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We're in an attic in Phoenix, directly over the closet that holds the air handler. With a flashlight and smoke pencil, which makes the air stream visible, we watch hot attic air being sucked into return duct fittings and down the interior partition walls into the air-handler's platform plenum below. Later, while inspecting the crawlspace, we see chilled air leaking out of supply branch lines where they exit the trunk line. With attic temperatures averaging more than 20°F higher than outdoor temperatures it's no wonder the occupants are disappointed with their air conditioner's performance. After all, it's trying to cool 120°F attic air while losing cooled air to the crawlspace. The preceding scenario is unfortunately the rule rather than the exception. And