in-line duct fans

[electron]

Has anyone ever installed one of these? I noticed Home Depot carries the exact same models SmartHome.com does. I did notice that the 8" moves 500CFM of air, while the 6" is 250CFM (I have 6" ducts), kind of disappointing that the CFM rating drop is that big.

I was planning on installing one of these just to see if it will make things cool down faster, so hopefully someone can share their experience regarding install/performance before I waste money on something that might not work.

 

[MeSteve]

The house I gerw up in had one duct run that was really long so that corner of the room was always cooler than the rest of it. My dad installed a squirrel cage fan and that made all the difference. Not sure how it relates to your question, just throwing 2 cents.

 

[elcano]

I did notice that the 8" moves 500CFM of air, while the 6" is 250CFM (I have 6" ducts), kind of disappointing that the CFM rating drop is that big.

The cross-sectional areal of the 6" fan is about 56% of the 8" fan. This is the reason. It doesnt look like that much, I know.

 

[electron]

interesting ... I guess I will just have to get one and give it a shot, since so far no one seems to have tried one of these.

 

[jasv]

I tried a couple of them. It didn't really make much of a difference for me.

 

[ellisr63]

how do these work compared to the bathroom type ventilation fans? Are they noiseier, more flow....

 

[Guy Lavoie]

To really work, an inline fan would need to be as close as to the main trunkline as possible. The extra air that its attempting to push down the feeder duct has to come from somewhere, and the main trunk line is its source. If its too far down the feeder, it will just create a slightly higher vacuum behind it because of the duct friction. Fans suck at sucking...

 

[electron]

I tried a couple of them. It didn't really make much of a difference for me.

Welcome to CT!

What size fan did you go with?

 

[Rupp]

Dan,
I have 2 of these 6" inline fans. I too didn't see much benefit from them. I ended up running a new ducts to the "hot" part of the room which dramatically made a change. YMMV.

 

[pete]

I did notice that the 8" moves 500CFM of air, while the 6" is 250CFM (I have 6" ducts), kind of disappointing that the CFM rating drop is that big.

250 cfm in a 6" round duct is going to be noisy, air is moving around 1400fpm . . . usually don't want to go over 800fpm or so . . .

. . . that is if the fan delivers 250cfm when actually connected to a long run of duct . . . performance drops the longer, and more bends the duct run has . . . and often those in-line, propeller type fans' performance is stated with no duct attached . . .

but it may be worth a try . . . save your receipt and you can always just put a short section of 6"rd duct back if you aren't happy with it . . .

Pete C

 

[electron]

Dan,
I have 2 of these 6" inline fans. I too didn't see much benefit from them. I ended up running a new ducts to the "hot" part of the room which dramatically made a change. YMMV.

That actually sounds like a good idea. I have one wall which has no registers at all, and the wall is within feet from the main duct below it, so it would be a really short run. My only concern would be that the other registers would be even less efficient now, since I assume the HVAC system planned with X registers in mind.

 

[pete]

since I assume the HVAC system planned with X registers in mind.

well, CFM actually, you get 400cfm per ton (12,000 BTU) of A/C . . . this is adjustable to a small degree as most air handlers have a jumper that lets you tweak the fan speed (down to about 360cfm/ton). . .

I would try the additional branch run/register before adding any booster fans . . . use a branch collar w/ a volume damper (into the existing duct) so you can adjust the flow to the new outlet . . .



Pete C

 

[electron]

I guess I will have to check out how hard it would be to connect that branch to the main run, since I am assuming I have to do some cutting.

 

[pete]

a hammer, large, straight screwdriver and a decent pair of snips and your in . . .

Pete C