ERV duct sizing
I am deciding whether to use 4″ or 6″ ductwork for my fresh air inlet and stale air exhaust lines running between an ERV and the outdoors. The inlet line is a straight 8′ run and the exhaust is a 12′ run with two 45 degree elbows. Using a 6″ line would mean less air resistance in the duct, but it also means a much bigger hole in my thermal envelope (roughly 28 square inches per 6″ hole rather than 12 square inches per 4″ hole.) With such short duct runs, I am leaning towards going with 4″ ductwork. Or would there be any benefit to using 6″ ductwork and reducing it down to 4″ just before it exits the building?
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