# Running wire through a cold air return?



## beezlebub03

Hi, 

I'm planning to run a new 15 amp circuit to a new ceiling fan in my living room while minimizing destruction of my walls and ceilings. I just realized I have a cold air return that runs half the length of my house and could serve as a good, obstruction-free conduit for running wiring where I need it to go. This cold air return isn't a traditional metal vent. It's merely an un-insultated joist bay in my finished basement. I'm assuming there's no unusual temperature variation - there's just room temp air being pulled through this joist bay towards the furnace. 

*Anybody have any idea if it's kosher to run electrical wiring through something like this?* 

thanks.


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## Pudge565

oh oh pick me pick me i know the answer. you cannot run the wire like you propose. in an air handling space you may only run wires perpendicular to the duct. not sure what code off hand but it is code.


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## brmax

*ent*

i ran across an article from Carlon ent flex and rigid conduit that had something of that, its 82 pages i believe
carlon.com


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## micromind

According to the 2005 NEC, 300.22 (B), MC cable, EMT, IMC, and rigid can be run in "ducts or plenums specifically fabricated to transport environmental air." Type NM cable (Romex) is not allowed inside of a duct. 

The trick here is that all of these conduits need to be fastened at certain intervals, that can be difficult inside of a duct that's too small to crawl through. 

Rob


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## nap

No, it is not Kosher to run a circuit through the duct.

the biggest reason is:

anything is a duct or plenum space must be plenum rated. That means it is specifically designed to not emit above a determined level of toxic fumes when exposed to fire.

typical NM is not plenum rated.


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## Termite

nap said:


> the biggest reason is:
> 
> anything is a duct or plenum space must be plenum rated. That means it is specifically designed to not emit above a determined level of toxic fumes when exposed to fire.
> 
> typical NM is not plenum rated.


This is 100% correct. Nothing to do with securing the wire. You can run appropriate wires through a plenum, but what you're talking about is a DUCT, and you just can't use a duct as a conduit. 

Very bad idea. Hypothetically, if you were to do this, how would they clean the ducts? It would wreck the wire. Find another way to route the wire.


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## Tattoo

Great points guys but I think and I may be wrong but the OP is considering using a cold air return for the wiring path.... here in the north we see this on a regular basis for new home construction..... This is not a duct.... typically a void.... Interesting that this is against code in the US.

Cheers


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## nap

Tattoo said:


> Great points guys but I think and I may be wrong but the OP is considering using a cold air return for the wiring path.... here in the north we see this on a regular basis for new home construction..... This is not a duct.... typically a void.... Interesting that this is against code in the US.
> 
> Cheers


yes, that is a duct. A cold air return duct. Just because is uses the floor and 2 floor joists and a sheet of metal for the walls of the duct, it is still a duct.

The problem is if for some reason there would be a fire, the non-rated plastic in the duct, plenum, void, whatever you want to call the space used to confine a column of air and directs it to another area, would transport the smoke deveopled from the heated/burned plastic to other area of the building.


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## Silk

nap said:


> yes, that is a duct. A cold air return duct. Just because is uses the floor and 2 floor joists and a sheet of metal for the walls of the duct, it is still a duct.


 
It is not a duct, it is "Other Space Used for Environmental Air" which falls under Article 300.22(C). The exception to 300.22(C) permits NM cable to be run perpendicularly through the cold air return space. 

So the OP can cross through the cold air return space between the joists, but he cannot use it as a raceway.

Here is the NEC text:

(C) Other Space Used for Environmental Air This section applies to space used for environmental air-handling purposes other than ducts and plenums as specified in 300.22(A) and (B). It does not include habitable rooms or areas of buildings, the prime purpose of which is not air handling.
FPN: The space over a hung ceiling used for environmental air-handling purposes is an example of the type of other space to which this section applies.
_Exception: This section shall not apply to the joist or stud spaces of dwelling units where the wiring passes through such spaces perpendicular to the long dimension of such spaces._​Section 300.22(B) specifically states that ducts or plenums are specifically fabricated to transport environmental air.


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## robut

*romex through the air duct*

Ok 
How does one run a romex to the other side of the basement with out passing through the cold air return?

My cold air return runs through the center of my basement which is two joist with sheet metal between them.

Can I use 1/2 " reg. metal conduit? to contain the romex from damage?

I have been looking at this for quite a while, wanting to add an outlet on the other side of the basement.
Deck hand.


