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Old 08-25-2009, 12:44 PM   #1
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Adding duct fan to HVAC


I have a room that doesn't get enough air flow from the main air handler. I'd like to add a centrifugal force inline duct fan to help "balance" the airflow to the room. However, the ducts where the fan would be installed is in the attic and the air handler is in the basement. I need to be able to turn the fan on and off with the airhandler. I tried using a sail switch to no avail. It's quite difficult to run wires unless I ran them through the ducts (doen't sound like a good idea).

Is there a wireless control device that would be able to sence when the airhandler is running and send a signal to the attice fan?

Any other ideas or comments are welcome.

thanks,

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Old 08-25-2009, 03:20 PM   #2
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Adding duct fan to HVAC


A fan that runs on 24vac?
A fan that runs on 120vac with a 24vac relay controlling it?
The 24vac sail switch would activate either of these options.

If you are allowed to use the ductwork as a 24vac return you need only one wire.

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Old 08-25-2009, 04:03 PM   #3
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Adding duct fan to HVAC


Yoyizit,

Thanks for the reply. I'm sorry I didn't include this important information. The fan I wish to control runs on 120VAC @ 2A. Also, the duct work that I have in the house is a combination of duct board and flexible. So I can't use your one wire suggestion unfortunatly.

The sail switch I used was mounted inside the duct board. I used it with another fan in the past that didn't have enough "push". This new fan strong enough that it no longer allows the switch to turn off. Hence, the need for another appoach.

Is running wire through the cold air return ducts a "no-no"?

Thanks,
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Old 08-25-2009, 04:29 PM   #4
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Adding duct fan to HVAC


Quote:
Originally Posted by empeters View Post
This new fan strong enough that it no longer allows the switch to turn off.
1
Is running wire through the cold air return ducts a "no-no"?
2
1 Reduce the size of the sail.
2 For 24vac I can't imagine a rule prohibiting this, but you may want to get wire with moisture-resistant insulation.
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Old 08-25-2009, 04:42 PM   #5
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Adding duct fan to HVAC


(I don't know how to do the "quote" box but will reply using your number schem)
1. Tried making sail smaller. I can't seem to achieve the correct balance that will close sail contacts when air handler on and open contacts when air handler is off.

2. I might want to consider this approach. I managed to find a wireless solution that's exactly what I need but it costs about $290.00. I probably shoudn't be surprised.

Thanks,
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Old 08-25-2009, 04:50 PM   #6
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Adding duct fan to HVAC


Quote:
Originally Posted by empeters View Post
(I don't know how to do the "quote" box but will reply using your number schem)
1. Tried making sail smaller. I can't seem to achieve the correct balance that will close sail contacts when air handler on and open contacts when air handler is off.
The sail return spring may be weak or gummed up. If the sail switch without the sail on it doesn't open then you need a new switch.

Or you could make your own with a microswitch
http://img.alibaba.com/photo/50358221/Micro_switch.jpg
[a few bucks, see below]
and a homemade sail.

A suitable relay & wiring can be had from Hosfelt.com, Digi-key, Mouser or Jameco for a few bucks and some 2 hours labor. For $290 I'd sure DIM [Do It Myself].
The xformer should be a bell xformer; they're short-circuit proof. Or use a fused Hosfelt 'former.

Last edited by Yoyizit; 08-25-2009 at 04:55 PM.
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Old 08-25-2009, 06:38 PM   #7
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Adding duct fan to HVAC


I understand the relay and the wiring, what about hte xformer (transformer). I assumed I'd use a 24VAC relay. Is a transformer still required. If so, how do I connect it all together?
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Old 08-26-2009, 03:27 PM   #8
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Adding duct fan to HVAC


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I understand the relay and the wiring, what about hte xformer (transformer). I assumed I'd use a 24VAC relay. Is a transformer still required. If so, how do I connect it all together?
The 24vac 'former is connected in series with the sail switch and the 24vac relay coil, and the 'former powers the relay coil.
The relays contacts, rated at 2A (motor load) and 120vac are in series with the fan and a 120vac source.
That way the wires through the ducts only carry 24vac at small current and small power.
If you have a bell 'former in your house you can use it, but the relay coil voltage must match the 'former voltage, and the 'former has to deliver enough current to pull in the relay and work your door bell.

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