I inspected a one year old condo yesterday that had an interesting installation.

It seems the dryer vent just exhausted into the attic at first. The builder then extended it to the outside. It goes up 10' or so then turns and runs another 20 feet or so. That didn't work so well, so they installed a dryer booster fan.

There's only a couple things wrong with that installation:
1. They attached the bracket to the roof truss - OK so far.
2. But failed to attach the fan to the bracket. It was close, only about an inch away.
3. They wired it to the forced air unit in the attic. They actually wired it to the "other" side of the switch, so if you trun off the switch to service the forced air unit, it will cut ff power to the fan.
4. The forced air unit is on it's own 15 amp/120V breaker.
5. One last thing - The fan doesn't work even though it has power going to it.

Got to love it
JF