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Old 02-10-2012, 08:14 PM   #1
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Booster Fan Inline With Furnace Duct


Hello,

I have a room towards the back and north side of an old house, which is always cold. About 10 years ago, a contractor installed a fan in the duct to boost the level of heat to that room. It didn't work great but it did work better than if there was no fan at all. This year we have had lots of northern wind and that room has been cold again. I pulled the fan out of the duct and hard wired it to an outlet and it worked just fine. I wired it back up and screwed it to the duct with some of it exposed so I could see inside. I fired the furnace up and the fan does not work. It should switch on with the furnace fan. I followed the wires back to the furnace, which is new now and found the wires are clipped right as they reach the furnace cabinet. It looks like the HVAC contractors took a shortcut hoping none would be noticed. Well I noticed although it is 6 years to late.

I need to figure out a way to wire this booster fan to the furnace fan. Does anyone know where I can get a wiring diagram for this Tappan furnace? Or does anyone have a suggestion on using a relay wired between the thermostat and the booster fan to switch on the power?

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Old 02-10-2012, 09:52 PM   #2
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Booster Fan Inline With Furnace Duct


acc on the control brd provides 115 volts,This terminal will power up anytime blower turns on

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Old 02-11-2012, 07:26 AM   #3
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Booster Fan Inline With Furnace Duct


Taking that 115v from control board as coolmen suggests, to an externally mounted electrical box on back or side of furnace, will provide 'switched' power whenever blower fan turns on. Devices like humidifiers and booster fans can be plugged in like any appliance or tool and would then get power only when blower goes on.

The fan installed 6 years ago that may never have been on, has probably been blocking duct more than having no booster fan at all.
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Old 02-11-2012, 02:07 PM   #4
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Booster Fan Inline With Furnace Duct


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Taking that 115v from control board as coolmen suggests, to an externally mounted electrical box on back or side of furnace, will provide 'switched' power whenever blower fan turns on. Devices like humidifiers and booster fans can be plugged in like any appliance or tool and would then get power only when blower goes on.

The fan installed 6 years ago that may never have been on, has probably been blocking duct more than having no booster fan at all.
Thank you all for your responses. I can't find a terminal on the board that says 115V but there is a wire in the box that eventually ties into a switch on the outside of the furnace. This switch provides power to the furnace but I think it is on all the time. I saw in another post (using a search for booster fan) that a relay can be used between the power wire for the furnace fan and power wire for the booster fan. I think I may go this route. It is called a current sensing relay Generalaire B15-335 for $35.
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Old 02-11-2012, 02:29 PM   #5
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Booster Fan Inline With Furnace Duct


I have used that current sensing relay a few times...

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Old 02-11-2012, 02:33 PM   #6
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Booster Fan Inline With Furnace Duct


Just remember, you can push air into the room but without return air it will be far less effective at keep the room reasonably comfortable.

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Old 02-11-2012, 04:01 PM   #7
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Booster Fan Inline With Furnace Duct


The Tappon boards I've seen have EAC connections on their boards that should work for your fan if you can find it.
And as Jackofall says.. at the very least make sure the room air has a way of making itself back unrestricted to a return air grill so that the heated air flow is not limited by back pressure.
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Old 02-13-2012, 10:00 AM   #8
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The Tappon boards I've seen have EAC connections on their boards that should work for your fan if you can find it.
And as Jackofall says.. at the very least make sure the room air has a way of making itself back unrestricted to a return air grill so that the heated air flow is not limited by back pressure.
There is a EAC connection on the board. I am assuming this is the hot end, if so where would I wire the return to? Can I just splice this to the return current on the furnace switch (this power is on all the time) that is wired in to the furnace?
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Old 02-13-2012, 10:12 AM   #9
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Booster Fan Inline With Furnace Duct


Do not go near the primary switch (emergency shutdown).

The EAC terminals you found supply A/C current for the booster fan. Wire the booster fan to these and it will go on only when main fan turns on.
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Old 02-13-2012, 10:16 AM   #10
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.
It would be easiest for anyone following your wire work to connect the hot leg to the EAC terminal and the return line to a white board neutral terminal.

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