lighting in plenum

Merry Christmas
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gotmud

Senior Member
Location
some place cold
ok so bear with me...What I have is a new detached residential pool house we are wiring...the owner is worried about the attic above molding from all the moisture sooo the heating company is making the attic a wild return to keep air flow rolling through up there...I see per 300.22 that I now have to run MC cable up there now but can't seem to figure from the wording about lighting....

The pool house will have a 10' flat sheetrocked ceiling throughout and I want to install recessed cans all over. Now knowing the whole attic is a plenum area can I put the cans in??? or do I have to frame sealed boxes around all of them or ????? I guess I've never had the attic of a residential job a plenum and am confused on what I have to do....like I said I know I have to use MC for wire but what about lighing boxes and cans?? anything I have to know???? thanks guys (ohh and gals:))
 

raider1

Senior Member
Staff member
Location
Logan, Utah
If all this is being done is mechanical ventilation of the attic space I would not call it a "Plenum".

All attics (Except for some unventilated conditioned attic spaces) are ventilated in some manner whether by natural ventilation or mechanical ventilation.

Chris
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
If all this is being done is mechanical ventilation of the attic space I would not call it a "Plenum".

All attics (Except for some unventilated conditioned attic spaces) are ventilated in some manner whether by natural ventilation or mechanical ventilation.

Chris

I thought he was saying the attic itself is part of the return air for the furnace.
 

raider1

Senior Member
Staff member
Location
Logan, Utah
I thought he was saying the attic itself is part of the return air for the furnace.

If it is an unconditioned attic it is a violation of the mechanical code to take return air from that space.

What I envisioned was a mechanical ventilation system that will circulate and remove the air in the attic.

Chris
 

gotmud

Senior Member
Location
some place cold
from the mech room the heating guys will just run a return air duct to the attic off the furnace and stop.. they will then just cut in egg crate registers in 4 or 5 spots on the sheetrock ceiling so that would make the whole attic a return air...that is what I was told by HVAC guys...
 
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gotmud

Senior Member
Location
some place cold
If all this is being done is mechanical ventilation of the attic space I would not call it a "Plenum".

All attics (Except for some unventilated conditioned attic spaces) are ventilated in some manner whether by natural ventilation or mechanical ventilation.

Chris

Ok so lets call it a wild air return...
 

raider1

Senior Member
Staff member
Location
Logan, Utah
from the mech room the heating guys will just run a return air duct to the attic off the furnace and stop.. they will then just cut in egg crate registers in 4 or 5 spots on the sheetrock ceiling so that would make the whole attic a return air...that is what I was told by HVAC guys...

Ok so lets call it a wild air return...

Is this attic a conditioned attic assembly?

Is the insulation on the roof or on the ceiling joists?

If this attic is in fact going to be part of the return air then it would be "Other spaces for enviromental air" in regards to 300.22(C).

Chris
 

haskindm

Senior Member
Location
Maryland
This sounds like a very bad plan. Just install vented soffit and a vented ridge cap and let the attic ventilate itself. If they are concerned that this would not be sufficient, install an attic fan controlled by a humidistat. That would be MUCH more efficient than involving the HVAC. Sometimes the simple answers are the best.
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
Is this attic a conditioned attic assembly?

If it wasn't before, it will be after they start drawing the return air through it!!

Is the insulation on the roof or on the ceiling joists?
Not exactly an electrical issue, but I agree it would be bad to have the attic uninsulated.

Again, not an electrical issue, but they are going to draw air from the pool room through the attic to try to reduce moisture in the attic!!!

They are right to be concerned about moisture in the attic, but if I understood the description right, I don't think that is going to help. If the air from the pool is pulled up into a cold, uninsulated attic, its going to condense like crazy.

They are
 

raider1

Senior Member
Staff member
Location
Logan, Utah
If it wasn't before, it will be after they start drawing the return air through it!!

Not exactly an electrical issue, but I agree it would be bad to have the attic uninsulated.