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## Silk

You can run straight through the return air space between your joists, you can't run along the return air space. Perpendicular, not parallel.


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## Tattoo

Silk said:


> It is not a duct, it is "Other Space Used for Environmental Air"


I didn't think I was losing my mind.... although it has been a long week:laughing::laughing:


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## nap

Silk said:


> It is not a duct, it is "Other Space Used for Environmental Air" which falls under Article 300.22(C). The exception to 300.22(C) permits NM cable to be run perpendicularly through the cold air return space.
> 
> So the OP can cross through the cold air return space between the joists, but he cannot use it as a raceway.
> 
> Here is the NEC text:
> 
> (C) Other Space Used for Environmental Air This section applies to space used for environmental air-handling purposes other than ducts and plenums as specified in 300.22(A) and (B). It does not include habitable rooms or areas of buildings, the prime purpose of which is not air handling.
> FPN: The space over a hung ceiling used for environmental air-handling purposes is an example of the type of other space to which this section applies.
> _Exception: This section shall not apply to the joist or stud spaces of dwelling units where the wiring passes through such spaces perpendicular to the long dimension of such spaces._​Section 300.22(B) specifically states that ducts or plenums are specifically fabricated to transport environmental air.


 The exception above, as I see it, is in reference to 300.22(C) which means the area we are speaking of is not included within (C). I do not see where the type of build we are speaking of is not considered a plenum or duct. By adding a cover over the open areas of the cavities, would that not be specifically make it a duct specifically designed to carry environmental air?

. Here is an excerpt from a poster on Mike Holts forums concerning this:



> the stud bays or joist bays are not considered plenum spaces unless the space itself is used as a 'duct' or plenum. If a duct is installed in the space, it usually means that the duct is doing the job of a plenum, not the wall cavity.


Doesn't make him right but it does make him on my side.

Regardless of the outcome of that argument, OP wants to run lengthwise through the space, which still is not allowed in any of the sections. OP can still not do what he asked if he can do.


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## Termite

It is either a plenum or a duct. And it isn't a plenum. Sorry, it is a duct.


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## Silk

thekctermite said:


> It is either a plenum or a duct. And it isn't a plenum. Sorry, it is a duct.


 
Sorry it is "Other Space Used for Environmental Air". It does not have to be either a duct or a plenum.

The code states that a duct or a plenum is "*specifically fabricated to transport environmental air*"

A stud or joist cavity is not fabricated to transport environmental air, it is something that is "*altered* to be able to transport environmental air.

If it is either a duct or a plenum, then there would be no need for Section 300.22(C) because what it covers wouldn't exist.

Section 300.22(C) exception specifically addresses this type of situation
_Exception: This section shall not apply to the joist or stud spaces of dwelling units where the wiring passes through such spaces perpendicular to the long dimension of such spaces._​It says that Section 300.22 does not apply to this situation. The section is titled "*Wiring in Ducts, Plenums, and Other Air-Handling Spaces". *

The exception says this section does not apply to this situation, therefore we cannot call it a duct or a plenum, by the NEC rules.

P.S. -- I was wrong about calling it an "other air-handling space", because if it doesn't apply to this section, it cannot even be referred to as that, because that is part of the section.


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## Termite

Ok, now that the issue is thoroughly clouded, do we all at least agree that he can't use this cold air return non-duct thing as a raceway, and can only run wires across it?


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## MacRoadie

Ok, my 2 cents. First of all, the OP stated that the referenced joist bay runs half the legth of his house. The Code limits concealed spaces to 10' vertical and 10' horizontal. Under normal conditions, this bay would have blocking to limit any concealed space to 10' or less. As this is not the case, we are left to assume that this joist bay was specifically designated to carry the return air and by definition is a plenum. 

Whether or not it is "finished" is not germaine to the original question, but raises another question regarding it's fire-resistance. There are 1000's of homes all over the western US with HVAC units sitting on garage platforms which also serve as the return air plenum, but they are always lined with sheet rock and this joist bay probably should have been too as it can serve as a conduit for flame, smoke, and combustion gases (see the other thread regarding fire stops and fire blocks).

As the joist bay was designed to carry that return air, the previous post stating: 



> [2005 NEC, 300.22 (B), MC cable, EMT, IMC, and rigid can be run in "ducts or plenums specifically fabricated to transport environmental air." Type NM cable (Romex) is not allowed inside of a duct.


would seem to apply.


