Wrapped Plenums in Hot Attics (David and Charlie - chime in)

Do you guys ever advocate wrapping the exterior of supply plenums with batt insulation?

This one year warranty inspection has had issues with condensation (4 story, single system, three zone, no variable blower or bypass duct/barometric damper observed) lot’s of staining on the decking below. The builder has “addressed” the issue by adjusting slope of the plenums, installing a pan which extends past the plenums (new pan has rust staining) and wrapping the plenums with fiberglass batts.

I always considered this a “band-aid” solution for the symptom that masks an underlying problem (e.g., damaged / displaced insulation board inside the plenum, improper configuration of the system, etc.) rather than a proper fix. In my experience the fiberglass traps moisture against the outside of the plenum and promotes rust.

I’m interested in your expert opinions.

To answer your question!!! No Batt insulation is not intended to be used as plenum or duct type insulation. The metal plenum is normally insulated on the interior side with glued on insulation. Many plenums are constructed with a duct board that is just a solid fiber glass type material. If metal plenums are present one can normally tap on the side of the plenum to determine if insulation is on the inside.

I would think if the builder was trying to use a Batt insulation to cover the fact that the plenum was improperly insulated from the git go.

That pic you posted is a mess.

Chuck to change the subject a bit have you ever performed IR work around Houston area for a roofing company by the name of CentiMark? just curious

Thanks for your insights Charlie.

On the IR question: No. But they ask for bids with some frequency. I also get asked by another IR company if I can do IR roof inspections roofs that they bid for, which always seem to match what CentiMark has asked me to bid on. Sounds like they cast their net pretty wide seeking bids. Once they do this a couple of times, I quit sending real proposals and just quote a price - a high one.

I did not submit a bid to them I did a inspection on a roof they installed in Okla. The building owner wanted another set of eyes on their job before they paid them for the work. I was not impressed with their craftsmanship.

BTW Excessive sweating in the plenum can also be created by an improper super heat adjustment on the Refrigerant charge