The Fantech rep is in the business of selling fans. While I love their product line and it's the one I prefer to install, for inside a steam shower you'd want a sealed unit with a positive closing damper.
The "sealed" aspect will keep steam vapor from penetrating into the guts of the fan. The closing damper will prevent vapor from being driven into the duct work, where it will cool, condense, and drip back down into the fan housing, or into the shower through the fan's grill.
Don't confuse the little gravity flapping backdraft damper on most fans with a "positive closing" damper.
The positive closing dampers can either be motorized or spring loaded, gasketing can help provide a positive seal.
Q
