Quick Answer
In Charlotte's climate, change your HVAC air filter every 30-60 days during heavy use seasons (summer/winter). Use MERV 8-11 for the best balance of filtration and airflow. Higher isn't always better—MERV 13+ filters can restrict airflow and strain your system. Check your filter monthly and replace when visibly dirty.
Your air filter is the most important maintenance item you control—and the most neglected. A dirty filter is the #1 cause of AC problems we see in Charlotte. It costs just $5-20 to replace, but ignoring it can lead to hundreds in repair bills or even system failure.
This guide covers everything: filter types, MERV ratings explained, how to find your size, and how often to change it in Charlotte's demanding climate.
What Does Your Air Filter Do?
Your HVAC filter serves two purposes:
- Protects your equipment – Keeps dust, debris, and particles from coating internal components
- Improves air quality – Removes allergens, dust, and particles from circulated air
The Real Cost of a Dirty Filter
MERV Ratings Explained
MERV (Minimum Efficiency Reporting Value) measures filtration effectiveness. Higher numbers catch smaller particles—but there's a tradeoff.
| MERV Rating | What It Catches | Best For |
|---|---|---|
| MERV 1-4 | Large particles, pollen, dust mites | Minimal filtration (not recommended) |
| MERV 5-8 | Mold spores, pet dander, dust | Most homes (good balance) |
| MERV 9-12 | Fine dust, legionella, humidifier dust | Allergy sufferers, better IAQ |
| MERV 13-16 | Bacteria, tobacco smoke, sneeze droplets | Hospitals, labs (may restrict airflow) |
Our Recommendation: MERV 8-11
Filter Types Compared
Fiberglass (Disposable)
The cheapest option ($1-5). Captures large particles but provides minimal filtration. MERV 1-4. Better than nothing, but not recommended if you care about air quality or system protection.
Pleated (Disposable)
The best choice for most homes ($5-20). Pleated design increases surface area for better filtration without excessive restriction. Available in MERV 8-13. This is what we recommend for most Charlotte homeowners.
Electrostatic (Washable)
Reusable filters you wash monthly ($30-100 upfront). Use static charge to attract particles. Convenience of not buying replacements, but require consistent cleaning to work properly. MERV 4-10.
Media Filters (High-Capacity)
Thick (4-5") filters installed in a special cabinet. Last 6-12 months between changes. Higher cost ($25-50) but excellent filtration and less frequent maintenance. Great for busy homeowners or those with allergies.
How to Find Your Filter Size
Finding Your Size
- 1
Check the existing filter
The size is printed on the filter frame (e.g., 20x25x1 or 16x20x4).
- 2
Measure if needed
Measure length x width x depth of the filter slot. Round to nearest inch.
- 3
Note: Nominal vs. Actual
Filter sizes are "nominal" (rounded). A 20x25x1 filter actually measures about 19.5x24.5x0.75".
Common residential sizes: 16x20x1, 16x25x1, 20x20x1, 20x25x1, 20x25x4, 20x25x5. If your size seems unusual, measure carefully—some systems use non-standard sizes.
How Often to Change Your Filter in Charlotte
Charlotte's climate—hot, humid summers and moderate winters—means your HVAC runs hard most of the year. Our recommended schedule:
| Season | Recommended Interval | Why |
|---|---|---|
| Summer (May-Sept) | Every 30 days | AC runs constantly, high pollen, humidity |
| Winter (Dec-Feb) | Every 30-45 days | Heating runs frequently |
| Spring/Fall | Every 45-60 days | Moderate use, but high pollen in spring |
These are guidelines. Check your filter monthly and change when it looks dirty—even if it hasn't been a full month.
Factors That Require More Frequent Changes
- Pets (especially dogs/cats that shed)
- Allergies or respiratory conditions
- Dusty home or nearby construction
- Smokers in the household
- More than 3 occupants
- Windows frequently open
How to Change Your Air Filter
Filter Replacement Steps
- 1
Turn off HVAC system
Switch thermostat to OFF before changing filter.
- 2
Locate filter slot
Usually in return air vent (wall/ceiling) or at air handler/furnace.
- 3
Remove old filter
Slide out carefully to avoid releasing trapped dust.
- 4
Check airflow arrow
New filter has arrow showing airflow direction—point toward blower/furnace.
- 5
Insert new filter
Slide in with arrow pointing correct direction. Should fit snugly.
- 6
Turn system back on
Switch thermostat back to your normal setting.
Signs Your Filter Needs Changing
- Filter looks gray/dark (hold up to light—if you can't see through, change it)
- Reduced airflow from vents
- System running longer than usual
- Increased dust on surfaces
- Allergy symptoms worsening
- Higher energy bills
- System short-cycling (turning on/off frequently)
Common Filter Mistakes
- Installing backward – Airflow arrow must point toward blower
- Using wrong size – Gaps let unfiltered air bypass
- Buying highest MERV available – Can restrict airflow, strain system
- Waiting too long to change – Leads to system problems
- Forgetting entirely – More common than you'd think
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Written by
Kodiak HVAC Team
HVAC professional at Kodiak Heating & Cooling.