Building A Homemade HEPA Filter System

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Automotive Prefilters!!! -    
Pro's Debate: HEPA, Gloveboxes, Oven Tek  -    
Homemade Bucket HEPA filter     Fungusmaximus
5 Minute Flow Hood     Molester
Clean Room  -    
Flow Hoods & Glove Boxes  -    

By Admin (Admin) on Thursday, August 23, 2001 - 11:47 am:

I use a filter system that allows me to do some sterile transfers without having to worry about some of the problems associated with infections. However, for me to build an actual HEPA filter system would have been too expensive because the HEPA filters themselves are very expensive. I have built what I call a Homemade HEPA filter system that cost less than $100.00 everything that I needed to get. This document will list all the things that you will need to build entire system.

What you need:

4 Standard Furnace Filters (about a buck each)
1 3M Filtrete Furnace Filter (about $15.00)
1 HEPA Furnace Filter (about $25.00)
1 Furnace Fan with a plug
1 4'x8' piece of 3/4" plywood
100 1 1/2" sheet rock screws
1 tube Silicone sealer
1 Roll Duct tape

Most of these things you can get at a local home improvement store. The furnace fan you may have to get at a salvage yard. I have seen the fans new but they are rather expensive and if you look you can get one for cheap.

Preparing the Filters:

When you purchase the filters, make sure that you get them all the same outside dimension. I was able to get all the filters 20"x25". Tape the filters so they are sandwiched together starting with the El Cheapo filters first, followed by the 3M Filtrete, then the home HEPA filter. Seal the edges well with the duct tape because you want no air to get by them. There are arrows pointing the direction that the air is supposed to flow. You want the arrows pointing the same direction. Here is a simple way to remember the order that you need to put the filters in: Cheapest to most expensive.

Construction of the box:

I constructed the box from a piece of plywood that I had on the garage. This was the cheapest that I could find. First you want to measure the final outside dimension of the filter. This may not be the printed dimension of the filter because they are manufactured smaller than what is printed on the filter. My filters were about 1/2 inch smaller than what was printed on the filter. The opening of the box was 24 1/2"x19 1/2" to accommodate the filter. I decided that the depth of the box should be 18 inches. This would allow for 6 inches of filter and 12 inches of plenum. The plenum is the space that the fan will force the air into.

Then seal the joints of the box with the silicone sealer. This will ensure that more air will be going through the filter and not through any holes.

After I constructed the box, I made a hole for the fan. It was on the top of the box and the outlet of the fan forced the air parallel to the filter. This is a recommended setup for a professional HEPA design. The air that is forced into the plenum will have equal pressure out of the filter.

I secured the filters in the box with more duct tape. This worked very well because I was able to add tape to the areas that had air leaking through some of the seams. Remember, YOU WANT THE MOST EXPENSIVE FILTER TO BE THE LAST ONE THAT IS IN THE AIRFLOW !

After I built the Homemade HEPA filter, I was thinking of another idea that might work as well. A friend of mine wanted a filter setup that was portable. He has a glove box and that works well for smaller tasks but he would have to spray tons of disinfectant every time he opened the glove box. We got a small but very efficient room air filter that was made by 3M. This filter was self contained and had a fan that forced air through the filter. We took the outlet side of the filter and mounted it in a hole that we cut in the back of the glove box. We then sealed the gap between the box and the filter housing. This is a good set up because it is portable and can be stored. He still needs to use disinfectant but the amounts are considerably less that before. After we built the filter for the glove box I also thought that someone could build a large enough box and just have the filter and housing just sit in the box while you are doing the inoculations. This would work well because you are just having to filter the clean air the remains in the box

Some other Ideas for sterile work:

When you are doing inoculations using the filter, you want to have the area around the filter clean. This means that if you are doing the work in a basement you may want to seal the area off with a plastic drop cloth. This is also effective in reducing the rate of infection because many times the corner of the basement that you use has corners that are full of little nasties that would just love a meal of grain or agar. The Plastic will seal off the contaminates and prevent them from spreading to your work space. This will reduce the area that needs to be filtered and thus, reduce the contamination that will occur. Another idea would be to do inoculations in a small walk in closet or pantry.

Another idea that you may want to use is a 10% bleach-water solution in a cool mist humidifier. This is only good if you have a small area that you can do this in without concern for damage to the area (e.g. don't use this in your bedroom or everything that you own will be bleached and mom and dad will wonder why there is a bleach odor coming from your room, kick the door down and find out that you have a rather large pan of mushrooms growing and call the cops to incarcerate you for 5-10 years with good time off for good behavior and you will never be able to be a plumber because you are not allowed to hold a license of any kind because of the felony conviction prohibits you from attaining such a license.)(I guess Mario and Luigi never got busted for all those shrooms then!)

This is good because it is cheap and very effective. I was able to get a cool mist humidifier at a Thrift store for about $3.00 and I use it in addition to the filter setup that I have running.



