Solid Duct vs. Flex Duct, should I replace old leaky ducts with Flex Duct?


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Old 05-23-11, 04:22 AM
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Solid Duct vs. Flex Duct, should I replace old leaky ducts with Flex Duct?

Sorry I just could not find any activity really in the Duct area. So at least maybe someone will see this before it gets moved. Just wondering as I had a couple old schoolers tell me never to get rid of my solid duct. And If you guys agree with FLex duct, then which kind/brand?
 
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Old 05-23-11, 07:11 AM
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really depends on the condition of the ducts, leakage , if there wrapped with asbestos, easily accessed, Given the choice I would upgrade to flex ducts that are properly sealed and laid out to maximize efficiency.
 
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Old 05-23-11, 05:55 PM
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I'm going to disagree with Brian. I often take out flex & replace it with metal, properly sealed & insulated. Size for size, metal will carry more air due to less friction loss. The wire helix in flex creates a huge amount of resistance to air flow. Flex has it's place & that place is for short runs of no more than 5 feet for sound attenuation.
 
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Old 05-23-11, 09:15 PM
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Questions moved to top in this post as I realized I rambled too long....

(1)But the big question would be: If i was to rewrap, what product to use? Do they make a prefab'd sleeve type? Is is cheaper just to take some R-13 and wrap around? Whats the best proceedure? Run (2) longways and tape a seam lenthwise on both sides? What works best if I decide to rewrap.?

(2)With regard to Flex duct, I am concerned about the poor interior construction I have seen in home depot shelf brand. Lowes carries a black on that looks pretty tough on the outside.. So which brand if Going flex?

You guys both have excellent points. I understand I could more efficiently route my attic with the flex. It just seems like an easy "quikfix".. I did not really give consideration to the issue with the resistance. One part of me wants to immediately dismiss and equate to the auto dealer telling me my gas mileage on my new car sucks because of dirty paint causing air resistance.. But I get it. There is always the issue with the fact that areas may compress too. But still I could use a larger size up all over and be sure not issues there. Should not really affect the R factor I would think. Good point I had not considered.! I just hate the thought of going up there to re-wrap everything! But I am also thinking it probably would turn out easier and I would regreat trying to demo the solid. I do have a couple of runs that were simply not big enough in this 1960 home and the room gets no air. I have checked the main box baffle, tweaked all other trunk output flaps/baffles (not sure what to call them). Just no go to that room. I cant help but wonder if I dont have a massive leak I have missed (which is possible).
 
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Old 05-24-11, 03:27 AM
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flex has to be sized bigger than rigid round duct to flow the same cfm. To wrap current rigid duct I would use what we call foil-back insulation. Wrap length wise depending on size of duct and staple if possible and definitely foil tape to seal also. If you are going to redo the ducts if flex then go with Hart/Cooley and the highest r value you can buy.
 
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Old 05-24-11, 08:15 AM
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I'm with Grady, can't imagine a situation where I'd replace rigid with flex
 
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Old 05-24-11, 09:46 AM
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as I said it really comes down to the condition of the rigid, and how much money you want to spend. If you got the money to refurbish or replace the rigid of course it will be better but on a monetary situation new properly sealed and laid out flex will give you your moneys worth.
 
 

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