DIY Home Improvement, Remodeling & Repair Forum

DIY Home Improvement, Remodeling & Repair Forum (
-   HVAC (
-   -   Wiring inline duct fan to blower motor (

cleininger 12-11-2006 08:41 PM

Wiring inline duct fan to blower motor
Hi folks,

I recently purchased an inline duct fan for a chilly room in our home and want to wire it to the furnace blower motor directly.

AFter studying the electrical schematic for a while, I thought I had it figured out. I connected the hot and neutral to the very posts on the control board that appeared to match what was feeding the blower but got nothing... it seemed I had completely broken the connection.

Anyone out there have any advice as to where I can connect these and how to connect them?

The schematic scan was too big to upload here so I've included a link to it: HERE

I've highlighted the wires I thought would work - orange goes to "HEAT", white is going to "NEUTRAL". the other 3 are going to "UNUSED MTR LEADS" and the "COOL" switch.

Any advice would be appreciated.

Hube 12-12-2006 07:21 AM

is this "in-line booster fan" 110 volts ? If it is, it only needs to have the 'hot/neutral leads connected to your units blower motor only. there is no need to go thru the units "Board".
note; in the majority of cases, these "booster fans are really unnecessary.Most weak supply runs can be boosted just by adjusting the dampers or registers on the other stronger runs.
Also , speed adjustments can be made to the main blower , which will send more velocity/volume to these "weak" runs.

cleininger 12-13-2006 10:03 PM

Thanks Hube...

Yes, it is 110 volts. I'm interested in knowing more about the speed adjustments. The furnace is a Heil however I was unable to find anything in the way of manuals and such online. The furnace is about 3 years old so it may be an outdated model. I was also unable to find a model number that wasn't specific to a part on the unit.

Generaly speaking, how might this speed adjustment be made?

Hube 12-14-2006 07:28 AM

Without knowing what make, model of unit it is make it very difficult to give exact advice.
Some furnace fan motors have pulleys that can be adjusted to lower or increase rpm.
Some motors have "speed taps" (low, med low, med hi high.)
You are best to leave these adjustments to a Hvac PRO

Note;the booster fan can be directly wired to the units original 110v fan motor by way of a hot,a neutral, and ground. Whenever the main fan comes on ,so will the booster.

Balance method;no booster fan needed.
By SLIGHTLY "dampering" or "throttling down" the air flow from some of the stronger supply runs, it will send MORE air to these less stronger runs, thus avoiding the installation of this booster fan.
Notice the emphasis on SLIGHTLY.
Without air measuring instruments this is a trial and error adjustment. Make sure you mark all original damper positions so you can relate to any adjustments.

glennjanie 12-14-2006 10:36 AM

Hello Cleininger:
Just a thought about the "weak" duct run in your house. I have found the weak run is usually run with flex-duct. While it makes for a quick and easy duct run, flex-duct is not conducive to free flow of air. I remember when it was first introduced the company cautioned us not to use a run over 3' long. I have found runs 40' long that could barely move a candle flame at the exhaust end. After I replaced the run with steel pipe with sleeve insulation the exhaust would blow the candle out! I just wondered if your weak run is flex-duct.

Hube 12-14-2006 04:42 PM

I sure do agree with the "improper" installation of flex.
If it is used as properly,eg ;approx 3'- 4' in length max,and fully extended ,so it keeps most of its actual inside diameter, it does a satisfactory job.
A lot of diyers (and also including some pros) get carried away in the seemingly easy installation and install this flex in a sloppy fashion like too many DROOPS, SAGS, unnecessary TWISTS , and TURNS,etc, all of which add restriction to any duct system.As an example ,even a badly installed 3 or 4 foot length of this flex could lose as much as 75 % of of its intended velocity/volume, As such, an intended 6 - 100 cfm , supply run installed with a piece of badly installed flex is hampered severely.(weak supply)

Another item to watch for when there is a "weak run to a room is to make sure there is adequate RETURN air for this room.You normally can only put as much supply in as there is taken out.

cleininger 12-23-2006 08:49 AM

Thanks for all of your input so far guys.

No, the pipe is not flex. The room however is in the basement at the end of a very long run and while the airflow is not great through the duct, obviously the location of the room is the biggest problem along with lack of proper insulation, air leaks, etc...

Additionaly, there is no return for this room. Perhaps I would be better off concetrating on adding one. I do have vent I already installed near the floor that is not being used.

glennjanie 12-23-2006 01:14 PM

Hello Cleininger:
Yes, the room will need a return air in order to get heat in it. If you already have a return air grille in the basement the vent you mentioned will be sufficient. Also you need to look at insulating both ducts, if they are not already insulated. If you are having trouble with air leaking in, you could add a 4" fresh air pipe from the outside or from the attic into the return air plenum at the furnace. The 4" fresh air comming straight into the furnace will create an "over-pressure" in the house and any air leaks will be to the outside rather than leaking cold air into the inside.

All times are GMT -6. The time now is 01:16 PM.