Too Large of Inline Fan

You should be able to use a plug-in speed controller from some place like Radio Shack, etc. (Usual disclaimer). I'm no expert, but someone here will give you good advice.

A fan controller could be used. Two alternatives come to mind.

One is an adjustable louver at the exhaust end of the 'pipe'. (There is also magnetic sheet material that can be used over an existing steel exhaust vent to block some of the air flow, if a louver can't be used.)

The other idea is to install a Y coupling downstream of the fan and direct some of the air to another location.

I'm not sure why the existing rheostat wouldn't have a large enough resistance to slow the fan to near zero, but I imagine that you could add a further resistance in series (making sure it can handle the wattage.) Not enough numbers are present to assist with calculation. If the fan is hard to access, maybe the circuitry is easier.

To progress this idea of yours a bit further, a single diode, with a reasonable current and voltage capacity will effectively halve the voltage and should put the fan at about half of its slowest speed now, aproximately...

You may even need to turn the pot up slightly just to make sure it "self starts" each and every time....

try it out, its cheap and simple.

If you ever need the full speed again, just place a switch across the diode and switch it on to take the diode out of the circuit....

If this fan is so difficult to get at, what will you ever do if it fails? Because at some point it will.......maybe 10 years down the road.....

In domestic ceiling type fans when the fan regulators are not functioning properly we replaces the capacitor and it works. There may be some emf induction . Check the control wiring.

What about adding an ambient air bleed to the input (low pressure side of the fan) duct with an adjustable louvre if you want to lower the temperature further,

OR

If you want to reduce the flow at the current temperature you could add an in line louvre before your fan to restrict the airflow.

I would be cautious about trying to slow the fan motor down as many of the small motors greatly loose power & this causes high current draw & can over heat them quickly & even start fires at the motor, I have seen this happen with exhaust fans & even had to help put out the fire caused by a fan in the cieling of a house.

If you have to slow the fan use an electronic motor controler with current control incorporated, but I would be more inclined to do as sugested by Usbport & install a T after the out put of the fan and redirect some of the air, even if it is straight back to the room it comes from, controled with a damper like they use in ducted air con.

Even a basic flat slide over a hole in the side of a straight section of duct would be sufficient to redirect some flow Basically just vent the air to any other location to get the desired flow upstairs

oooops I forgot to sign in when I made the post above sorry

Which model Fantech do you have? From what I looked into, I will take a guess you have the 115V permanent split capacitor type motor. Looking at the flow chart, min CFM is around 900. If this is correct, it is possible that it can not run slower than this due to it's design. It does have class F insulation. I may over heat if run slower.

It does have an auto thermal reset so you cold try using a variable speed plug in unit. I have one for my router and works great. You could give it a try. They sell for around $20.00. It may have to be rewired into your control circuit.

Then run faster!!!! Cooling wind?

Sure you can it's called a damper . Install a damper to restrict the upstream side of the fan. You can reduce the size of the ductwork but thats more work then just adding a damper. They even make dampers that you drill a hole in the duct then slide the colapsed damper through the hole and then it opens up. We have used them before and they work ok. But a single blade damper works best. You can pick those up as most hardward stores.

At least half of these posts recommend restricting inlet or outlet to slow airflow. Your fan is over sized. Get the correct one. It will be quieter, more efficient, and not overheat because you are supplying incorrect current.

Post 11 called for a damper- good choice, but better if installed on the inlet side.

MUCH better choice is to replace the fan motor with one rated for slower speed- 1750 RPM to 1140 RPM or equivalent. The motor will be relatively inexpensive, only draw the power required (rather than burning it up with unnecessary load (damper) or through the reostat) and will produce 2/3 of the air volume that the original fan is (trying) to produce.

If you still get too much air, the damper will be the easiest to achieve your goal (and the least expensive- first and on-going cost.

Hi all: I called where I bought the fan and dug out the invoice. Here is what I have, Fantech FG Series Fan Model FG12XL Inline Centrifugal Fans Air Tight Steel housing For 12" found Duct - 940 cfm. Accessories Model WC 15 Fantech 0-100% variable speed controller ( 115V) Rotary speed controller with on - off switch 5 amp. I called the supplier and they said that the controller I have puts out around 122 volts to 70volts. He said that I could slow it down more but I would have to go to someone like grainger to get the advice and what I would need. He stated that the fan was capable of running at a slower speed but he did not have what I needed. Any ideas. Thanks. This is installed in a flexable insulated duct, so putting a damper on the inlet I would think may collapse the duct pipe. the inlet of this pipe is connected to the furnace outlet plenum.

the damper would be directly at the fan inlet- not the end of the inlet duct

OK, you have your answer. Now you need a speed controller based on what you were told that this operates at 70-120VAC. Take a look at:

http://www.harborfreight.com/router-speed-control-43060.html

There are starting and stalling issues if you try to operate below a characteristic speed/voltage. The fan people would design the controller supplied within 'reliable start/run parameters'.

Going outside those is not advisable. I.e. by using an even lower voltage.

I am not a big fan <pun) of starving a 'whole fan' of intake, as it can lead to motor cooling issues.

Therefore what I would suggest is circumferential masking to reduce the fan tips access to air and assure flow past the motor is maintained. "Tips" do most of the "velocity work"

This would be say a 10" hole in a plate, or disc, fitted directly on the suction side of the fan shroud. Then increase or decrease hole dia till you find your desired flow.

That was my first concern after looking at the data for this fantech product. Which maybe the reason they do not run below 70V, although they claim 0-100% speed control. Personally, I would not have installed this in my duct work at home. And even after the OP said that they themselves didn't know an listed Grainger as a contact to talk to. Anyone selling any product and does not know everything about it, do not buy it from them. That said, I wold not install one of these in anyone's home or business.

Thinking further about the whole design, I would have installed the blower on the intake side of the heater, whereas it appears to have been installed in the hot air distribution side which makes motor cooling even more of a concern......

Assuming that this is OK perhaps an adjustable bleed duct/diverter take off after the blower feeding back to the heater input ..... presumably the heater is thermostatically controlled so a proportion of warmer intake air would not affect output temperature, the blower motor would get full throughput, but the destination would get only as much air as required, and be more adjustable - depending on the diverter chosen - plus the blower speed control

I know you said the fan is hard to get at (which is to my mind almost a cardinal failure in itself!), but if you could take it out, attach power and use something to cut 30% off the blades, then run it against a file to get them all the same length and weight!!

That will severely reduce the thru put!!

I would like to thank everyone for there input. I have found the solution, I called Fantech the Co. not a supplier, I got in touch with the tec department. easy fix, I told the man what I was doing and the problem, He said that I had everthing that I needed, I should remove the face plate on the speed control and look for a small screw, it would be marked witch way to turn and the factory setting was only around 20% and I could get any speed that I needed and the fan was designed for it. No problem and Problem solved.

There ya go. When all else fails, call the MFG. Glad you have solved your problem