First of two posts I found in my files - hope they help:
    Hi Lin:

    Humidifiers work, but again, they are the lowest quality.  People think 
that a big, thick mist that nearly chokes you when you breathe it in indicates 
a high quality and a high level of effectiveness...  In truth, the exact 
opposite is true.

    As an example, the "Brooks Bradley" oxygen nebulizer, when used most 
effectively, has a mist so fine that you cannot even see it without using a 
mirror ( using the CS nebulizer to fog the mirror ).

    The highest quality ultrasonic nebulizers create a very fine mist that 
actually has quite a dry feeling when used.  The fine mist medical nebulizers 
create "vaporized particles" that more easily penetrate deeply.

    Furthermore, Stephen Quinto, years and years and years ago, studied the 
effective difference between different types of atomizing technologies on 
colloidal silver.  All of the mechanical technologies, including pressure-fed, 
adversely effected the quality of the colloidal silver used ( in other words, 
every other type of nebulizing technology other than ultrasonic ).  How much 
the change interfered with the actual effectiveness of the silver in-body, of 
course, could not be determined... if it does at all.  
  Never-the-less, I don't want such simple truths to be lost.

    Humidifiers, even ultrasonic ones, are designed with dispersion in mind, 
not vapor atomization ie. vapor particle sizing.  For pets, due to logistics, 
it MIGHT be a better choice to use one, as it can be troublesome to get a pet 
to sit still and breathe in the fine mist from a nebulizer... but for people, 
the high quality technologies are vastly superior.  I've tested medical oxygen 
nebulizers, the "Brooks Bradley" oxygen nebulizer ( my personal favorite ), 
pneumatic nebulizers, ultrasonic nebulisers, and 
  humidifiers.

    I usually use a Omron ultrasonic nebulizer, as it is the most convenient 
and quite effective.  Nebulizing EIS, this flu season and last, seems to be far 
more effective than oral use alone.  The flu strains running around the cities 
this year are particularly brutal.  

    Yes, there is alot of different information out there, which can be very 
frustrating, considering that we're dealing with a science here and not an art.

    I don't know about 24 hours a day...  Five minutes every hour or so would 
be wonderful, but you'd have to get the cats to directly inhale the CS from a 
nebulizer or humidifier.  If you are considering using a humidifier to lob mist 
into the "general vacinity" of the animals, then I'm not sure how to advise... 
as you can't really be sure that the cats are actually breathing in any silver. 
 You'd have to experiment and actually examine the environment to see if you 
can tell if you are successfully reaching the 
  cats.

    Best Regards,

    Jason