'what are the advantages of using metal over commercial flex?
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ME: 1. 8" high metal trunkline ducts give you more headroom. 2. Metal rectangular looks neater and more professional-same with branch ducts. 3. Using metal ducts, you dont have to be concerned with the ducts blowing off or sagging. 4. Flex might not meet local code., except for the final 3' of branch duct run to the register.
'Also, is it worth the cost to go from a 10 to 12 SEER??
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ME: Depends on how extended your cooling season is, if you use your cooling alot, and if youre planning on staying in the house for awhile. Generally speaking , it is better to go with a 12 over a 10 seer because a 12 seer unit will run lower discharge pressures and 'should' make the compressor last longer. Plus, when you go to a 12 eer, most (if not all) manufacturers put a Scroll compressor in the unit which are dependable, quieter, and come with a 10 year warranty versus a 5 year warranty on a 10 seer compressor. Pretty soon, the minimum seer standard is going to be 13 just so you know.