How to insulate old metal ductwork in attic? - Family Handyman DIY Home Forum
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How to insulate old metal ductwork in attic?

Posted: 20 Dec 2010 10:50 PM By: Mobea Replies: 5

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  • How to insulate old metal ductwork in attic?

    I am a disabled woman who cannot afford to hire someone so I...WILL do this MYSELF!!! LOL Someone told me that it isn't that important if the duct work had any insulation on it as long as it isn't leaking..That just doesn't sound/feel right to me.I have the square metal type of duct work that is about 10 or 11 yrs old. Isn't there some type of insulation that I can wrap around it and use some of that shiny duct tape at each joint to secure it? What is the proper way to do this?

    Thanks for you help,

    MobeaB

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  • Re: How to insulate old metal ductwork in attic?

    Your common sense wins.  Even if the metal duct work doesn't leak, the metal will lose heat by radiation and conduction (wherever the metal contacts another material).  Insulation will help minimize these types of heat losses.  Stores like Home Depot and Lowes sell duct or pipe wrap inulation and it can be secured with dict tape.

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  • Re: How to insulate old metal ductwork in attic?

    As long as you know the size of the duct and how long it is you'll be able to get the right insulation for it.  Also make sure to get the correct tape.  Regular duct tape will work, but it isn't ideal.  The people at the stores will be able to help you with that.  You could even do the whole project in stages as your money allows.
    Be careful and good luck!

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  • Re: How to insulate old metal ductwork in attic?

    I just bought an older farmhouse that I am remodeling. I have the same ductwork in the attic for the second floor rooms. They were exposed to the air and I expect that the previous owners were getting pretty cold air by the time it reached the rooms. I live in Minnesota. I had very good results with making sure the joints and seems of the ductwork were not leaking and then added an R-30 over the entire attic floor covering the ductwork. Then I added another R-30 over the top of that. Make sure you do not block any airflow from the soffets into the attic area and make sure you have enough roof vents. Some of those old houses do not have airflow in the soffits and in that case still make sure you have roof vents at least on two opposing sides of the roof. You will get some airflow that way.

    P/S I believe some of those old houses used thin asbestos for insulating those runs. Be careful and use masks when removing or working with that old material.

     

     

     

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  • Re: How to insulate old metal ductwork in attic?

    I am an insulator for Local 27 in Kansas City, MO, this is a fairly simple project.  Your local hardware stores should sell everything you will need, although it can be rather expensive.  Home Depot carries Owens Corning duct wrap and you will need some 3' wide or wider foil tape, not duct tape.  Measure the distance around the duct for square or rectangle duct measure two sides(L and W) and double it then add 8' to 10' for lap.  For round duct measure around the duct and add 8' for lap.  We use a outward clinching staple gun when installing but you can get away without using one.  Wrap the duct wrap around the duct, tape one side to the duct, and then pull the other side around and tape it down make sure to use a squeegee of some kind or the tape will probably come loose.  Tape the seam and the butt joints squeegee the tape and DONE!!!

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  • Re: How to insulate old metal ductwork in attic?

    You say that your duct work is 10-11 yrs old and in the attic, it is possible that your duct work is insulated already from the inside with a duct liner that is pin spotted. Some residential companies do that instead of wrapping the duct on the outside, but it's fairly common on commercial systems. Usually the R-value is on the lower side if a liner is used in residential ducts. Some jurisdictions now have codes in place that require a certain R-value ( R-6 in some places) for duct work in a unconditioned attic for new homes, therefore, getting that R-value out of a liner would be difficult when you're dealing with residential ducts because of increasing the size of your duct for CFM requirements and of course taking up more space.   Just some info you may find helpful.

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