Why Is My Furnace Filter Black?

December 15, 2016

Every component of your HVAC, including heating, ventilation, and air conditioning system in Southwest Ohio, is important to your home. But your furnace filter is where impurities and airborne allergens are filtered.

The filter circulates clean, comfortable air. It’s normal for furnace filters to turn color over time, but if your furnace filter is black, it’s a red flag.

What Does an Air Filter Do?

After several months of use, you may notice dust and debris starting to collect on the air filter for your furnace. This is normal, but if it turns completely black, there may be a problem. Here are the most common reasons a furnace filter may turn black:

  • Excessive dust and dirt: High amounts of dust, dirt, and debris may turn a filter black in rare cases, but this would mean the air filter is almost completely clogged. This can damage the furnace, so it’s important to eliminate dust as much as possible. An air purifier may be a good option.
  • Candle or fireplace soot: If you burn candles or have a fireplace, small amounts of soot will be produced and distributed throughout your home. This can stain the air filter and turn it black, but in most cases, this is harmless. Just be aware of the issue and replace the air filter before it causes furnace performance problems.
  • Carbon monoxide: If your furnace, water heater, stove, or any other fuel-burning appliance is not working properly, it may release carbon monoxide into the air anytime the combustion process isn’t properly completed. This gas is odorless, tasteless, and invisible, and it can lead to serious illness or death if you’re exposed for too long. While carbon monoxide is invisible, the soot produced during incomplete combustion can stain the furnace filter, indicating the gas is being produced.
  • Mold growth: If the furnace filter is too close to the evaporator or there’s moisture inside the filter cabinet, mold can form on the filter. While most mold is harmless or may only cause moderate irritation, some, like black mold, can pose a serious health threat.

If you have infants, elderly, chronically ill family members, or loved ones with allergies, clean indoor air quality is critical. Your HVAC system’s air filter makes that happen.

One of your HVAC air filter functions is to trap particulates and dirt that can clog your HVAC system. This lets your HVAC operate more efficiently. If your HVAC has to work harder to deliver the same amount of comfortable air, your energy bills will increase.

Reasons Your Furnace Filter May Turn Black

The most prevalent reason for a black furnace filter is built-up carbon monoxide. Carbon monoxide can escape from:

  • Attached garages
  • Boilers
  • Fireplaces
  • Fuel-burning water heaters
  • Furnaces
  • Gas-burning stoves
  • Lawn and garden equipment
  • Power tools
  • Smoke from tobacco products

If your furnace filter turns black quickly, you have a problem that needs to be repaired. Carbon monoxide is hazardous to you and everyone in the house, including four-legged family members. Contact your local HVAC professional to learn what’s causing this dangerous problem.

Mold is challenging in any home with high humidity, but black mold can grow on your furnace filter. It usually starts forming in a moist area such as an evaporator coil and spreads. You’ll need professional HVAC cleaning and mold removal.

Another reason your furnace filter blackens is soot. Everyone loves a burning fireplace! And some of us burn candles every day. If this is you, make a habit of dusting and changing your furnace filter more frequently.

Clogged air ducts can turn an HVAC filter black over time. Ductwork services in the Cincinnati area should be scheduled every three to four years or more frequently if you live in an area with heavy construction or have two or more furry family members.

Can a Black Filter Make Me Sick?

Any time your HVAC filters are dirty, you risk health problems. Carbon-black filters can cause heart problems by reducing pulmonary function. Other signs of black filter health problems are:

  • Chest pains
  • Central nervous system damage
  • Coughing
  • Fatigue
  • Headaches
  • Internal or mucosal irritation from inhaling
  • Phlegm
  • Skin irritation

Benefits of Furnace Maintenance

Professional HVAC maintenance is needed to keep your system clean and operating efficiently. Maintenance can add several years to this expensive unit’s life span, meaning it’s an investment that pays off. If there’s an area-wide event, our maintenance agreement customers have top priority.

HVAC Service & Repair in the Cincinnati Area

If your furnace is on its last leg, we’ll tell you how long it may be safe to operate. We’ll do our best to keep it running cost-effectively. If you’ve had frequent, costly repairs, the best option may be a replacement.

If you need HVAC repairs, replacement, or maintenance services, Rick’s Heating & Cooling is here to help. We’ve been the trusted HVAC company in the Cincinnati area for over 35 years. Our trained technicians practice industry-best HVAC service and repair protocols.

Call 513-899-6005 or contact Rick’s Heating & Cooling for indoor air quality solutions and HVAC service or repair.