Why is My Air Filter Black?

Your air filter is an essential part of your furnace and air conditioner. It is also the part that is most often forgotten about. Like the rest of your HVAC equipment, it’s out of sight, out of mind.

But you’ve just remembered that you haven’t changed it in a few weeks. So you go downstairs to replace it with a new one. When you remove it from the furnace, you see that’s it’s black.

Black? That can’t be right, can it?

A black air filter is a sign that something is amiss in your furnace, air conditioner, or home. If you do have a black air filter, check for any of these causes.

1. Carbon Monoxide

One of the first things you should do if you have a black air filter is to check for carbon monoxide. In high concentrations, carbon monoxide is dangerous to your health, and could even be deadly.

When gas or exhaust fumes leak in your house, carbon monoxide can leave a soot-like appearance on your filter. Otherwise the gas is colourless and odorless. The problem could be coming from the furnace itself, or somewhere else in the house.

Call a professional if you suspect there’s a problem with your furnace, before it becomes a bigger one.

2. Mold

When you run your air conditioner, the evaporator coil will become damp from condensation. If left for a long period of time, that condensation will mix with the dust and dirt and form a black mold. This mold will grow and eventually spread to your furnace, and the filter.

Mold can also occur in your ducts, particularly in parts of your home that are exposed to damp conditions, like a basement. After the wet summer we’ve had, it’s a good idea to check, no matter the colour of your air filter.

Regular maintenance and cleaning will help keep mold out of your HVAC equipment, and ensure that it won’t cause your air filter to turn black.

3. Excess Amounts of Dirt and Debris – Including Soot

The main purpose of your air filter is to catch the dust particles and other debris in the air. The more there is, the quicker your air filter will become clogged.

If you don’t regularly check your furnace filter often, the sheer amount of dirt could make the air filter black.

This is especially true if you burn candles or have a fireplace. They spread smoke and soot into the air, which can settle on the filter. If it looks as black as soot, and you really like your scented candles and lounging by the fire, it may be black because of soot.

If you have a black air filter, first look for black soot and mold. If you have neither, try abstaining from candles, and increasing the amount of times you dust. When you check your filter again, you should see a difference.

Tip: If you’re still having problems with excess dust and allergens, it might not be your furnace’s fault. We have several air quality products that could help get the air inside as fresh as the air outside.

4. Improper Air Flow

Sometimes your venting system can become overly clogged or even leak. This leads to improper combustion in your furnace, which can leave a black buildup on your air filter.

If you suspect that your venting system isn’t work properly, call us to come look into the problem. It’s always better to be safe than sorry.

Replace or Clean Your Air Filter Every 30 Days

The more clogged your air filter is, the harder your furnace has to work to properly heat your home. This causes your furnace to use more energy, which costs you more money. It also won’t properly filter your air for dirt and debris.

We recommend checking your air filter every 30 days. If needed, replace or clean the filter. You shouldn’t go more than 3 months without changing your air filter.

How to Replace Your Air Filter

Replacing your air filter is a simple procedure that won’t take a lot of time. Once you purchase a new filter that is the correct size for your furnace, carefully remove the old one, making sure not to jar any excess dirt loose.

Slide the new one into the frame, and there you go! It only takes a few minutes, and your furnace will filter air and heat your home efficiently.

If you have a reusable filter, this will take a bit more work. You’ll have to carefully clean it with a vacuum, or with water. Let the filter dry completely before placing it back into the frame.

If You’re Not Sure What’s Wrong, We’ll Be Able to Help

Furnaces can be overwhelming if you aren’t familiar with how they work, and finding a black air filter doesn’t help.

If you aren’t sure what the problem is, we’ll help you figure it out.

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