How Often Should You Replace Lennox Filters 20x25x5?
If you’re using a 20x25x5 Lennox air filter and can’t remember the last time you changed it, that filter could be silently choking your system’s airflow — and your energy efficiency. Based on our hands-on experience, we’ve seen everything from premature blower motor failures to skyrocketing utility bills simply because a filter was months past due. In this guide, we’ll show you exactly how to spot the major signs it’s time for a replacement, explain why it’s more than just a maintenance chore, and walk you through how to swap it out the right way — without risking damage to your system.
Top Takeaways
• A dirty 20x25x5 Lennox filter can restrict airflow and raise energy bills.
• Replace it every 3–6 months (more often with pets or allergies).
• Neglect can cause costly damage like blower failure or coil issues.
• Follow airflow arrows when installing a new filter.
• A $40 filter change can save thousands in repair or system replacement.
Signs It’s Time to Replace Your Filter
If your Lennox system feels sluggish, your airflow has weakened, or you’ve noticed more dust around your vents, your air filter may be overdue for replacement. Based on our on-site inspections across hundreds of Florida homes, we often see filters that haven’t been changed in 6–12 months, well past their recommended lifespan. Other red flags include:
• Unusual odors when the HVAC runs
• Increased allergy symptoms indoors
• The system is running longer to reach the set temperatures
Why Changing the Filter Really Matters
Your 20x25x5 filter doesn’t just trap dust — it protects your HVAC system from harmful buildup and helps maintain healthy air quality. A clogged filter can force your system to work harder, leading to higher energy bills, reduced comfort, and even premature equipment wear. In some Lennox systems, neglecting filter changes has led to coil damage or blower motor issues that cost thousands to repair.
How to Replace It the Right Way
To safely replace your Lennox filter:
1. Turn off the system completely at the thermostat.
2. Locate the filter housing, often found near the air handler or return vent.
3. Slide out the old filter and check the airflow arrow on the frame.
4. Insert the new 20x25x5 filter with the arrow pointing in the correct direction.
5. Power the system back on and check for proper operation.
Pro tip from our techs: Always note the install date on the new filter — and set a 3- to 6-month reminder based on your home’s usage, pets, and indoor air needs.
"After inspecting hundreds of Lennox systems in the field, we’ve found that a neglected 20x25x5 air filter is one of the most common — and costly — oversights. A simple filter swap every few months can prevent system strain, protect indoor air, and save homeowners from expensive repairs down the line."
Real-World Case: A Clogged Filter Nearly Shut Down This Lennox System
Location: Boynton Beach, FL
System: Lennox EL296V
Problem: Uneven cooling + high energy bills
What We Found
• The filter (20x25x5) hadn’t been changed in 10+ months
• Clogged with dust, pet hair, and debris
• Airflow is restricted by 60%
• Blower motor overworked
• The system kept tripping the high-limit switch
What We Did
1. Replaced the filter with a high-efficiency MERV option
2. Cleaned the evaporator coil
3. Reset the system
4. Set a reminder schedule with the homeowner
5. Explained how to monitor the filter condition between changes
✅ Results
• Airflow was fully restored within 24 hours
• 23% drop in energy usage (verified via utility bills)
• No further system trips or issues for 6+ months
• Improved indoor air quality — fewer allergy complaints
Why Replacing Your Filter Matters — Backed by Real Data
We've seen it firsthand: dirty filters drive up costs, reduce air quality, and damage HVAC systems. These stats prove it.
1. Dirty Filters Hurt Air Quality
• Clogged filters trap dust, dander, and mold.
• Worsens asthma and allergy symptoms.
• EPA confirms high-efficiency filters improve indoor air health.
• EPA
2. Higher Bills, More Strain
• Blocked airflow = longer run times.
• Systems overwork, driving up energy costs.
• CDC warns that poor filter maintenance reduces energy efficiency.
• CDC
3. System Lifespan Shrinks
• We’ve replaced motors, coils, and even full systems due to old filters.
• ASHRAE recommends regular filter changes to prevent damage.
• ASHRAE
Final Thought & Expert Opinion
A $40 filter can save your $4,000 system — we’ve seen it firsthand.
What We’ve Observed:
1. Most major HVAC issues start with filter neglect.
2. Dirty filters cause gradual system decline, not instant failure.
3. Homeowners often notice:
• Hot or uneven rooms
• Higher energy bills
• More dust and allergy symptoms
Based on Field Experience:
We’ve serviced hundreds of Lennox systems. Here's what we’ve learned:
1. Skipping filter changes shortens system lifespan.
2. Clogged filters force your HVAC to work harder = wasted energy.
3. Clean filters = better air, lower bills, fewer repairs.
Our Honest Take:
• Filter changes aren’t just routine — they’re preventive protection.
• It’s the most affordable way to safeguard your system and indoor air.
• Don’t wait for a breakdown to act — set reminders, stay proactive.
Final Word:
Replacing your Lennox air filters 20x25x5 on time helps ensure:
✅ Cleaner air
✅ Lower operating costs
✅ A longer-lasting HVAC system
Next Steps: What to Do Right Now
Follow these simple steps to protect your system and improve air quality:
1. Check Your Filter
• Turn off your HVAC.
• Locate and remove the 20x25x5 filter.
• If it's dirty, bent, or over 90 days old, replace it.
2. Replace It Properly
• Use a MERV-rated filter made for Lennox systems.
• Follow the arrow for the correct airflow direction.
• Insert it securely and restart your system.
3. Set a Reminder
• Replace every 3–6 months.
• More often, if you have pets or allergies.
• Use a calendar, app, or smart home alert.
4. Save This Guide
• Bookmark this page for easy reference.
• Share with family, roommates, or tenants.
5. Call a Pro If Needed
• Unsure which filter fits?
• Not comfortable changing it yourself?
• Book a certified HVAC tech to help.
Frequently Asked Questions
1. How often should I replace my Lennox 20x25x5 air filter?
Most homeowners should replace it every 3 to 6 months. If you have pets, allergies, or run your system constantly, replace it every 2–3 months for best performance.
2. What happens if I don’t replace the air filter on time?
A clogged filter restricts airflow, causing your system to overwork, reduce efficiency, and spread dust and allergens. It can also lead to expensive damage to the blower motor or evaporator coil.
3. How do I know if my Lennox filter needs replacing?
Look for these signs:
• Reduced airflow from vents
• More dust in your home
• Increased energy bills
• Musty or unusual odors
If in doubt, pull it out — and check for discoloration or visible buildup.
4. Can I replace the Lennox 20x25x5 filter myself?
Yes. It’s a simple DIY task:
1. Turn off the system.
2. Slide out the old filter.
3. Insert the new filter with the airflow arrow pointing in the correct direction.
4. Power your system back on.
Just make sure to buy the correct size and MERV rating for your unit.
5. What’s the best filter to use for a Lennox system?
Use a Lennox-compatible 20x25x5 filter with a MERV rating between 8 and 13. Higher MERVs trap smaller particles but may reduce airflow if not matched to your system. Check your owner’s manual or consult a technician for the best fit.
Learn more about HVAC Care from one of our HVAC solutions branches…
Filterbuy HVAC Solutions - Miami, FL - Air Conditioning Service
1300 S Miami Ave Apt 4806 Miami FL 33130
(305) 306-5027
