Thread: Commercial Ductwork

Inspected a school recently to assist in locating what they thought was a roof leak (using IR). It appears that the leak is not from the roof but rather from condensate forming around ducts. I noticed that some of the ducts are insulated from the exterior and some appear to be insulated from the interior of the duct (similar to residential trunk-lines and plenums using insulating duct board).
My question for the group is this...

Are metal ducts required or is the insulating duct materials allowed in a drop ceiling area? I can see both pros and cons to either materials but would like a gut check from the group?

Similar Threads:

• Conduit for exterior lighting - commercial
• Commercial Exterior Lighting
• Commercial: Stucco interface with flat work
• Commercial zone system,

Originally Posted by Jeff Zehnder

Inspected a school recently to assist in locating what they thought was a roof leak (using IR). It appears that the leak is not from the roof but rather from condensate forming around ducts. I noticed that some of the ducts are insulated from the exterior and some appear to be insulated from the interior of the duct (similar to residential trunk-lines and plenums using insulating duct board).
My question for the group is this...

Are metal ducts required or is the insulating duct materials allowed in a drop ceiling area? I can see both pros and cons to either materials but would like a gut check from the group?

Not sure I completely understand your question. However ductwrap and ductboard normally meet the flame and smoke spread ratings required by the fire marshall and are permitted in a dropped ceiling area.

Ductwork does not have to be metal construction.

Ron,

Appreciate your reply...
Yes part of my question was related to the use of duct board vs metal duck but the interesting thing is the metal duct is having issues with condensation dripping on ceiling tiles under the metal supports. I know that in some cases (hospitals) metal ducts must be used along with fire dampers but this is a school (built year ago and remodeled every few years) that has different generations of products that do not seem to behave well together.

The condensation in the duct is carry over from the evaporator coil.
The cause is usually high face velocity across the coil.

You should recommend further evaluation by an HVAC engineer.

Jeff,
Not able to look for actual reference now, but in the back of my mind I think that metal duct is required in commercial work. Insulated or not, interior or exterior insulated not the issue but metal duct is required. Not absolutely sure, just a fuzzy thought/memory.

You'd have to check your local Codes but metal duct may be required, typical in commercial. The condensation could be coming from a multitude of sources.
- from the system itself, getting pulled in from the coil or outside air, I've seen 'thought he knew what he was doing' make-up air ducts that essentially drew in the rain every time it rained.
- economizer may be an issue, make-up air duct set-up could be an issue
- could be ventilation issues in the dropped ceiling
- could be way too many holes in the dropped ceiling allowing too much occupancy space air into the ceiling
I would suggest approaching this with multiple people and disciplines. HVAC guy checks out system, maybe do a modified blower door type test on the dropped ceiling, assess any ceiling ventilation to the exterior - either legit or not.
Trying to look at it from one perspective may not provide the client with sufficient answers to resolve the problem, just more questions.

You don't have to use metal duct in commercial buildings. Not by code or by function. You can use gyp board if you want. I would recommend galvanized duct in most cases however.

Internally lined ducts are typically for niose and are usually within 10 to 15 feet of the unit they serve. Depending on the thickness of the liner, the ducts could be required to be wrapped also.