What is the dirty side of an air filter?

Return Air filter’s “black” or “dirty” Side Faces the Incoming Air – usually that’s the room side. If you are installing the filter in a return register, then the “black” side of the filter is receiving “dirty” air (dusty air from your room) so it would be facing the room.

What happens if air filter is backwards?

By installing your filter backwards, air will have a harder time flowing through the filter and your air handler will have to work harder to make up for the loss of airflow. This could lead to higher utility bills and possibly damage your furnace or air conditioner.

How dirty should an air filter look?

1) Your Air Filter Looks Dirty

If your air filter is clean, it should be white or off-white. Over time, as dust and dirt accumulate on it, the air filter will get darker and the dirt will be noticeable. When it starts looking dark and grimy, you might be due for a replacement.

Does the arrow go up or down on an air filter?

The arrow on the filter should always point toward the furnace. The furnace or the filter air box most likely will contain the correct filter measurements for replacement filters or just check the filter itself.

Which side of furnace filter should be dirty?

In all cases, the furnace filter should be dirty on the side that the air comes into the furnace from. If your air filters are dirty in some other fashion, it is likely your furnace is not working properly, or the filter was installed incorrectly.

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