Wednesday, January 8, 2014

Add HEPA filtration to any CPAP for $20

In a previous post I had written about my attempts to modify the Resmed S8 to add HEPA filtration.  The purpose was to help my allergies and asthma, and maybe by reducing my allergen load I might even improve the quality of rest I get when I sleep.   I've also written how dissapointed I've been in that Resmed and other's don't offer this as a standard feature, and that the filters they DO offer are so chintzy.  Those little inserts are designed to protect the CPAP, not you.

In the past I had thought of elaborate schemes to do this, going so far as to order industrial HEPA medium (i.e. filter) for the woodworking industry, cutting it to fit, I've thought about making special molds or filter holders to fit the wonky air entrance of the S8, making a custom CPAP filter box, you name it.  All those solutions were expensive, time consuming and most looked ugly.   I have finally found a good compromise which is ridiculously easy to make, very inexpensive and at least after my first night, worked flawlessly.

You'll see a picture of my prototype below.

You will need the following supplies:
  • A CPAP machine, such as the S8, but almost any will do. 
  • Wide tape, such as packing, duct or Gorilla.  
  • Kenmore Q Vacbag Style Q
  • Scissors
The idea is simple.  The Kenmore Q bags filter down to the same size of particles as HEPA requires.  This is very good for anything short of laboratory grade clean room filtration. 


Because some packing tape can off-gas it's a good idea to do this several hours before you go to sleep. 
  1. Cut the bag open at one side or the back.  Just enough to allow you to slip your existing CPAP machine into the bag. 
  2. Detach the hose and thread it through the intake of the bag.  Then attach it to y our CPAP.  
  3. Remove any existing air intake filters.   
  4. Put CPAP in bag, pulling out as much of the air hose as needed to snugly fit the bag's opening up to the CPAP itself. 
  5. Make sure the power cord is attached.  It's probably easiest to move it to one side or the other of the slot you cut. 
  6. Close the slot you cut out with the tape.  Try to get as air-tight a fit as you can. 
  7. Check that the CPAP air intake is not pressed up to the media.  You want to have that be loose fitting, with room so that as much of the bag's surface area is used as possible.   
  8. Optionally, tape the hole around the hose itself, where the bag's cardboard insert is closed.  
For best results, keep the bag as loose as possible so there are as many paths of air available.

Congratulations, you now have a very efficient,  and inexpensive, HEPA filtration system attached to your CPAP machine.  May you have many allergen free nights of rest. 


In terms of efficiency, etc. the bag is incredibly well suited to this task.  Though the filter is of a much tighter weave than the OEM part we compensate for this by having about 100x or more surface area.

You should notice is that the bag does not crumple when you turn the CPAP on.  In fact, the bag doesn't do anything.  This is a VERY good sign that the bag is barely in the way of the airflow.   Imagine for instance if the bag were a trash bag instead.  Because the bag has no air flow, as soon as you turn the CPAP on the bag would collapse, like a vacuum seal food infomercial.   The same is true by the way in the woodworking / industrial application of the media.  If the media inflates very firmly it means it's clogged up and restricting airflow.

Isn't this like perpetual motion? 

No, not really.  We are taking advantage of the fact that while the bag is good for a vacuum cleaner it is overkill for our needs.  Think about how much air a vacuum has to suck per second, versus how much air you can intake in a second.  No comparison.  The bag is designed for much higher air flow than the CPAP could possibly need but has much better filtration than CPAP vendors offer.   The vacuum bag will not only will keep dust, dust mites, molds, etc. from the air you breathe, but will reduce the power consumed by the CPAP and ensure that enough air flows around the unit naturally to keep the machine at normal operating temperatures.  All in all, a win win for you, the CPAP and the environment. :) 

Is this worth doing?

Maybe.  We do know that allergies, like colds, activate our auto-immune system which takes energy and stresses our bodies so the idea that reducing allergic response could lead to more energy and less stress is completely medically and scientifically sound.   I also believe that the bags filter many more allergens from the air than the S8 foamy filters can.  However, whether adding a HEPA bag to your CPAP will make a difference to your situation may require experimentation but at $20 per experiment I think it's worth trying.  

Here's my suggestion, if you know you suffer from allergies, and you are condemned to a life of sleeping with CPAP, try it for a week.  See how you feel and how alert it makes you.  Blog your experience either way.