What is a Furnace Filter?

Homeowners often have many questions regarding their HVAC system. One of those questions is – what is a furnace filter? This is an important question as furnace filters are a critical component of the home’s HVAC system. This piece is what protects the internal furnace components from dust, debris, hair, and other pollutants floating through the air. It not only keeps the furnace running efficiently but also helps improve air quality. 

Where is the Furnace Filter Located? 

There are a few different places where a furnace filter can be, so it’s easiest to locate the furnace first. Generally furnace locations are next to other equipment like water heater or washing machine, otherwise they can be in the:

  • Basement
  • Crawlspace
  • Attic
  • Special utility closet

Once you find the furnace, you’ll often find the filter in the metal compartment near the floor or side of the furnace door. Another filter location is where the return air duct meets the furnace unit. If the filter isn’t near or within the furnace, check the return air vents in the ceiling or wall. If there are multiple return vents, be sure to check all of them as some larger homes have more than one filter. 

Sometimes filters find a really good hiding place. So if you can’t find your filter, ask your local HVAC technician for assistance! We can help you locate the filter and demonstrate how to replace it if needed.

Is the Furnace Filter the Same as the AC Filter? 

Indeed, the furnace filter is the same as the AC filter. This is because all systems use the same blower and duct system. Which in turn, means both heating and cooling units move air through the same filter.

How Often Should You Change Your Furnace Filter? 

The typical answer is every 90 days (three months). However, each home is exposed to different conditions which affect the proper time for filter replacements. If the home has central air, then the furnace usually shares the air handler with the air conditioner. In order to keep harmful debris away from the furnace, you need to know what your filter is dealing with.

Which Way Does the Furnace Filter Arrow Go?

Another frequently asked question is which way does the furnace filter arrow go? Airflow is meant to travel through the filter from a specific direction. This is the reason why furnace filters have arrows on them to display the correct orientation. So when replacing a filter, the arrow should always be pointing towards the furnace compartment. If the filter location is in a return vent, the arrow should be pointing towards the ceiling or wall. 

Another way to tell if furnace filters are facing the right way, is the differences between the front and backside of the filter. The front side (facing towards you) has the pleated material. The backside (facing away from you) usually has a metal mesh or cardboard frame.  

What Happens if Furnace Filter is backwards?

The direction of the furnace filter is actually really important. As the filter is made to let airflow pass through from a specific direction, the air won’t flow properly if it’s backwards. The furnace will sense it’s not receiving enough airflow and work harder to pull in more air, stressing its components. Not only will it cause an increase in energy bills, but also lead to furnace repairs. The decreases in efficiency and increases in stress often lead to shortened lifespans and even system failures.

Can I Run My Furnace Without a Filter? 

There are a lot of “what if” scenarios relating to this question. The simple answer is no. The purpose of a filter is to protect the furnace. Airflow is constantly moving through the furnace, along with every pollutant. These pollutants can quickly build up on internal furnace components causing mechanical issues and part failure. Other problems of running a furnace without a filter include:

  • Poor indoor air quality: pollutants don’t just build up and stay in the furnace components, they’re also moving throughout the house and into your lungs
  • Ductwork issues: Without a filter, dust can settle within the ductwork. If the dust then mixes with moisture within the dark ducts, mold can quickly set in and spread.

Can a Dirty Furnace Filter Cause No Heat?

Can a dirty furnace filter cause no heat? Actually, yes it can. The lack of airflow can cause a variety of problems. The first problem is without proper airflow, the temperature inside the furnaces rises beyond normal. This causes the safety feature to activate and shut down the furnace in order to protect its components. Once it cools down, the furnace will repeat the process for a few cycles before needing a reset. The repetitiveness of heating up and shutting down causes stress and even system failure. Furthermore, depending on the part that breaks down, your family could have carbon monoxide exposure!

Can a Dirty Furnace Filter Cause Carbon Monoxide?

As mentioned in our other blog, fuel burning appliances like furnaces, create carbon monoxide naturally. When functioning properly, a furnace will draw in enough oxygen to burn the fuel cleanly and vent out harmful gasses. The heat is then transferred to the air as it flows through – this is the heat exchanger’s job. However, the heat exchanger won’t be able to transfer heat without airflow, causing cracks from overheating. Harmful gasses in the combustion process can then leak out of the heat exchanger and throughout the home. So can a dirty furnace filter cause carbon monoxide? If the problem is left unchecked, causing stress on other parts, yes it can lead to carbon monoxide leaks.

Why is My Furnace Filter Wet? 

While this doesn’t happen often, homeowners discover that their furnace filter is wet. While moisture is a natural byproduct of a functioning HVAC system, it shouldn’t affect furnace filters. There is a condensate line and drain which disposes of the water. However, if either the line or drain clogs up it will lead to moisture building up. A note about condensation water is that this particular water is warm. This can lead to rapid mold and mildew growth.

Why is My Furnace Filter Black? 

The most concerning question a homeowner can ask is “why is my furnace filter black?” This problem can actually come from a few different sources. The first possible source is the most dangerous: carbon monoxide. It’s recommended to check the carbon monoxide levels if you notice a black, sooty residue on the filter. Keep in mind that other things like fireplaces, gas stoves, and even candles create soot residue as well. 

Another reason why the filter is black is due to mold growth. Any accumulation of dust, dirt, and moisture within a dark place is a breeding ground for mold. Rainy seasons can also increase the chances of mold growth within places such as basements, crawl spaces, and ducts. This sort of black is typically wet and slimy rather than dry and powdery of soot. Try not to touch black mold as much as possible as it is harmful to your health.  

Final Thoughts From Your Local Experts in HVAC: Joplin, MO

Information on filters, furnace units, and HVAC in general can quickly become confusing. If you have more questions about your home’s HVAC system, please don’t hesitate to reach out to us! We are happy to help answer questions and clear out any confusion so you can be confident in your home. Additionally, as heating repair experts in Joplin, our team at Satterlee offers inspection and furnace repair services. We can inspect, clean, and repair any furnace issue, even if it’s because of a dirty filter!

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