Again, not an electrical issue, but they are going to draw air from the pool room through the attic to try to reduce moisture in the attic!!!

They are right to be concerned about moisture in the attic, but if I understood the description right, I don't think that is going to help. If the air from the pool is pulled up into a cold, uninsulated attic, its going to condense like crazy.

They are

My point with those questions is the the Mechanical code prohibits taking return air from an unconditioned attic, and for good reason.

I agree with an earlier post that a ventilation system with a humidistat would be a much better idea then trying to use the attic as part of the return air for the building.

Chris
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
My guess is that it is a sealed attic and the air will be coming from the building and not thru vents etc but it is just a guess.
 

gotmud

Senior Member
Location
some place cold
This sounds like a very bad plan. Just install vented soffit and a vented ridge cap and let the attic ventilate itself. If they are concerned that this would not be sufficient, install an attic fan controlled by a humidistat. That would be MUCH more efficient than involving the HVAC. Sometimes the simple answers are the best.

I 100% agree and mentioned this to them so ??? who knows...to explain this further...it will be a sealed attic i would guess, they are going to spray that expandable foam all up in the attic, on the roof trusses and in soffits, basically sealing up the attic...then blow in insulation on the ceiling portion of the attic....Sooo i would say yes it's a sealed attic...I understand it would be considered "other spaces". So what would be the process of installing recessed cans on the ceiling....would I have to build wood boxes up there to go over my cans to seal them up or ?????. if there all metal am I ok to do nothing...I just dont know about installing recesed in "other places"...what do you guys do when you have a wild return above drop ceilings in commercial and want to cut in recessed cans in the drop ceiling, basically it would be the same as that...
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I suspect a standard air tight can is plenum rated but not sure. I would call the manufacturer of the brand you use and find out. I have seen cans in a plenum so it can be done.
 

cadpoint

Senior Member
Location
Durham, NC
My question is; is the pool used all year long ? My thought is no! So should be weather proofed or not, that is the question, motor drained if it isn't and then totally insulated if it is used all year long...

My opinion is that one would need to insult the roof, and create (as said) slots or open venting to the ceiling. One could have the ceiling gypsum with a continual vent (exterior grade) of just stop the gypsum short but one foot all around.

The exhaust fan in roof should be in play.

It's only a pool house, depending on the owners wishes, work accordingly.
 
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gotmud

Senior Member
Location
some place cold
My question is; is the pool used all year long ? My thought is no! So should be weather proofed or not, that is the question, motor drained if it isn't and then totally insulated if it is used all year long...

My opinion is that one would need to insult the roof, and create (as said) slots or open venting to the ceiling. One could have the ceiling gypsum with a continual vent (exterior grade) of just stop the gypsum short but one foot all around.

The exhaust fan in roof should be in play.

It's only a pool house, depending on the owners wishes, work accordingly.

I have to admit, I have no idea what your even talking about.:confused::confused: I'm asking about recessed cans in a wild return and your talking about :confused::confused:insulation building codes???..I think... also I can't work on the owners wishes I have to go off of my inspectors wishes in this case....Really I think it all comes down to, can an air tight can be in a wild return in "other spaces" without boxing them off.
 
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kwired

Electron manager
Location
NE Nebraska
I have to admit, I have no idea what your even talking about.:confused::confused: I'm asking about recessed cans in a wild return and your talking about :confused::confused:insulation building codes???..I think... also I can't work on the owners wishes I have to go off of my inspectors wishes in this case....Really I think it all comes down to, can an air tight can be in a wild return in "other spaces" without boxing them off.

I really don't see that air tight rating should matter. You are going to prevent air that is otherwise being drawn into the same space from getting there. If it is a code issue it is mechanical code issue and not NEC.

You mention insulating the roof as well as insulating the ceiling. Seems pointless to insulate the ceiling to me. You are drawing same air that you are trying to insulate from through the ceiling.

I think the owner needs to find a different HVAC contractor, like one that has a grasp of some basic physics.
 
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