Picture of DIY Replacement AIR Filters
Own one of those room sized plug in air purifiers? Sick of paying $10-$100 per filter? We were too, so we decided that we could save money and get a better filter.

HEPA Filters are made for clean rooms and easily clog up in a home environment. After reading many studies done on filters, we've concluded that getting a furnace filter is the best choice. Today there are plenty of sub-micron grade furnace filters, and luckilly for us, they are all priced based on micron size (so get the biggest one you can with the highest filtration rating possible.)

Also doing this seems to create a better air path (blocks off any cracks that air can bypass the filters with, as they are usually designed to do - as HEPA plugs up and that'd wear the motor out.

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Step 1: Materials List

Picture of Materials List
You'll need:
-A "flat" filter based air cleaner, technically any of them work that I've tried (all of them were holmes brand but others seem like they'd work)

-Allergen grade furnace filter (all of them are priced by how small of particles they filter, not by size. GET THE BIGGEST ONE of the rated filtration you desire to use)


-Duct tape


-Tape Measure

-Card Board

-Gloves (to keep your hands from getting cut on the mesh)

Step 2: Make a template for future use

Picture of Make a template for future use
We'll be making a cardboard template (not totally necessary, but we think its best so you can lay out the best way to cut up your jumbo filter and so you have it for the future and don't need to measure it again.

Take your old filter out of the machine, and put it on the cardboard. Trace, and cut out. You can make more for each of your filters to make sure you get enough for everything, or just use one.

Cut this out when you're done.

Step 3: Known Filter Sizes

Picture of Known Filter Sizes
Here are the filters that I know of, and their sizes:

Holmes G Filter (HAPF21)

Holmes E Filter (AOR115, AOR118, HAP115)
6" Square

Holmes "625" (replaces the mutliple filters in the unit with one) (HAP625)

If anyone knows more, feel free to comment and I'll add them.
sunsetlover85 months ago

Hi, I was wondering, if I use something like the 3M Purple 1500 Filtrete, do I need an activated carbon pre-filter? Also on my HEPA Panasonic machine, they place the deodorant filter (it's really a black carbon filter) after the HEPA filter(!). Any ideas?

dchall86 years ago
My new car has a "cabin filter." I want to do something like this to replace that filter, too. Thank you.
hypercube33 (author)  dchall86 years ago
Mine does as well. I cut out the edge piece of the filter, and it works beautifully.