Symptoms
- Filter looks gray, matted, or covered in dust and pet hair
- Weak airflow from vents
- Furnace short cycling or running longer than usual
Likely causes
- CommonFilter overdue for replacementStandard filters typically need replacing every 1–3 months depending on household dust and pets.
- PossibleWrong filter thickness or MERV rating restricting airflowA filter that's too restrictive for the system can choke airflow even when new.
- PossibleRenovation or construction dust overwhelming the filter earlyDust from remodeling clogs filters far faster than normal use.
What to do
- Turn the furnace off before removing the filter.
- Slide out the old filter, noting the airflow direction arrow printed on its frame.
- Hold it up to a light; if you can't see light through it, it needs replacing.
- Insert the new filter with the airflow arrow pointing toward the furnace, matching the old one's orientation.
- Write the install date on the new filter frame with a marker to track replacement timing.
- Set a recurring reminder to check it monthly and replace every 1–3 months.
Tools and parts
Furnace air filter, correct sizeSearch: “furnace filter size MERV replacement”
When to call a pro
This is a simple DIY task; a professional is only needed if the filter housing itself is damaged or hard to access.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.