Cheap HEPA Air Filter

Recently I've started having allergy problems, but the HVAC air filter was on the ceiling (beyond most dust), and did not want to spend much money on an expensive HEPA room filter.  So, I just taped a high efficiency air filter onto a ordinary box fan.  Cost is $10-$40, depending on materials on hand and how much you want to spend on the filter.

Materials:
*** 1 - Box fan, 20"x20".  Generally the bigger the better, since at low speeds, the fan is quieter and the filter is more efficient.
*** 1 - High Efficiency filter, 20"x20", or what ever fits your fan. I doubt that a top-of-the-line filter is worth the extra money for ordinary dust and allergens, so got the next grade lower.  (about $10 at Lowes).
*** Duck-tape.  Or Duct-tape.  Since air filters are supposed to be changed at least every 3 months, the tape will be temporary, so cheap is good, and must be wide enough to span the gap and make an air tight seal between the edge of the filter and the body of the fan

Note that the filter should be mounted so the air flows through it in the indicated directions.  I installed my filter on the intake side to keep the fan itself cleaner, and (more importantly) to ensure that the air flow is evenly distributed across the surface of the fan.

Comments

[DennisSweitzer]

Testing & recommendations from the EPA. They specifically address wildfire smoke, but much applies to filtering out COVID viruses (use filters rated at least Merv 13).
Also, I've switched to 4" filters which last longer and restrict the airflow less.
https://www.epa.gov/air-research/research-diy-air-...

[ShannonS15]

That's great! I had a similar idea, so I googled make an air filter. Currently Missoula is in a deep smoke season this year. So I thought to filter a bit of that out. Making this today, I already have the box fan and duct tape. Thanks alot!!

[DennisSweitzer]

Great! Let us know how well it works.

[mole1]

this looks like a really good idea. Does the fan get hot sucking through the filter?

[denswei]

Not all. It really does not affect the flow of air very much, although I suppose it might as the filter collects dust.

I usually weigh my filters on a triple beam balance before & after, so it will be interesting to see how much dust it collects.

[isven9000]

Denswel, any interesting data on the weight of your filters?

[DennisSweitzer]

I just weighed my kitchen air filter and it gained about 12 grams of dust in 7 months. This time I did not tape it onto the fan. (NB: yes, it's obviously way past the recommended 3 month limit).

[DennisSweitzer]

I wouldn't describe it as 'interesting', but I finally changed this one and it gained 3.4 grams. Unfortunately, the tape took off some of the paper, so that's a minimum…. I'd guess 4-5 grams.
Now I just put the filters against the fans and let the suction hold them on: I have one in the kitchen (near the ceiling), and 2 others around the house.

[DennisSweitzer]

Not yet. I just moved into a new house, so should do that.
The place has a gas log fireplace, so filter hasgotten rather black from the soot (until I got the settings right for the damper).

[DennisSweitzer]

Whenever I have a dirty project in the house, I set up a fan&filter next to it to catch the dust before it disperses. According to the filter specs, it should catch mold spores as well (for extra piece of mind when drying out a basement plumbing leak!)
I try to remember to set one up when vacuuming as well….
After a year, I'm quite happy with the results….

[AthleticTrainer]

Had this idea the other day, glad someone else has tried it lol. In regards to your HVAC air filter, the "change every 3mo" is a general guideline. I find when I start waking up with allergies I will change the filter and my allergies go away. Sometimes that's every 3 weeks or even monthly. I started doing this when I moved to FL and started getting really bad allergies and our HVAC started working much better too. Thanks for the post!