We have a booster fan built-in to a 8 inch round duct. This was
needed for the long run, 50+ foot. It has a rheostat for speed
adjustment. Seems to move the air just fine at 60% of full
power. Problem is the noise. When the air is moving the noise
travels to all the rooms. We did replace it, thinking the first
one was defected. Does anyone know of a quiet booster fan?
I wanted to add that locating the duct fan well away from the supply and
close to the destination would reduce the noise to other areas other than
the one being served by that specific duct.
I will also add that if there is any other solution, like a better or
larger duct or improved duct distribution design and the elimination of the
fan, that may be the best method.
I'll add my own experiance with this sort of thing.
There are two sources of noise; fan motor noise, and the noise of the
air being moved through the duct. We put in the 8 inch version of this
fan to warm up a bedroom at the recommendation of the local HVAC
The first thing I discovered is that it moves _WAY_ too much air. (It's
nearly half the CFM of the blower fan in the furnace that supplies the
entire house.) In addition to moving way too much air, it was noisier
than heck. So next I went to the electrical supply place and got the
recommended motor speed control for this fan and installed it. I was
then able to dial down the fan speed to reduce the CFM. At that point,
I discovered two more things; that at the minimum setting that the
motor would still run, it was still way too much air movement, and also
I learned that motor noise _increases_ as you decrease the fan speed.
So the air movement noise was lower, but the fan motor noise was
higher, and together it was still too much noise, and it still moved
too much air. So next I started backing down the damper in the duct.
We now have the damper nearly shut off completely, the fan runs at the
lowest speed that I can stand the fan motor noise, and it still moves
too much air, and it is still too noisey, to the point where we shut
the fan off during the daytime because of the noise and only use it at
night when my son is sleeping in the bedroom and the room needs to be
My conclusion from all of this is what everyone else already knows,
that it is far better to solve the original problem for why the room in
question is too cold. The in-line fan solution is only a band-aid, and
not a very good band-aid. I've tried doing a bit of research on the
matter, but there seems to be little information from many of the
manufacturers. The last I looked a couple years ago, there were
numerous in-line duct booster fans on the market, but most many sellers
of these devices don't even list how many CFM the fan moves, or any
sort of sound rating.
Sorry I'm not much help other than to say that in my experience, you're
kind of stuck.
A muffin fan is the way to go. We have a food dryer that had a 4 bladed fan
and was very noisy. I replaced with a muffin fan of same physical size. Has
same airflow and so quiet can't tell if it is running without feeling air
flow. W W
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