By Joe Mamma (Madscientist) on Sunday, November 18, 2001 - 06:39 pm:

I will be building a flow hood soon. I would like to make a large one. Say 4x3'. I am using a fan removed from an air condition condensor. The kind that is used in a central air system, 5 ton. The coil makes for a great radiator in your terrarium. The fan is mounted in a box and is control by a fan/speed control. The only thing that sucks is that the HEPA filter cost around 300 beans. I was thinking that I could get away with a few layers of decent HVAC filters. I also would add a pre fan filter to extend the life of the multi layer filter. Anyone have any thoughts?

By Nan (Nanook) on Sunday, November 18, 2001 - 06:51 pm:

With the airflow you are describing you will need a HEPA filter for your final stage. HVAC filters alone (even with a prefilter) are not going to cut the mustard.

By plinkerdink420 (Plinkerdink420) on Sunday, November 18, 2001 - 06:54 pm:

oven is easier

By Joe Mamma (Madscientist) on Sunday, November 18, 2001 - 06:56 pm:

Do you know what makes up a HEPA filter? Is the spacing in the fiber what makes these things the best?

By Nan (Nanook) on Sunday, November 18, 2001 - 07:13 pm:

HEPA filters are engineered to trap 100% of small particles, spore sized particles. There is no substitute for a genuine HEPA filter where large amounts of airflow are present.

By George W. Bush (Xatomichristx) on Sunday, November 18, 2001 - 10:20 pm:

ok it's like this guys: hepa filters are designed to force the air to go through 90 degree passages, thus trapping a HUGE amount of particulates in the air passing through. HVAC filters simply trap particles of a certain size and let anything smaller go through.
HEPA filters are a necessity for CLEAN air.
The idea you're talking about might be ok for already established colonized cakes or whatnot, but for innoculation or things like that, you NEED hepa filters.

By Patrick (Valence) on Monday, November 19, 2001 - 12:34 am:

You can buy replacment Hepa filters for vacuums and air cleaner systems for pretty cheap. Use those with you own air system.

Posted by: Mycota Jan 19 03, 02:40 AM GMT
Mycota wink.gif

Posted by: slickstk187 Jan 19 03, 05:53 AM GMT
thanks. mycota
it's interesting to know exactly how easy it is for which fuckers to get into my shit. goood thing i don't smoke...


Posted by: DirtyWOP Jan 19 03, 10:06 AM GMT
Not ALL mold spores are 30 microns in length.....
I wonder how large different types of bacteria are???

Posted by: DirtyWOP Jan 19 03, 10:21 AM GMT
That got me thinkin'......
How is it I get bacteria spreading so much, if it doesn't have spores?
When I get these contams, am I introducing LIVE organisms to my growing medium?

heres a snippet from somewhere....
Reproduction in bacteria may occur asexually by a form of cell division called fission or sexually by a transfer of genetic material from a donor bacterium to a recipient.

check this out Mr. .3 micron HEPA filter

Common Name: Wet Spot
Microscopic Characteristics: 0.2 - 1.2 microns

Gee....I'm glad I got the 99.99% HEPA instead of the 99.97%
b/c apparantly
some wet spot cells can make it right thru....

Did you know that the most notable species in the genus BACILLUS is Bacillus anthracis..........any guesses what that is?

Ok apparant bacteria DO have endospores........thats what it said......
They say that in less than 14 hrs.....One TRILLION wet spot cells can reproduce from a SINGLE parent cell.....

ok time to shut up wop
go learn in the corner
and leave us alone

Posted by: sinoptik Jan 19 03, 11:41 AM GMT
No, continue on wop. I enjoy reading your posts about all the technicalities of fungi and bacteria. I wish I knew as much as you guys do but I'm sure time will tell once I read up enough on the subject.

Posted by: Fungusmaximus Jan 19 03, 04:21 PM GMT
I thought that wet spot bacteria needed an excess amount of moisture to infect the sub. No?

Posted by: DirtyWOP Jan 19 03, 04:41 PM GMT
I'm sure wet is the environment it any bacteria or fungi....
but it doesn't have to be overly wet to get contaminated.
Even when you got your moisture right in grain, you can most certainly still get wet spot.....

The bacteria actually makes the substrate look fact, let it sit for more than a day or two and it will completly LIQUIFY your substrate....
esp. whole grain rice

Posted by: repobob Jan 19 03, 05:04 PM GMT
I'm sure wet is the environment it any bacteria or fungi....
but it doesn't have to be overly wet to get contaminated.

Thats really interesting Wop. It explains a lot to me. I have had jars that had Wet Spot and your right the grain would turn into slop. I always thought this was to much water, but couldn't figure out why one jar in a batch would do it, but the rest were ok. The bacteria eats the grain and release the moisture in each grain which creates the slop.

One more reason for me to build a flow hood or glove box.

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