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*Minimum* Duct Length for ERV Intake?

jamesboris | Posted in Mechanicals on

I’m installing a Panasonic Whispercomfort ERV in a bedroom wall stud cavity, furred out to 7″ D. The runs are simple — 4″ vertical flex followed by a *rigid* 90 elbow through the wall (I’d rather (2) 45’s, but don’t want the chase to project too far into the room). The sealing and workmanship will be high quality.

But on the design side… Is there a *minimum* length of duct I need on the intake side for it to work best? One Panasonic tech support guy said no; the other said I need to have 3′ of duct to have enough static pressure. Who’s right?

In case Guy #2 is right… well, it’s said that a single 90 elbow counts as 10-15′ of duct… so can I just terminate immediately out of the ERV? Maybe after 1′ of flex for practical purposes.

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