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posted 07-15-2017 09:51 PM

5 replies so far

View clin's profile


1121 posts in 1852 days

#1 posted 07-15-2017 10:08 PM

You want as fine a particle filter as the blower can handle. For a given particle size, the more surface area of the filter, the less back pressure it will create for the blower. Less back pressure means more air movement.

In order to engineer this, you would need the pressure and flow rate curve of the blower. Filter materials have a similar rating. So for a given filter and size, you would know its back pressure per flow like PSI/CFM. Where this intersects the blower curve is where it will operate.

But I’m going to guess you don’t have that info for the blower. In that case, you want the filter surface area as large as you can make it. Then I would start with a HEPA equivalent filter and see how it works. If the blower moves a lot less are with the filter(s) installed, then you need a filter that allows more airflow and that will also mean larger particles will get through.

Or you can go the other way and start with a course filter and work up to a finer filter.

Also, best to go two stage. First filter is course, like common furnace filter, and will trap all the big stuff you can see. This will need to be cleaned and changed often. Have another filter after this for the really fine stuff (HEPA filter or similar). It will not need to be changed that often.

Also, think outside the box. There is no reason the unit has to be a cube or box shape. So instead of have just one filter flat on one side, use two filters, joined on one edge, folded to form a shape like a pup tent. You can double the surface area of the filter. Yes it means twice as many filters, but also, they will clog or fill twice as slow.

But you will have much freer airflow for longer this way.

You could even create more than two surfaces for the inlet side. For example, make a box with 5 sides that hold filters on each side (5 filters), Butt the open side of box this up to the intake side of the blower box. Then the blower will be drawing air through 5 filter surfaces giving you much, much more surface area than just the size of the blower inlet.

You can extend this concept as much as you want.

Hope that made some sense.

-- Clin

View Robert Keeney's profile

Robert Keeney

89 posts in 4368 days

#2 posted 07-15-2017 11:48 PM

You might want to watch this video. I would at least double the filters putting a coarse cheap filter on the outside. Some people will put three progressively finer as you go in. saves on filter costs.

-- Robert in Tallahassee Florida,

View hairy's profile


3109 posts in 4388 days

#3 posted 07-16-2017 02:32 AM

Here’s what I did.

-- Genghis Khan and his brother Don, couldn't keep on keeping on...

View SignWave's profile


472 posts in 3891 days

#4 posted 07-16-2017 03:56 AM

I made mine using 1” filters. the 4” filters have more surface area, but are a lot more expensive. I built my box oversized so I could have the maximum number of filters. Mine uses 4- 20” x 20” filters so I have around 11 square feet of filter surface (not counting the pleats in the filters). That’s a lot, but if you’re creative in the way that clin already suggested, you can get a design that maximizes surface area. My blower moves A LOT of air, and I use it as a way to keep cool in the summer as well.

I use inexpensive filters and change them often. I get the cheapest paper filters they have at HD, not the woven kind that you can see through. When they’re new, I presume that they let microscopic particles pass through, but as a layer of dust starts to form on them, they will actually filter smaller particles (and reduce airflow somewhat). I share your attitude that it’s so much better than nothing that I am not going to worry about whether I have a 99.0% solution vs. a 99.5% solution.

When I look at how much dust there is in my filters, I marvel at how much dust I am no longer breathing. I can absolutely tell the difference, and my wife says I snore (a little) less.

-- Barry,

View woodbutcherbynight's profile


6187 posts in 3265 days

#5 posted 07-16-2017 02:45 PM

Take a look at this video. Was helpful in designing my air cleaner.

-- Live to tell the stories, they sound better that way.

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