flexible duct work

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  #1  
Old 08-29-02, 01:20 PM
jrv702
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flexible duct work

I was wondering what parts I need to install new flexible duct work to replace galvanized? Do I need ring clamps to attach it to the vent opening in both the floor and heating unit to keep it in place? Do I just use the mastic compound to seal it off and it should be good from there. I have forced are heat/ac. Any advice is appreciated. Thanks jrv.
 
  #2  
Old 08-29-02, 02:37 PM
bigjohn
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I understand that you want to replace sheet metal duct with flex? Is that correct? If so, I advise against it. Flex duct has significantly more resistance to airflow than sheet metal does. You'll lose a lot of your airflow unless you resize using a friction chart for flex duct. To answer your question about how to connect, you can buy long [48"] ty-wraps that are made for ciinching down flex duct. You also have to use a special tool that cinches them down tight. The tool isn't expensive. I usually attach flex duct by drilling some self tapping screws and small washers against the end of the metal spiral first. IOW- slip the inner core of the duct duct over the fitting, shoot the screws around the perimeter of the end of the wire spiral and then put on a couple ty-wraps. Then slide the insuation into place and ty-wrap it down. The I shoot expanding foam into and around the end of the duct. It's messy but will seal better than mastic. Sometimes times before shooting the mastic. I'll form the area in with heavy cardboard. I usually only use flex on mobile homes.
 
  #3  
Old 08-30-02, 01:46 PM
jrv702
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duct work

I have to replace the old galvavnize duct work currently in place. If I shrink the size of the tubes from the furnace to the floor vents (ie. 8"-6") will that produce more heat/ac that comes out of the vents or will it be reduced? Then use the mastic compound or would you advice something else to seal the work?
 
  #4  
Old 08-30-02, 02:55 PM
bigjohn
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I should have been more clear. If you replace what you have now with the same size flex duct, you will have less air flow. In order to get the same airflow you have now with flex duct you will have increase the size of the duct, not decrease it.
 
 

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