110 volt wiring in heating duct

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  #1  
Old 06-28-07, 11:24 AM
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110 volt wiring in heating duct

i'd like to add a small fan to one register, to boost air flow in that room. the walls are finished everywhere, and cosmetics are important for this situation.
i want to power the fan from the furnace supply and run 110 volt through the ducting to the register, and install a small box fan inside the register. there is no way to run the wiring alongside the outside of the duct.
i will not violate code, etc, so i need wire that can be run through a heating duct.
does it exist? what is it called?
thanks!
 
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  #2  
Old 06-28-07, 11:29 AM
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Sorry no go. Yes, you can run the wire OUTSIDE the duct. Do it that way.
 
  #3  
Old 06-28-07, 12:23 PM
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How about something like this:

http://www.atrendyhome.com/durebofan.html
 
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Old 06-28-07, 06:50 PM
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duct booster

Will, your suggestion would be ideal except that i really want to hide the wire. (and the duct happens to be a different size, to boot).
i had used a duct booster in my previous home, but this was in an accessible place and served a couple of rooms in one wing. this situation is for only one room at the end of a trunk, so i dont really want to boost everything.

Bob, thanks for the official word. i have spent hours trying to fish the space, but it's simply impossible. i'm curious - is the problem the temperature (the wire should be rated to 105C, which is a LOT hotter than the duct), or is it the fumes the wire would give off if it burned, or what? the duct would seem to be a pretty safe place for wire, once it is installed.
Bruce
 
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Old 06-28-07, 07:43 PM
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I'm no expert, but the cables have to be plenum rated, and I have not seen any plenum rated cabling for 120v applications. I've only seen them (google) for communications type cabling.
 
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Old 06-28-07, 08:20 PM
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It seems to me that I read somewhere in ECM that if the device is directly used on environmental air then if the wiring is in emt or a few other types of metallic raceways it is allowed.
Cant seem to find an acceptable source for that statement but it sticks in my little brain just the same.


Roger
 
  #7  
Old 06-28-07, 08:25 PM
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Bruce, anything can be wired. You may have to cut open a wall or two, which I suspect you don't want to do.
 
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Old 06-28-07, 08:35 PM
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Bob I found the article that was stuck in my mind.... how do you read it??


http://www.ul.com/regulators/ode/1101.pdf


roger
 
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Old 06-28-07, 09:16 PM
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Wink

I have found a long long time ago that there is no fan that is made that will work good in the duct work. you are better off to rework the duct work some. Or put in balance dampers like you should have. So you can get the CFM you need at that register
 
  #10  
Old 06-29-07, 06:39 AM
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I believe the major issue is that stuff inside ducts can spread noxious fumes rapidly if they catch fire. That's why you have to be very careful what you put inside a duct.
 
  #11  
Old 06-29-07, 08:08 AM
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Also, the inside of ducts have razor sharp edges and pointy sheet metal screws everywhere. I can't imagine how you could pull a cable (even plenum rated AC metal cable) through without damaging it or getting snagged. You couldn't assemble conduit in the duct without disassembling the duct itself which would defeat the point. Finally, how would you make the connections at the register? You'd need a junction box. If it was in the duct, it would need to be plenum rated with plenum rated cord-and-plug (if such a thing exists). If there's a j-box in the duct it would obstruct the flow so much that you probably wouldn't be any better off with the fan running.
 
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Old 06-29-07, 08:36 AM
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Guys, a whole bunch of valid points.

i suppose i could string BX through the duct, but that would technically not deal with the issue of fumes. i suppose if i put a whisperfan behind the grille, it is not *in* the duct (hmmm...). i could put a jbox within the wall, punch a hole through the register boot to bring the bx (and fan wire) into the box. of course, my wife's idea is to buy a $30 electric fan-heater and put it on the floor. that's the practical solution, no doubt.


if i had owned the house when these renovations were done, things would be very different. but the previous owner finshed the basement, and all the dampers and stuff are behind sheetrock.


i had used - and been quite satisfied with - a squirrelcage fan that impinged into a trunk in my previous house, because it did boost the flow in the entire trunk, and basically rebalanced the house. external wiring was not a problem in that situation.

in this situation, the cure (redoing the ducting, dampers, etc) would introduce an unconscionable cost and inconvenience because things have been painted, papered, etc.

thanks, all.
 
  #13  
Old 06-29-07, 08:43 AM
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"behind sheetrock" is not an impenetrable barrier. Drywall is dirt cheap and extremely easy to cut and repair. In my opinion, people go to all sorts of unreasonable extremes to avoid opening up the drywall.
 
  #14  
Old 06-29-07, 10:34 AM
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behind drywall in several rooms that have been painted. in other words, it requires a *lot* of labor. maybe in my house but not in the one i share with my wife.
 
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Old 06-29-07, 04:29 PM
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I would agree with unfinished drywall or painted drywall. However cutting up textured ceilings or walls or wallpapered drywall is another story.


Roger
 
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