Clogged Furnace Filter Symptoms - What You Need to Know

Does it seem like your furnace isn’t working as well as it used to? It could be the result of a clogged filter. Several problems can be caused by a dirty HVAC filter, so its critical to catch the issue before it creates more damage. Here’s what you need to know about clogged furnace filter symptoms and what causes them.

How a Furnace and Its Filters Work

First, let’s take a step back and look at how a furnace works to better understand why a clogged furnace filter needs to be addressed right away.

A furnace is part of many heating, ventilation and air conditioning (HVAC) systems. It’s the piece of equipment that circulates the air in a home and regulates the temperature with a heat exchanger so that it’s warmer and more comfortable inside. The furnace has fans that push the warmed air into the ductwork so that it can be distributed throughout the structure before circulating back to the furnace to start the process all over again.

Once the set temperature is reached the furnace will switch off until it’s needed again to warm things up.

a woman checking the gauge of the furnace

During this process of intaking, warming and circulating air, the air needs to be cleaned of dirt, allergens and pollutants. As air comes into the system through the blower compartment, it passes through the air filter so that debris is caught by the screen before circulating through the furnace and eventually the home. Not only does trapping those particles improve your indoor air quality, but it also protects your furnace fans from debris that might damage it.

Dirty AC Filter Symptoms to Watch for With Your Furnace

You can usually tell a dirty HVAC filter needs to be changed just by looking at it. The filter will be gray or black and bits of debris will be visible. But you may notice other changes that indicate the furnace is not operating properly.

Below are five common dirty air filter symptoms and what causes them.

a dirty furnace

Increased Energy Consumption

Have your energy bills gone up significantly in the last month or two, even though the furnace is being used less and less? Dirty air filters could be to blame. When furnace air filters are clogged, it causes the fans to work harder because air isn’t flowing as easily. The increased power needed to run the fans can translate into higher energy bills.

Furnace Damage

A dirty air filter can cause significant furnace damage to the point that the equipment fails altogether. At the very least, the damage created by a clogged furnace filter can shorten the lifespan of a furnace.

The heat exchanger is particularly susceptible to damage from dirty air filters. The clogged filters will reduce airflow through the furnace, and lack of fresh air is bad news for the heat exchanger. The fans or pressure switches can also get damaged preventing the furnace from turning on.

Poor Heating

Having a dirty air filter at home or the office can make things feel a lot less comfortable inside. The damage caused by dirty air filters can make it difficult to get the home or business warm and maintain the temperature. This is often the result of poor airflow through the filter that reduces the blower fan’s capability to circulate warm air.

Short On/Off Cycles

When there’s a dirty air filter in the furnace, it can cause excessive heat to build in a component called the heat exchanger. A furnace is designed to automatically shut off and stop generating heat if the heat exchanger’s temperature reaches a certain point. This will turn off the burners and cause everything to go cold. Once the furnace has cooled off it should automatically turn back on.

If poor air circulation from a dirty HVAC filter is causing the furnace to turn off and on frequently you may notice the short cycles.

Increased Indoor Air Pollution

Air filters that are clogged can’t effectively do their job. More dust, allergens, pollen and pollutants pass through and enter the air. It can have a significant impact on air quality, and people in the home with allergies or asthma may have increased symptoms.
Can that dirty air conditioner filter make you sick? Not directly, no - however, the pollution in the air can exacerbate conditions like allergies, asthma, and other respiratory conditions.

Read more: What Is Indoor Air Pollution

How To Prevent the Symptoms of a Dirty Furnace Filter

All of these problems above can be avoided by simply changing out your furnace air filters before they become clogged. All it takes is a few minutes to get the benefit of lower energy bills, better air quality and enhanced comfort.

If you see or experience any dirty filter symptoms, inspect the filter right away. If there is noticeable debris or build up, replace the furnace air filter ASAP.

The frequency of air filter changes depends on several factors. First and foremost, you should follow the furnace manufacturer’s recommendations. Most HVAC air filters last anywhere from 30 days to 6 months, depending on dimensions and MERV rating. Of course, the more your use the furnace the sooner you'll have to replace the dirty filter. If there are smokers or pets in the home change or clean the air filter more regularly.

a man changing new air filters

Once you know your size and frequency, you can set up a filter subscription order and receive new filters exactly when you need them.