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Greenleaf Heating & Cooling Blog

What’s the Worst a Dirty Air Filter Could Do?

changing-air-filterAh, yes… The air filter. An essential part of every forced-air heating and cooling system. This rectangular insert made of cardboard and mesh, whose sole purpose is just to get dirty and then be thrown out, can become a harbinger of doom. When taken for granted, the air filter can restrict airflow and cause your HVAC system to display several troubling symptoms just short of disaster. All because someone forgot to change it when it got too dirty!

But seriously speaking, air filters are perfectly safe and very necessary. Without them, your HVAC system’s sensitive components would become contaminated. But it’s true that if it isn’t changed regularly, it can cause some issues, such as:


Your HVAC system is designed to go through numerous heating/cooling cycles. The air comes on for several minutes, disperses air through the home, and then shuts off. It then repeats this cycle numerous times. However, if these cycles suddenly become sporadic and occur rapidly, the system might be short-cycling.

This is very stressful on the HVAC system’s components and it will prevent your home from reaching the desired temperature. In the best-case scenario, short-cycling is easily fixed by changing the air filter.


When an air filter clogs up a heater, it can have some terrible consequences.

Natural gas furnaces require plenty of oxygen to combust the natural gas into heated air. Without enough oxygen, the furnace might suck oxygen out of the surrounding air to compensate, and that can sometimes produce rolling flames. One way this might happen is if the furnace’s airflow is blocked by a dirty air filter.

There’s also the possibility that it can cause a heater to overheat. Furnaces will have a limit switch designed to shut off the furnace just enough to prevent overheating. If this switch is broken, however, it might shut the furnace off entirely or not work at all.

Frozen Coils

While an air conditioner is not going to overheat from a dirty air filter, it can actually do something like the opposite: freezing over.

The evaporator coils, housed in the indoor unit, are in place to absorb warm air. If the air flow is restricted, however, that can cause the coil to become too cold instead, eventually turning the coil into a big block of frost and ice. If gone on long enough without maintenance, it can cause irreparable damage to the compressor.

Energy Bill Spikes

Through all of these symptoms, before they turn into disasters or complete breakdowns, they’ll end up taking a toll on your energy bill. That’s because your heater or AC is being forced to operate harder or longer than usual during these times.

If you see a sudden spike in your energy bill, as well as noticing that your HVAC unit hasn’t been performing up to standards, it could be time to change the air filter. If that doesn’t help, then the next step is to call in for repairs from an HVAC company in Long Beach, CA.

If changing the air filter isn’t enough, contact Greenleaf Heating & Cooling! We’ll help you find the problem.

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