Return Plenum Penetration

Originally Posted By: Robert Wade
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[ Image: http://www.nachi.org/bbsystem/usrimages/D/DCP019711.JPG ]


What do you think?

This is a joist-panned cold air return fabricated from melamine coated tempered masonite. Masonite forms all six sides of the plenum. (The duct running right to left in the picture is a dryer vent and is not part of the question.) The steel duct coming over your right shoulder is a return from a room. There is another connection farther down that cannot be seen. At the far end the masonite plenum is connect to a steel plenum hanging below the joists. All joints in the melamine are caulked.

The white pipe to the left is part of an installed central vacuum system which continues through the plenum and exits at the other end of the plenum. The wires are low-voltage control (12 VAC) for the central vacuum system. There are no wire splices inside the plenum.

The cross-section of the masonite plenum is 12" x 12" and the two ducts connected are 6" rounds.


Originally Posted By: Jay Moge
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not sure i understand what you question is? about the masonite? icon_confused.gif


Originally Posted By: dandersen
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Utilities are not allowed in an HVAC Plenum.


The HVAC gets first crack at location, all other utilities must go around.


Originally Posted By: apfaff
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Looks like a creative solution to adding ducts were needed after the fact. I would just note it is not standard installation. In a perfect world it is not right but what problem could come from it?



Aaron Pfaff


http://www.dedicatedhomeservices.com/


http://www.independentinspectors.org/wisconsin.html

Originally Posted By: Robert Wade
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Thank you, All;


There were multiple questions, but I didn’t want to lead the witness so I just described the installation.


1) Would you consider tempered masonite an acceptable (not ideal) alternative for the return plenum? What is the reference, if any?

2) I knew industrial HVAC doesn't allow penetration of ductwork by other utllities but wasn't sure about residential.

3) What about low-voltage wire in ductwork. I see ads for plenum-rated wiring in electrical supply catalogues. That implies to me that under certain circumstance it is permissible to have certain wiring, at least, in ductwork.

4) One problem I could see arising would be if the central vacuum pipe were to separate within the return it would suck return air out of the HVAC system. Not sure what effect that would have, but it wouldn't be good.


Originally Posted By: dandersen
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Quote:
C. Inspectors are NOT required to offer:
2. or perform engineering services.


If they don't allow it in commercial application, why would it be ok in a residential application? ![icon_biggrin.gif](upload://iKNGSw3qcRIEmXySa8gItY6Gczg.gif)