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Old 02-28-2020, 03:51 PM   #1
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Duct booster fan, noisy? Useful?


Hi everyone,

I live in an old house (over 100 years old), with a new furnace and old ducts.
Essentially I have one bedroom and one bathroom at the back of the house that feed from the same duct and are not getting a lot of airflow. Those rooms are significantly cooler than the rest of the house in the winter (I live in Canada, temperatures can get fairly low during winter).

I asked an HVAC professional to come and take a look and his conclusion was that there's really nothing easy to do because the duct feeding that bedroom has a lot of 90 degree angles (to go around a joist) and is undersized (6"). His recommendation (of course he recommended fixing the whole system first) is to install a booster fan in the basement, just before the duct disappears into the ceiling. I perfectly understand that a booster fan is not the ideal solution but at this point in time, I have little interest in opening my walls to fix the duct work, as this would be a massive undertaking and the house was renovated less than 10 years ago (you'd think the previous owners would have updated the ducts at the same time..).

Anyways, what's your opinion? Can a booster fan push that air up to my second floor (straight duct coming from the basement)?

Will it be noisy? In the bedroom? In the family room near the mechanical room? On the main floor?

I've never seen one of those installed, so I have a hard time gauging their efficiency, and the risk of hating the extra noise.

Do you have any advice I could use?
Thanks!

Florent
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Old 02-28-2020, 04:12 PM   #2
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Re: Duct booster fan, noisy? Useful?


You can try but they don't have a good reputation.

if your trunk line feeding that side of the house is undersized, it would steal air from other rooms at best.

Need a centrifugal version which can move decent amount of air under high pressure.

the only real fix is adding a second run.
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I am not in the business of any trade I give advice on. I have non-professional hvac experience + good knowledge of theory. Attempt repairs at your own risk. Never jump out safeties - especially pressure switches - on a furnace for testing with fuel supply on; use a meter. Do not troubleshoot with live line voltage present unless there's no alternative.
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Old 02-28-2020, 06:15 PM   #3
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Re: Duct booster fan, noisy? Useful?


Duct booster fans help but the downside is noise. Not only will the fan make noise, but increasing airspeed in the duct can cause noise. I would use a supplemental electric heater for the extreme cold days.
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Old 03-05-2020, 09:19 AM   #4
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Re: Duct booster fan, noisy? Useful?


@user_12345a
Directly above my furnace is a big metal 'box' that branches out into smaller ducts. One side of my house (with good air flow) is feb by two large square ducts. On the other side, there are two smaller 6" round pipes also coming out of the box. One essentially goes straight up to a small bedroom (air flow is fine) and one has a lot of 90 degree angles and feeds a bedroom and a bathroom at the back of the house (the ones with low air flow).
Do you think that would steal a lot of air from the other rooms?
@Old Thomas
Thanks for the tip, I am also considering that option. The only problem with it is that it doesn't help with air conditioning in the summer. At time, I guess I just have a hard time gauging what the noise/air flow impact would be, so I can make the right trade off for my situation.
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Old 03-05-2020, 11:51 AM   #5
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Re: Duct booster fan, noisy? Useful?


Quote:
Do you think that would steal a lot of air from the other rooms?
It would but at least it would be balanced, not just taking from the back

The duct setup you described is bad, they should have used trunk line and definitely never should have split a single 6" between rooms.

I doubt a duct booster will fix distribution, the single 6" is probably undersized for both rooms especially given it has lots of elbows.
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Old 03-05-2020, 04:58 PM   #6
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Re: Duct booster fan, noisy? Useful?


I use these in my house. I tried all the duct booster fans and none of them worked as well as these. Get the speed adjuster so you can turn it down or up some. They are quiet except for the air rushing. I cut out a section of the metal duct, attached a small piece of flex duct on each side of the fan and hung it up by rubber bungie cords so it's suspended and not touching anything to make a vibrating noise. Love them.

https://www.amazon.com/Hydrofarm-ACD...X40G64WTX7J3ZS
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Old 03-05-2020, 05:37 PM   #7
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Re: Duct booster fan, noisy? Useful?


I've had very little experience with the duct fans, so I cant really provide any feed back on them, but I agree with the supply trunk being terribly undersized. However, you might take a look at the Return air from the cold rooms. if there is insufficient cold air return, the hot air supply will be reduced accordingly. you might experiment by using a box fan to SLOWLY pull the cold air out of those rooms, and see if that identified a possible solution of increasing the return air flow.
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Old 03-05-2020, 06:03 PM   #8
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Re: Duct booster fan, noisy? Useful?


Quote:
Originally Posted by taylorjm View Post
I use these in my house. I tried all the duct booster fans and none of them worked as well as these. Get the speed adjuster so you can turn it down or up some. They are quiet except for the air rushing. I cut out a section of the metal duct, attached a small piece of flex duct on each side of the fan and hung it up by rubber bungie cords so it's suspended and not touching anything to make a vibrating noise. Love them.

https://www.amazon.com/Hydrofarm-ACD...X40G64WTX7J3ZS
yah that's the only type that could do anything.

the cheap ones with axial/propeller type fans look useless.
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Old 03-06-2020, 02:21 PM   #9
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Re: Duct booster fan, noisy? Useful?


First of all, thanks everyone for sharing your thoughts, that's really helpful.

Quote:
Originally Posted by Stanlysteamer10 View Post
I've had very little experience with the duct fans, so I cant really provide any feed back on them, but I agree with the supply trunk being terribly undersized. However, you might take a look at the Return air from the cold rooms. if there is insufficient cold air return, the hot air supply will be reduced accordingly. you might experiment by using a box fan to SLOWLY pull the cold air out of those rooms, and see if that identified a possible solution of increasing the return air flow.
I like the idea! I have two returns on this floor, that are on top of each other (one closer to the floor, one closer to the ceiling, not sure why..) but they are closer to the rooms that are warmer. I want to give this a try.

Now, just out of curiosity. If I found out that it was the problem, what would my options be then?


Quote:
Originally Posted by user_12345a View Post
yah that's the only type that could do anything.

the cheap ones with axial/propeller type fans look useless.
The contractor who suggested I install a fan is suggesting the VTX400. This one is 4" (my pipes are 6") but apparently it has an integrated pressure switch that makes it easier and less expensive to install.
Any thoughts on that model?
What about the sizing of the fan? I'm a bit skeptical about the downsizing, wouldn't that add even more resistance to the air? I saw videos online of people controlling the fan with a temperature sensor, didn't seem that hard to install. Is that a common practice?
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Old 03-06-2020, 02:29 PM   #10
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Re: Duct booster fan, noisy? Useful?


Quote:
Originally Posted by flofloflo View Post
Any thoughts on that model?
What about the sizing of the fan? I'm a bit skeptical about the downsizing, wouldn't that add even more resistance to the air? I saw videos online of people controlling the fan with a temperature sensor, didn't seem that hard to install. Is that a common practice?
That model is actually made for a dryer vent, that's why it comes in 4". It's also quite expensive. It comes with a pressure switch that will activate when the pressure in the duct increases when the furnace blower turns on. Of course, I don't quite understand what happens when the fan activates, and the pressure decreases. Seems like the fan would cycle on and off. Plus it only offers about 200cfm verses the one I'm using with is over 400cfm. I'd much rather have too much, and use the speed controller to turn it down some then to not have enough. I wired mine to run with the furnace blower. Most furnace control boards have a switched 120v connection.

Last edited by taylorjm; 03-06-2020 at 02:38 PM.
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