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## Lansing

Its bad business to do that...The answer is no...:no: My Uncle a master electican said a good electican wouldn't do that anyway...


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## nap

Silk said:


> Sorry it is "Other Space Used for Environmental Air". It does not have to be either a duct or a plenum.
> 
> The code states that a duct or a plenum is "*specifically fabricated to transport environmental air*"
> 
> A stud or joist cavity is not fabricated to transport environmental air, it is something that is "*altered* to be able to transport environmental air.
> 
> If it is either a duct or a plenum, then there would be no need for Section 300.22(C) because what it covers wouldn't exist.
> 
> Section 300.22(C) exception specifically addresses this type of situation
> _Exception: This section shall not apply to the joist or stud spaces of dwelling units where the wiring passes through such spaces perpendicular to the long dimension of such spaces._​It says that Section 300.22 does not apply to this situation. The section is titled "*Wiring in Ducts, Plenums, and Other Air-Handling Spaces". *
> 
> The exception says this section does not apply to this situation, therefore we cannot call it a duct or a plenum, by the NEC rules.
> 
> P.S. -- I was wrong about calling it an "other air-handling space", because if it doesn't apply to this section, it cannot even be referred to as that, because that is part of the section.


silk, did you notice that that exception follows 300.22(C) that starts out with:




> (C) Other Space Used for Environmental Air *This section* applies


 
I read that as the exception refers to THAT section, not the entire group of sections.

and to:



> The code states that a duct or a plenum is "*specifically fabricated to transport environmental air*"


 
where does it state that?

and to:



> A stud or joist cavity is not fabricated to transport environmental air, it is something that is "*altered* to be able to transport environmental air.


you are right. a joist cavity is not fabricated to transport air. It would leak a whole lot but adding the 4th side is altering yes, but isn't altering a synonym for specially fabricating?


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## Silk

nap said:


> where does it state that?


 
Right Here:


(B) Ducts or Plenums Used for Environmental Air. Only wiring methods consisting of Type MI cable, Type MC cable employing a smooth or corrugated impervious metal sheath without an overall nonmetallic covering, electrical metallic tubing, flexible metallic tubing, intermediate metal conduit, or rigid metal conduit without an overall nonmetallic covering shall be installed in *ducts or plenums specifically fabricated to transport environmental air*. Flexible metal conduit shall be permitted, in lengths not to exceed 1.2 m (4 ft), to connect physically adjustable equipment and devices permitted to be in these ducts and plenum chambers. The connectors used with flexible metal conduit shall effectively close any openings in the connection. Equipment and devices shall be permitted within such ducts or plenum chambers only if necessary for their direct action upon, or sensing of, the contained air. Where equipment or devices are installed and illumination is necessary to facilitate maintenance and repair, enclosed gasketed-type luminaires shall be permitted.
​


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## Silk

Now that you guys have made me dig through old boxes in order to find the last handbook that I bought which is a 1999, maybe this should put the arguement to bed.

I will try to photocopy it, here goes:


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## Silk

OK, I screwed that up. The second image is the first page, the first image is the second page.

The explanation for Section 300.22(C) reads as:

Section 300.22(C) applies to other spaces used to transport environmental air that are not specifically manufactured as ducts or plenums,....................... and on, and on (I'm tired of typing)

The expanation for Section 300.22(C)exception reads as:

The exception to Section 300.22(C) permits cable to pass through joist or stud spaces of a dwelling unit, as illustrated in figure 300.19. The joist space is covered with sheet metal and used as a cold-air return for a forced warm-air central heating system.

Now to explain further. The NEC Handbook is written by the NFPA, which is the same people that write the NFPA 70, which is what we refer to as the Codebook. So I believe that we can all agree that if we are arguing semantics of NFPA 70, that the handbooks interpretation is the correct one, as it is written by the same people to explain their intentions.

To summarize: If we are going to be reciting code on what is a duct or a plenum, we cannot use our own interpretation of what that is. We must use the NFPA codebook and their associated clarifications in the NFPA 70 Handbook.


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## Silk

Lansing said:


> Its bad business to do that...The answer is no...:no: My Uncle a master electican said a good electican wouldn't do that anyway...


 
I am a master electrician, I have many freinds that are master electricians, and we are all "good" electricians. The only difference is that we know the code.

