21.25x21.25x4 Air Filters

Preloader
MERV 8 (Standard)
MERV 8
MERV 8 Badge
3 Month Badge
3 Month Filter

1. Select Filter Quality (Help Me Choose)

Learn More
Learn More
Learn More

2. Select Filter Quantity (Ordering multiple sizes? Try Quick Order)

Need more than one size? Try Quick Order

3. Select Delivery Method

Details on recurring orders
Save 5% with Auto Delivery

21.25x21.25x4 Air Filter Description

Actual Size: 21.25x21.25x4"
Model: AFB21.25x21.25x4M8A
Available In MERV Rating: 8 , 11 , 13
Made in the USA
Ships in 24 hours
Add To Cart
Made inthe USA
Filterbuy ships replacement air filters in 24 hours iconShips in24 Hours
Why Filterbuy Air Filters?
Long-Lasting

FilterBuy filters are designed to last up to 90 days, 3 times longer than fiberglass filters. If you have pets, kids, or allergy sufferers in your home or business, replace your filters more often to maintain superior indoor air quality and keep your energy costs low.

installing a new air filter
all air filters are manufactured by Filterbuy in the USA using all American made components
Made In The USA

All air filters are manufactured by FilterBuy in the USA using 100% American made components. By purchasing directly from the manufacturer, you’re saving big on a premium product.

all air filters are manufactured by Filterbuy in the USA using all American made components.
High Quality

21.25x21.25x4 pleated air filters are at least 20 times more efficient than fiberglass filters. Filter frames are made of beverage board, which stays strong through humidity and temperatures up to 200° F. Synthetic media provides significantly higher particulate efficiency than standard cotton media.

diagram of how an air filter purifies dirty air

21.25x21.25x4 Air Filter Reviews

Is it Time to Change Your Filter?

Generally, we recommend you replace your air filters every 90 days. Find out below if you should change your filters more often.
If someone in your home has asthma and/or allergies...
Change your filter every 6 weeks to ensure indoor air quality is at its best.
If you have pets...
Change your filter every 2 months to avoid shedding and odor buildup.
If you have young children...
Change your filter every 2-3 months, as having clean air is even more important with children in your home.
Rolling
x

Build a Custom Size

Simply measure the length and width of your filter with a tape measure and choose the closest size (to 1/8”) in the drop down menu. 1/8” tolerance is standard and should not cause a problem in any standard filter application.

Please note that the ‘actual’ filter size, ie the size that your tape measure shows, should be used when creating a filter with this tool, not a nominal filter size. Note that the depths of each filter are standard, as shown to the right.

Simply measure the length and width of your filter with a tape measure and choose the closest size (to 1/8”) in the drop down menu. Please note that the filter depth is standard.