heating, ventilation, and air conditioning (HVAC) unit’s filter is an essential part of maintenance. As a homeowner, you will want to make sure your unit runs as efficiently as possible in order to minimize your electricity costs, ensure proper functioning of your unit and increase your unit’s lifespan. The filter is responsible for removing contaminants from your home’s indoor air before you breathe it in as well as maintaining the cleanliness of your HVAC system’s ductwork.

How often should you replace your furnace filter?

The average home and HVAC system will need the filter replaced once every three months. The type of filter you use will impact how often it needs to be changed, as will your home size, how often your HVAC system is on, if you have pets in your home and if anyone in your household has allergies or other medical conditions.It’s good practice to check your filter every month, especially if you have just installed a new system. Paying attention to changes in your home (such a construction) and in your city (construction nearby or large amount of pollution) will also help you decide when to replace the filter. If you notice the furnace filter’s surface is gray and covered in buildup, you should go ahead and change it. Other signs you may need to change your filter are more dust in the home or longer heating and cooling cycles.

Furnace replacement FAQs

Where’s the filter on my furnace?

Your furnace filter is usually located between the return air duct and the furnace or air handler. Look for the grill opening that draws air into it; this is your return duct, and the furnace filter will be somewhere nearby. If you still can’t find it, check your furnace’s manufacturer website for specifics on your unit. 

Do all gas furnaces have filters?

All furnaces, even gas furnaces, have filters. Filters maintain the furnace itself as well as the air quality in your house, therefore your unit needs a filter. 

How does a dirty filter affect a furnace?

There are many hazards that are caused by not replacing your air filter on a schedule. A dirty filter can cause your air conditioner to stop cooling, reduce efficiency, or cause your air conditioner to freeze up. Then, when it thaws the water from the melting ice can overwhelm your condensate drain and cause water damage.

Dirty filters can also cause mechanical issues with your compressor in your air conditioner or heat pump and ultimately cause your furnace and/or heat to stop heating. All of this can result in hundreds of dollars in repairs, not to mention the impact dirty filters can have on your health. Most filters cost between $20-$80 so it is worth the time, effort and money to regularly replace your air filter rather than pay for the cost of repairs due to a dirty one.