Hi Ralph,
Thank you for contacting Desert Spring Products. I am not sure what kind of
experience this installer has had, but this is an opinion not based on fact.
He may have a valid concern if you were considering a misting or steam
system, which are 'active' humidifiers. This means they can force vapor into
the air stream which can condense out if the air is close to dew point. A
by-pass system is completely passive, which means the humidifier's vapor
will only be picked up if the air can accept the vapor. Furthermore, the air
path going through the furnace and filter is never in contact with the
furnace control board, this is safely mounted outside the air stream, so
this is complete nonsense.
Thank you,
Peter