Protects All Against
21x21x4 Air Filter
AC Furnace Air Filter 21x21x4 -Inches
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Item Model Number: FKFB21X21X4
Brand: Filter King Filter size: 21x21x4 Actual Size: 20.5 x 20.5 x 3.75 4-Inch Filter MERV 8 Filter Rating Protection From: Pollen, Dust, Mold, Dust Mites, Bacteria, Pet Dander, Smoke, Viruses Residential / Commercial Use
Item Model Number: FKFA21X21X4
Brand: Filter King Filter size: 21x21x4 Actual Size: 20.5 x 20.5 x 3.75 4-Inch Filter MERV 11 Filter Rating Protection From: Pollen, Dust, Mold, Dust Mites, Bacteria, Pet Dander, Smoke, Viruses Residential / Commercial Use
Item Model Number: FKFD21X21X4
Brand: Filter King Filter size: 21x21x4 Actual Size: 20.5 x 20.5 x 3.75 4-Inch Filter MERV 13 Filter Rating Protection From: Pollen, Dust, Mold, Dust Mites, Bacteria, Pet Dander, Smoke, Viruses Residential / Commercial Use
Manufactured in the US
Why Buy Air Filters From Filter King?
In comparison to fiberglass filters, 21x21x4 pleated air filters are at least 20 times more effective. All Filter King air filters are made in the US.
Filters frames are made out of heat resistant paperboard with horizontal grid supports. Able to withstand temperatures of up to 200° F and resistant to moisture, the paperboard frames do not support microbial growth and outperforms traditional cardboard frames.
Chemical free, electrostatically charged synthetic polyester media is pleated, maximizing the surface area, to capture a high number of airborne particles as small as 0.3 microns with low air flow resistance. To increase durability, the media is supported with a corrosion resistant steel wire.
21x21x4 Air Filter Reviews
What MERV Rating should I choose?
How Often to Change Your 21x21x4 Air Filter?
Filter King AC & furnace filters aren’t the typical fiberglass filters that need to be replaced every 30 days. Our filters can typically be used for 3 to 5 months before requiring to be changed. Naturally, a variety of things influence filter lifespan.
Some of the factors that influence your filter’s life include outdoor air quality, whether pets are in the home, and how well your HVAC system is maintained.
Your air filter becomes clogged over time by trapped particles, preventing airflow. The efficiency of the HVAC filter declines. Your system must work harder to heat and cool your home. The extra strain on the HVAC system causes higher energy bills. Regular home air filter replacements can prevent expensive system repairs or replacements down the road.
You should change your filter more frequently if you notice:
- Household dust build-up
- The air isn’t cooling as is used to
- There’s more dust near the air vents
- A dirty filter surface
- Higher energy bills
- Burning smells near your HVAC system.