How to Furnace Filter Check
During heating season, your furnace works overtime, and its filter accumulates dust, debris, and particles much faster than during milder months. This monthly check involves removing and inspecting the filter to assess whether it needs replacement. A clean filter ensures adequate airflow to prevent the furnace from overheating, maintains energy efficiency, extends equipment life, and keeps your indoor air clean during the months when your home is sealed up tight against the cold.
Cost to Skip This Task
Risk $100 – $3,000 in repairs
Why It Matters
During heavy winter use, furnace filters clog faster. A clogged filter restricts airflow, making your furnace work harder, increasing energy costs, and potentially causing the heat exchanger to overheat and crack. Check monthly during heating season (October-March in most climates). Replace when visibly dirty or at least every 90 days. With pets or allergies, replace monthly.
Safety First
- Turn off the furnace before checking or replacing the filter
- Wear a dust mask when handling dirty filters
What You'll Need
Supplies
- Replacement furnace filter$15
Step-by-Step Instructions
Before You Start
Know your filter size. During peak heating season, filters may need monthly replacement depending on usage and conditions.
- 1
Turn off the furnace at the thermostat
- 2
Locate the filter (usually in the return air duct or furnace cabinet)
- 3
Slide out the filter and inspect it
Hold it up to a light source - if you cannot see light through it, replace it
- 4
If dirty, replace with a new filter of the same size and rating
- 5
Ensure the airflow arrow points toward the furnace
- 6
How to Verify Success
Filter is clean or freshly replaced. Furnace runs normally with good airflow from vents. No unusual noises.
When to Call a Professional
- Furnace is short-cycling (turning on and off frequently) - diagnostic $75-150, repair $150-600
- You hear banging or unusual noises from the furnace (inspection $100-200, blower motor $300-600)
- Some rooms are not heating properly even with a clean filter (duct inspection $200-400, balancing $300-500)
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