Insulation on ducts within conditioned space, condensation?
Hi, I am in the planning phase of a remodel of a 2 story house in the San Francisco Bay Area, Zone 3c. The ducted multi-split system’s duct work will be located within conditioned space, and I plan on a tight install mostly with rigid ducting except for the final flex duct runs to the registers. The issue is in the 1st floor where I am attempting to run most of the ducts within ceiling joist bays (2 x 8″ joists, so 7-1/4″ actual) so I don’t lose head room. The joists also sit on a few beams that have to be crossed, so there we are also constrained by the same 2 x 8″ joist bay height.
The HVAC designer who lives in another climate zone has made a recommendation to insulate these ducts due to concerns of condensation even though they are within conditioned space. The thinnest duct sleeve insulation I can find is R-4.2 at 1-1/4″ per side for a total of 2-1/2″. This limits ducts to 4-3/4″ in height which won’t get the job done.
If we ensure the joist bays where the ducts run are well air sealed, particularly at the rim joists, will condensation be a real problem? Asked another way, can I get away without duct insulation? If insulation is important, are there any other solutions out there?
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