The level of ozone produced by too many of ionizers or free standing
electrostatic air "cleaners" causes lung damage -- and not only to
ferrets.

A place to start learning:
http://www.epa.gov/iaq/pubs/ozonegen.html

including:
>The same chemical properties that allow high concentrations of ozone
>to react with organic material outside the body give it the ability
>to react with similar organic material that makes up the body, and
>potentially cause harmful health consequences. When inhaled, ozone
>can damage the lungs (see - "Ozone and Your Health" -
>www.epa.gov/airnow/brochure.html) . Relatively low amounts can cause
>chest pain, coughing, shortness of breath, and, throat irritation.
>Ozone may also worsen chronic respiratory diseases such as asthma and
>compromise the ability of the body to fight respiratory infections.
>People vary widely in their susceptibility to ozone. Healthy people,
>as well as those with respiratory difficulty, can experience breathing
>problems when exposed to ozone. Exercise during exposure to ozone
>causes a greater amount of ozone to be inhaled, and increases the risk
>of harmful respiratory effects. Recovery from the harmful effects can
>occur following short-term exposure to low levels of ozone, but health
>effects may become more damaging and recovery less certain at higher
>levels or from longer exposures (US EPA, 1996a, 1996b).
 ...
>Manufacturers and vendors of ozone devices often use misleading
>terms to describe ozone. Terms such as "energized oxygen" or "pure
>air" suggest that ozone is a healthy kind of oxygen. Ozone is a toxic
>gas with vastly different chemical and toxicological properties from
>oxygen. Several federal agencies have established health standards or
>recommendations to limit human exposure to ozone. These exposure
>limits are summarized in Table 1.

Go to the URL to read that table.
...
>Ozone has been extensively used for water purification, but ozone
>chemistry in water is not the same as ozone chemistry in air. High
>concentrations of ozone in air, when people are not present, are
>sometimes used to help decontaminate an unoccupied space from certain
>chemical or biological contaminants or odors (e.g., fire restoration).
>However, little is known about the chemical by- products left behind
>by these processes (Dunston and Spivak, 1997). While high
>concentrations of ozone in air may sometimes be appropriate in these
>circumstances, conditions should be sufficiently controlled to insure
>that no person or pet becomes exposed. Ozone can adversely affect
>indoor plants, and damage materials such as rubber, electrical wire
>coatings, and fabrics and art work containing susceptible dyes and
>pigments (U.S. EPA, 1996a).
etc.

My father in law's pulmonologist and my allergist recommend hepa filter
air "cleaners" when people want to filter air.

With humidifiers be sure to clean them often; they easily grown certain
molds and algae, possibly also cyanobacter.

Some resources also mention cleaning problems caused by ionizers; I
know squat about that so you'll need to use a general search engine
like google.com and look that up.

Sukie (not a vet)

Recommended ferret health links:
http://pets.groups.yahoo.com/group/ferrethealth/
http://ferrethealth.org/archive/
http://www.afip.org/ferrets/index.html
http://www.miamiferret.org/fhc/
http://www.ferretcongress.org/
http://www.trifl.org/index.shtml
http://homepage.mac.com/sukie/sukiesferretlinks.html

[Posted in FML 6000]