In-Line Duct Fans - Are These Noisy?

They can be noisy. I had a new house built and the HVAC people were incompitent. The upstairs was cold in winter and hot in summer. Long story short, fans had to be put in-line to get the air upstairs.
When the fans were first installed, it sounded like a jet taking off. The people that put them in (different HVAC company) came back and put rheostats on them to slow them down. Now they are hardly noticable. The air level can also be adjusted if you need more cold in summer or warmer in the winter.
Overall, they have worked great for our application. Sorry for the long post, but if you have any other questions, let me know.

I think you may have to look a bit harder to find ones that are less noisy. Kind of like the bathroom fans - the cheaper ones are more noisy and you go from there...

Not all in-line fans are the same. Are you talking about the kind with a centrifugal blower? There is a lot of mass to the fan so mounting it in such a way as not to send vibrations through the structure is really important. I have mine sitting on rubber isolation mounts directly on the concrete floor and it has a rag coupling to isolate it from the duct. I built a heavy 25"x48"x16" box out of 3/4" OSB to house it and two furnace filters. I created a labyrinth for the airflow to reduce sound transmission through the duct but I need to open it up and line the interior with rigid fiberglass insulation for better sound absorption. It is quieter than the furnace blower but the fact it is running all the time, I want to make it quieter yet. I also read that there is a better Lutron speed controller that reduces hum and am on the hunt for one now.

I move cold air with it to the stove.

I added one of these in duct style to a vent right over the stove to get air into a bedroom above the family room. Would say the fan is noisy but I can not hear it over the stove blower so its not an issue. No vibration issues as I used the insulated flex duct instead of metal so I have to say I like it. Did use a dimmer switch on this so I can turn it down when its 30+ out and max it out when its below 20. I move heat to the bedroom instead of cold to the stove as I tried it both ways extensively and found this to work best in my application. I do also have a twin fan vent register set up in the hall way on my 2nd floor other end of the stove room and sure its got some noise but is a 3 speed so I can turn it down. However as this one sits next to a humidifer hearing it over the register fans is the problem, but part of the game.

Just put in a Fantech 6XL which draws air through my existing furnace ductwork, and outputs into the room with the stove. Right now I have it mounted on a piece of plywood which is directly attached to the floor joists.

The noise from air passing through the venting system isn't bad, but I'm drawing from the whole house, not from a single vent (someone let me know if I'm breaking code with this...I couldn't find anything with a quick search). I did have it on a single register with metal ductwork at first, and the thing was like a jet-engine... unacceptable according to the wife! With flexduct, the noise was very much reduced, but still a bit too loud.

The only noise issue now is the mechanical coupling through the joists. It's not a huge issue for me, but it definitely didn't go away with adding a rheostat...it actually got worse (just like a ceiling fan sometimes makes more noise on low speed, the motor vibration was worse at low power). At some point I'll do my best to decouple the fan from the floor...perhaps a suspension mechanism would be better.

It has been reported that the Lutron FSQ series 3 speed controller may be quieter than the variable speed controller. I have one on order.

I think elicient (sp) is on of the top in-line fans... there are a few brands... all you can hear is the wind moving, and they are sealed and very well designed and long-lived... used in greenhouses and growrooms. See the web. 150$-500$ I would guess, go from I believe 4 to 12 inches. I would say a six would be ideal ....

anka

anka said:

I think elicient (sp) is on of the top in-line fans... there are a few brands... all you can hear is the wind moving, and they are sealed and very well designed and long-lived... used in greenhouses and growrooms. See the web. 150$-500$ I would guess, go from I believe 4 to 12 inches. I would say a six would be ideal ....

anka

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jets are ducted fans! they are noisy

I just installed a 6 inch Aero Flo brand off ebay for $35. It's working well and is rated up to 270 degrees for those of us using it to move air from above the stove. I'm happy with it.

Hi;
I got help through another thread on this same issue.
In the end, I have a Fantech FG4 in-line centifugal fan, with a Lutron 3 speed controller (from Home Depot).
The Lutron controller works much better than the simple rheostats I tried earlier. I do not understand the electronics, but with simple rheostats I got an annoying hum, and I could not tune it out.
With the Lutron 3 speed, there is no hum.
The Fantech FG4 itself is almost silent. I mounted it on stiff neoprene pads. But my duct system has some air-movement noise; that would depend on the installation, I think.