How to make an inexpensive HEPA filter

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This article will show you how to make your own DIY HEPA filter for cleaning the air inside of your home.  It is important when removing mold, that you ensure that the spores that are released during those efforts do not distribute into other areas which could cause a problem.  HEPA filtration is what is used to catch errant spores that are released in the air.  A good commercial HEPA filter costs upwards of $1,200 dollars and the filter cartridges are about $250 each give or take a bit.  As well the “pre-filters” used are expensive.  So, they are impractical for use in typical clean up activities by a homeowner.  You can’t really rent them either.  So what do you do?

This article The intention of this filter is for any temporary clean up projects.  For the purpose of ensuring that you do not make a small problem worse, this will do the trick.

Ok, so what does HEPA mean anyhow?

HEPA stand for: “High-Efficiency-Particulate-arresting”  Meaning that a HEPA filter has holes in the filter that are large enough to allow air to pass, but small enough to catch 99,8% of all spores and contaminants and trap them.  Think of a screen door.  If the holes were too big insects would get into your home.  If the holes were too small, you wouldn’t be able to see through the screen which would defeat its purpose.  So, the openings are sized correctly for its purpose.  The same with a HEPA filter.[/two-thirds] [/columns_container]

Here is what you need to make a great DIY HEPA filter.

a typical box type fan.  A HEPA rated allergen return filter (any brand will do as long as it is allergen/or HEPA rated.  There are designations MERV ‘XX’ you may see.  Try to get a MERV 13 or higher.  The filter only needs to be large enough to cover the exhaust portion of the fan (or use 2 of them).  You can use a bigger one and cut it.  Doesn’t matter.  The important part is covering the exhaust entirely and taping that seal to the outside of the exhaust.  The last ingredient is Duct tape (no not Duck tape; but Gorilla tape works great.

  1. fit the filter(s) to the exhaust side of the fan.
  2. Tape the filters to the outside of the fan ensuring that the air that passes from the fan, is covered by the filters.  Meaning when you tape over the edges of the filter to the fan, there is no air allowed to escape from the fan that isn’t going through the filter first.
  3. place the fan ideally adjacent to where you are working and if you can, at an open window or door such that the air flow is facing OUT of the home.  if you want to be creative, you can even attach a small piece of 10 or 12″ duct material to the exhaust and then simply run that outside. Remember the air that comes OUT of the fan will be filtered, but if you create air flow drawing air from inside of the home TO the outside of the home, you have created a bit of negative pressure.  This is good because then any spores that are aerosolized during the work, will be naturally drawn into the filter and out of the home.  This will also create a stronger attraction so to say to the intake portion of the filter itself. Its complicated physics, but it works.
  4. Turn it on and viola!  A great commercial grade HEPA filter.


After you have used the homemade HEPA filter and when you turn it off, take it outside immediately, remove the filters from the rear of the fan and discard them.

A word about containment or separating the “work area”

it is important that (even for the smallest mold project) that you separate the work area. This is an entire separate topic which I will publish something on soon.  However the basic principle is to separate off the air space in the area you are working.  You can use plastic, tape closed a door whatever.  There are many methods.  The best way is to seal off the area in plastic (sort of an isolation room if you will), then buy a zip closure from your local hardware store (about $9 dollars or so) and create your entry and exit to that isolation area.  With your homemade HEPA filter running, if you can, direct the air flow out of that work area to the outside.  Viola, now you have your own containment area and negative pressure environment to work in.  More physics.. But it works.

You now have a very effective commercial grade HEPA filter for your clean up projects for under $60 dollars!  Renting a commercial one is over $60 dollars per day!