If I had a dime for everybody who had an uncle or a brother-in-law or a monkey's uncle who is supposed to be a master electrician that told me how I'm suppposed to do something............... I would be the richest man in the world!

I just wish people would refrain from the " my uncle says........."


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## Silk

nap said:


> . Here is an excerpt from a poster on Mike Holts forums concerning this:
> 
> 
> 
> Doesn't make him right but it does make him on my side.
> 
> 
> 
> Just because somebody posted their opinion on a Mike Holt Website doesn't mean that Mike Holt agrees with them or you, he has more than likely never read 99% of the postings, he just hosts the site and pays the bills
Click to expand...


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## nap

Silk said:


> nap said:
> 
> 
> 
> . Here is an excerpt from a poster on Mike Holts forums concerning this:
> 
> 
> 
> Doesn't make him right but it does make him on my side.
> 
> 
> 
> Just because somebody posted their opinion on a Mike Holt Website doesn't mean that Mike Holt agrees with them or you, he has more than likely never read 99% of the postings, he just hosts the site and pays the bills
> 
> 
> 
> Remember, I didn't say he was right:wink: GW gets to cite such people all the time. Why can't I?:laughing:
> 
> I am a licensed electrician myself so I do not argue from a point of ingnorance either. I do respect the handbook and will accept their interpretation. It wasn't that I wasn't truly acccepting yours either silk. Just that I disagreed with some of your interpretation such as this:
> 
> 
> 
> 
> Quote:
> The code states that a duct or a plenum is "*specifically fabricated to transport environmental air*"
> 
> where does it state that?
> 
> Click to expand...
> 
> and your reply of:
> 
> 
> 
> 
> 
> covering shall be installed in *ducts or plenums specifically fabricated to transport environmental air*.
> 
> Click to expand...
> 
> it still does not state that the consctuct we are speaking if is not a plenum or duct. It simply states that that section refers to ducts or plenums that are specifically constructed to carry air. My position is that it is a duct but the code does not consider it so for the purposes defined within this section because of the type of construct. Regardless how it is built or the rejection of my thought that it is a construct specifically built for the purpose, it is still a duct by virtue of its use. You know, if it walks like a duct and it talks like a duct, its a duct.:whistling2: I know it is beating a dead horse but bottom line, it is a duct, just not within the codes definition of one specifically built for the purpose.
> 
> 
> 
> 
> 
> So, bottom line; the OP still cannot do what he asked if he could do and we are all more clear on the rest of the code as well:thumbsup:
> 
> 
> 
> 
> 
> 
> I just wish people would refrain from the " my uncle says........."
> 
> Click to expand...
> 
> Hey, if you can't count on family, who can you count on? Mi famiglia is always backin' me up.
> 
> Oh, forget I said that. I don;t really have any famiglia. Nope. none. No such thing.:whistling2:
> 
> Click to expand...
Click to expand...


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## Silk

nap said:


> Remember, I didn't say he was right:wink: GW gets to cite such people all the time. Why can't I?:laughing:
> 
> .


 
It's all good:thumbsup:

But who is GW?


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## Lansing

Silk said:


> I am a master electrician, I have many freinds that are master electricians, and we are all "good" electricians. The only difference is that we know the code.
> 
> If I had a dime for everybody who had an uncle or a brother-in-law or a monkey's uncle who is supposed to be a master electrician that told me how I'm suppposed to do something............... I would be the richest man in the world!
> 
> I just wish people would refrain from the " my uncle says........."


My Uncle John was never a monkey's uncle but your intitled to your opinion on him though I bet you would never say that to his face...But what about my answer?? was it right or wrong ??or do you even know ??:huh:


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## nap

Silk said:


> It's all good:thumbsup:
> 
> But who is GW?


our beloved (cough, cough) president. He has a lot of yes men telling him he is doing right and well. Doesn't mean he really is.

lansing: silk was not calling you a monkey (therefore your uncle would be a monkey's uncle). He was simply stating how often many people tell of somebody they know that is, (whatever) and they must be right.

bottom line:

it is ok and acceptable to run NM across the type of air "duct" we were discussing but it is not acceptable to run in lengthwise inside of it.

In a residential setting, this is a normal situation as a floor or wall stud cavity is often used to direct air throughout areas of the house, especially when there are multiple floors and/or a basement. The code does allow the NM to be run though (crossways) those areas. I don;t like that they do allow it but they have more money than me so what I want does not always matter.


