knobbies on my furnace duct work??

[WoodButcher80]

hey guys.

attached is a picture of my furnace duct work. you can see the edge of my oil furnace to the right. well, youll notice 2 white knobs with coiled electrical wires attached to them. they turn one full rotation. if i turn them to the left all the way, they will click and shut off. if i tun them a millimeter clockwise the fan inside it controls will be on high, and then it fades when i go more clockwise to the fan being low. both round ducts have them .... why would i want them fast or slow? is this some type of damper to control how much air i want through each duct to different rooms ? thanks

(CLICK ON PIC TO MAKE BIGGER)

 

[Hogwildz]

I am guessing they are in line fans. The controls are similar to dimmers, as in they control the amount of current delivered to the fans.
You adjust the fan speed to desired amount of cfm you want each fan to blow. Basically booster fans.
They could also be dampers, but dampers do not have fans, so that pretty much rules that out.

 

[WoodButcher80]

im sure theyre fans. . . guess i need to just figure out where they go now! thanks for the help.

 

[Hogwildz]

Are they blowing from one plenum to another?
Kinda strange set up.

 

[WoodButcher80]

heres more pics i just took for you to figure it out

well i know theyre not exhaust ducts going into the concrete cus the chimney flue exhaust duct is in the last picture in the far far corner on right.

the pipes in the concrete are going towards my the floor of my family room, which is on a slab.

 

[Highbeam]

Booster fans. Someone thought that the ducts weren't passing enough hot air to the vents on that run so they kicked it up a notch with the fans. They may be wired to only come on when the furnace runs or they may be constantly on. If you shut them off then they will obstruct the duct slightly.

 

[Hogwildz]

heres more pics i just took for you to figure it out

well i know theyre not exhaust ducts going into the concrete cus the chimney flue exhaust duct is in the last picture in the far far corner on right.

the pipes in the concrete are going towards my the floor of my family room, which is on a slab.

If the slab has registers in it, then thats exactly what those pipe runs are for.
HB is right, the fans if off when the system is running, may cause some drag. Although they may also spin a lil from the pressure if great enough.
But I am thinking that would be pressure wasted to getting it tot the registers.