electric wiring in air duct

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  #1  
Old 10-03-05, 10:26 AM
Raskolnikov
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electric wiring in air duct

Hi,

I have an old house and there no way i can wire in the walls, for example to put a plug on the second floor. Is there any problem with passing electric wires in the air ducts of the heating system? The air in the ducts is never really hot; just a bit above room temperature. It would be a very easy solution for me, since I have two air ducts up to the second floor...

Thanks -

Rask.
 
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Old 10-03-05, 10:54 AM
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There are certain type of wire that you can run in return air ducts. However, this is generally frowned upon.

It would be better to find another route for the wires.
 
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Old 10-03-05, 11:14 AM
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Do you mean the forced air ducts or the cold air return cavities? As racraft said, you potentially could use the return cavities with the proper cable; but it's not a good idea. You cannot use the suppy ducts at all.

You will be much better off finding a different path for the wiring to the second floor. Sometimes a reasonable solution is to run conduit from the basement up the exterior of the house and into the attic. You can then fish wire down interior walls. Sometimes surface mounted conduit is appropriate like Wiremold products. Sometimes you can run a conduit up through the back of a first floor closet or other hidden location. Look for gaps next to your plumbing vent stack. You are allowed to fish romex along that if you can find a space.
 
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Old 10-03-05, 11:29 AM
Raskolnikov
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I would use the supply duct. Why is it a problem passing a wire there? I was thinking to pass a wire for my computer, which uses a powerbar.

Thanks for the answers...
 
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Old 10-03-05, 11:36 AM
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The problem would be with the potential to spread smoke and fire throughout via a ready made chimney called the ductwork.
 
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Old 10-03-05, 01:15 PM
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What about running a raceway on the exterior wall and up to the second floor? Are there any plumbing pipes/drain lines between the first and second floors? You can try to route cable adjacent to the pipes.
 
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Old 10-03-05, 01:40 PM
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Originally Posted by Raskolnikov
I would use the supply duct. Why is it a problem passing a wire there? I was thinking to pass a wire for my computer, which uses a powerbar.
There are a number of reasons. The ductwork could quickly spread an electrical fire. There is no approved method of entering the cable into or exiting from the ductwork. The very sharp metal in the joints and screws of the ductwork would easily pierce a cable and cause a short which can cause a fire or electrocute anyone who touches the ductwork. Cable is rated for use at normal ambient temperatures; the increased heat of the forced air system would require you to use special cable and de-rate for rather high temperatures. For these multiple reasons, electrical code does not permit running wiring in residential air ducts.

There are a number of good suggestions already posted here for adding a circuit in an old house.
 
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Old 10-04-05, 07:09 AM
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Originally Posted by Raskolnikov
I would use the supply duct. Why is it a problem passing a wire there? I was thinking to pass a wire for my computer, which uses a powerbar.

Thanks for the answers...
Another reason is that when a cable jacket burns, it gives off toxic fumes. When the wire is burried in a wall, the fumes do not get out very easily. When the wire is in an air duct, the heating/cooling system blows the toxic fumes all over the building. The class of cabling that can be used in return air plenums is called plenum cable. Its jacket either does not burn easily, or does not give off the toxic fumes (I don't remember exactly) But I do know that plenum cable is always much more expensive than regular cables. It is usually used above suspended ceilings in comercial environments where the area between the ceiling and the roof is used as the return air plenum.
 
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