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My AC contractor just brought some 8 and some 6 inch spiral pipe to install tomorrow. I do not trust him nor do I trust a single contractor out there, hence posting here to confirm. I am getting a 3 ton system, there are three rooms upstairs and 2 rooms and a dining room downstairs. Total is about 1800 sq ft. I am suspecting he wants to use the 6" spiral (all spiral will be exposed) to server the hallway and one room upstairs (total about 400 sq ft) but to me it seems insufficient. Of course, he has every reason to lie and downsize me to save money. Can a 6" spiral pipe support enough air flow to serve 400 sq ft? Also, if you know of a spiral pipe online calculator, please share, I have not been able to find one.

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From my experience when I put duct in my house, a 6-inch duct will serve a small room...100-120 sqft. You can run two 6-inch ducts from an 8-inch duct. –  Edwin Dec 7 '13 at 9:01

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