Club Benefits
If your energy bills are starting to rise as the weather drops, there’s an easy way to save money right away. When your HVAC filter is dirty, your system has to work harder and uses more energy. Try a quick “light test” to check your filter. You might save $10 to $20 on your bill this month, depending on how much you use your system and your rates. It only takes two minutes, and you don’t need any tools.
“A dirty filter makes your system work harder, using more energy and unnecessarily driving up your utility bill,” says Jason Kerr, president at Intelligent Service.
Ben Hubbert at Wright Home Services explains it simply: “A clogged filter makes your AC work longer and harder for the same result, which means you’re paying more and getting less”.
What happens if you never change your AC filter?
When filters get clogged, airflow is blocked. This makes the blower motor run longer and use more electricity. But wasted energy is just one issue. In cooling mode, low airflow can freeze the evaporator coil and even damage the compressor. In heating mode, furnaces can overheat and trip safety switches, and heat pumps can build up high pressure and shut off.
Chris Hunter at ServiceTitan says that if a system overheats again and again, it can crack the heat exchanger. In gas systems, this can pose a carbon monoxide risk.
This is a year‑round issue because the same filter and blower serve both heating and cooling. As Hubbert notes, you end up paying more for less comfort while putting extra wear and tear on expensive parts.
How often should you check it?
Check your filters every month. Basic fiberglass filters should be replaced about every 30 days. Pleated filters with a MERV rating of 8 to 11 usually last 60 to 90 days. However, if you have pets, allergies, smoke, construction dust, or use your system heavily, you should change them more often, according to Kerr.
Hubbert also recommends checking filters monthly. He warns that filters with higher MERV ratings trap more particles but can clog faster. If the filter does not match your system, it can add resistance and make your AC work harder.
Matt Gorbacz, air-quality specialist at Clean Air Technologies, suggests checking high-MERV 12-16 filters every 30-60 days.
Check your filter in just two minutes: the light test
Before you start:
- Switch off the system at the thermostat to make sure the blower stops running.
- Look for the filter. You’ll usually find it behind a return grille in a hallway ceiling or wall, or in a slot at the furnace or air handler. Some homes have more than one return, so you might have several filters.
1. Remove the filter
Open the return grille or slide the filter out of the unit. Look for the airflow arrow on the frame and check the size printed on the edge. This will help when you need to reinstall or replace the filter, says Hubbert.
2. Do the light test
Hold the filter up to a bright window or use a flashlight to shine light through it.
If you can barely see any light coming through, it's time to replace the filter. If light shines through evenly, the filter should still work.
3. Reinstall or replace
Put the filter back in with the airflow arrow facing the blower. If it doesn’t slide in easily, it's likely the wrong size. Mark today’s date on the frame.
Does the light test have expert approval?
Use this mainly as a quick gut check, not a precise test. “The two‑minute light test is a good go or no‑go check,” says Kerr, “but it's not foolproof. High‑MERV filters naturally block more light, even when clean.” If your filter looks gray, feels dusty, or your system is running longer than normal, it's time to replace it.
Essig also sees it as a rough indicator. For a more objective approach, he suggests checking your filter on a schedule or using a simple differential pressure gauge.
Some professionals do not recommend this method. “Different filters are made of various materials, and dust that clogs airflow is not always visible,” says Scott Levene of Levco. He suggests relying on the filter’s condition and a regular schedule, not just the light test.
Randy Huckstadt, an HVAC expert from JustAnswer, is “not a big fan” of the test either, but he agrees it can quickly show when a filter is clearly dirty.
Common mistakes that cost you
- If the filter is the wrong size or doesn’t fit well, unfiltered air can slip past, making the coil and blower dirty more quickly.
- Be sure to install the filter in the right direction. If you put it in backward, it can lower efficiency and put extra strain on the blower.
- Using a filter with an MERV rating that is too high can be a problem. Most homes do well with MERV 8-11 filters. Very high MERV filters are okay if your system is designed for them, but they can make airflow more difficult and increase pressure. Huckstadt says most residential systems should avoid MERV 11 or higher unless the system calls for it.
- Don’t put washable filters back in while they’re still damp. Let them dry completely to prevent mold and extra resistance, says Levene.
The simple payoff
Keeping your filter clean helps air flow better, makes your system run less, and protects your equipment. Technicians say dirty filters can waste five to 20 percent more energy, costing you $10 to $30 or more in a busy month. Locker calls this “one small, easily fixable issue that can save you $8 to $30 on a winter heating bill,” and it helps during other seasons too.
Set a reminder each month to check your filter. Hold it up to the light to see if it’s dirty, and replace it as needed. This way, you won’t end up paying extra for a clogged filter all season.
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