The only time you can consider the ducts as being in conditioned space is if the ducts and air handler are installed underneath the ceiling inside the thermal and air barrier of the envelope.
If the ducts are in an attic with continuous insulation at the roof deck is that considered conditioned space? No, however, when there is roof deck insulation the attic temperature will be much closer to the conditions within the conditioned space and that is already accounted for in the software. So there is a tremendous benefit from roof deck insulation even if the ducts are not able to be considered as within conditioned space. (NOTE: Because a radiant barrier requires a 1-1/2″ air space, when roof deck insulation is modeled uncheck the radiant barrier option.)
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