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## HandyPete

interesting post. (nice work silk)

it's only a house, and any good electrician (excluding monkeys) will know how to run a stupid cable anywhere in that building! forget the "whatever" and just run the cable somewhere else.

- pete


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## LawnGuyLandSparky

beezlebub03 said:


> Hi,
> 
> I'm planning to run a new 15 amp circuit to a new ceiling fan in my living room while minimizing destruction of my walls and ceilings. I just realized I have a cold air return that runs half the length of my house and could serve as a good, obstruction-free conduit for running wiring where I need it to go. This cold air return isn't a traditional metal vent. It's merely an un-insultated joist bay in my finished basement. I'm assuming there's no unusual temperature variation - there's just room temp air being pulled through this joist bay towards the furnace.
> 
> *Anybody have any idea if it's kosher to run electrical wiring through something like this?*
> 
> thanks.


Back to the OP... WHY are you running a new 15a circuit to add one lousy measly little ceiling fan? You dop know these things use all of 100-150 watts, right?


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## Silk

Lansing said:


> My Uncle John was never a monkey's uncle but your intitled to your opinion on him though I bet you would never say that to his face...But what about my answer?? was it right or wrong ??or do you even know ??:huh:


 
Yes I do know, you're wrong...................... and so is your uncle:thumbsup:


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## skirack

*Plenum Rated Cable?*

The OP originally asked about running Romex through a joist cavity being used as a cold air return. I'm trying to accomplish a similar task. Someone else said that it could be done if it is in a conduit or MC type cable. 
Is this accurate? Is there any electrical cable rated for plenum use? (BX / MC, etc...)?


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## Klawman

But nm in the space enclosed by joists and the ceiling of one story and the floor of the next can be used as a raceway for nm, can it not, as long as the space isn't being used for routing air for heating or cooling, yes? I did that for cable to a ceiling fan and light, while stapling the cable half way up the side of a joist.


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## nap

skirack said:


> The OP originally asked about running Romex through a joist cavity being used as a cold air return. I'm trying to accomplish a similar task. Someone else said that it could be done if it is in a conduit or MC type cable.
> Is this accurate? Is there any electrical cable rated for plenum use? (BX / MC, etc...)?


If it were me and I needed to cross a cavity that is being used as a duct or plenum (trying to avoid that argument again), I would use a piece of EMT large enough to comfortably put the NM through it and seal the ends of the EMT to the studs/joists with a fire caulk. While this is not necessary, I believe it provides for the best installation as the NM, if exposed to excessive heat, will not gas off toxic fumes into an air handling space and where the stud/joist is penetrated, there will be no air leakage.



in the code section concerning duct and plenums, MI and MC (only that type with a continuous smooth or corrugated outer sheath without a non-metallic outer layer (in other words, not the typical MC with the spiral wrap metal sheath as well as any MC that has an outer non-metallic sheath) is allowed as well as solid metal conduits (FMC has very limited and specific uses allowed but not as a general wiring method.) 

in "other spaces used for environmental air", basically, the material needs to be listed for use in a plenum air space.

If that doesn't make sense. let me know. I realize it is confusing as written but trying to avoid excessive verbiage.



Klawman said:


> But nm in the space enclosed by joists and the ceiling of one story and the floor of the next can be used as a raceway for nm, can it not, as long as the space isn't being used for routing air for heating or cooling, yes? I did that for cable to a ceiling fan and light, while stapling the cable half way up the side of a joist.


correct. the problem comes in when the cavity is being used as an air transfer space that could conceivably cause toxic gases to be spread throughout the building should the plastic sheath be exposed to excessive heat.


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## Maximo

Wow! Now I know why I joined this chatroom. Gret stuff people.


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## J. V.

Lansing said:


> Its bad business to do that...The answer is no...:no: My Uncle a master electican said a good electican wouldn't do that anyway...


My uncle is a truck driver and he says its okay to do it. 



Maximo said:


> Wow! Now I know why I joined this chatroom. Gret stuff people.


Welcome to the forum. :thumbsup:


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## nap

J. V. said:


> My uncle is a truck driver and he says its okay to do it.
> 
> :


all my uncles are deceased and they didn't have anything to say about the subject.





did that cross the line?


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## J. V.

nap said:


> all my uncles are deceased and they didn't have anything to say about the subject.
> 
> 
> 
> 
> 
> did that cross the line?


No. :laughing:


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