As an Amazon Associate I earn from qualifying purchases.Updated: March 27, 2026
The Furnace Filter in your Lennox S20i unit plays a crucial role in trapping dust, dirt, and other airborne particles. Over time, these filters accumulate debris and become less effective, restricting airflow and potentially damaging the furnace's components. Regularly replacing the filter ensures clean air circulation and efficient operation of your heating system. Neglecting replacement can lead to reduced performance, higher energy bills, and even premature failure.
Function: Traps dust, dirt, and other particles to protect your furnace and ensure clean airflow.
Signs it needs replacing: Reduced airflow, increased energy bills, unusual noises from the furnace, visible accumulation of dirt on the filter.
OEM vs aftermarket: OEM parts guarantee exact fit and quality but are typically more expensive. Aftermarket filters are often more affordable, but compatibility with your specific model (S20I-036) needs to be verified.
Installation: Replacing the Furnace Filter is generally straightforward. Simply turn off the power to the furnace, remove the old filter, and insert a new one in the same direction.
Replacement schedule: every 1 month
Compatibility warning: always verify part number matches your exact model before ordering
Pros & Cons
Pros
✓ Restores device to original performance without buying a new unit
✓ Significantly cheaper than a full device replacement
✓ Multiple options available from OEM and aftermarket sellers
Cons
✗ OEM parts cost more than third-party alternatives
✗ Wrong part number will not fit — model verification is essential
Common Use Cases
Scheduled maintenance on the every 1 month replacement cycle
Performance restoration after noticing reduced output or efficiency
Preventive replacement before a worn part causes secondary damage
Who Should Buy This
This filter replacement guide is for Lennox S20i owners experiencing reduced heating performance or who want to perform scheduled maintenance.
Not ideal for: If your furnace is frequently breaking down, making unusual noises, or showing signs of severe damage, a full device replacement might be necessary.
Good to Know Before Buying
💡
Always confirm your exact model number (S20I-036) before ordering. Part numbers vary between model variants and production years. Check the label on your device or original documentation to be sure.
Frequently Asked Questions
What is the part number for the Lennox S20i Furnace Filter?
The part number is LCN1500M. Always verify this matches your exact model (S20I-036) before ordering, as similar models may use different parts.
How often should I replace the Furnace Filter on my Lennox S20i?
every 1 month
Will aftermarket Furnace Filter replacements work in my Lennox S20i?
Third-party parts are widely available and often cheaper than OEM. Look for listings that specifically mention compatibility with model S20I-036 and check buyer reviews for fit confirmation before purchasing.
Prices change frequently. See the latest deal on Amazon.