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Need help with our ductwork decision

user-5626012 | Posted in Energy Efficiency and Durability on

I contacted a reputable contractor to come do a duct test and take a look at our attic insulation. The ducts are very leaky and most of them are the old grey kind and some are not in the best shape. One even was missing all the inner plastic and all you could see was the metal ribbing and fiberglass.

The house is around 2,050 sq. ft., and the blower door showed about 2600 cfm at 50. The auditor showed me all the areas I need to seal up from the inside and took picture of the worst areas in the attic like the chimney and bathroom soffits. He said that the duct board trunk has started delaminating in places but that it could still be used if they sealed it better with mastic. He also mentioned that not all the flex is in bad shape but all the connections are leaking.

Another issue at least in my opinion are the metal boots. They are insulated on the inside and I’ve been up close to one and it smelled. There are stains around the registers so they definitely have some condisation issues. He mentioned with proper connections and the added insulation should stop the condensation but I’m not sure if we should keep them.

My question would be: should we just replace some flex and patch what we can and then insulate or replace everything? They quoted $350 after our rebates from the power company to replace the broken flex and seal every connection and the trunk. The cost to replace everything and then replace with flex and distribution boxed would be $3900-4500.

We plan on living here for awhile, so just not sure what choice to make, or if there is an option in between that might work better.

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  1. GBA Editor
    Martin Holladay | | #1

    It's hard to assess the condition of your ducts based on your description. Some photos might help -- but ultimately, this is a judgment call. It's hard to make that judgment without visiting your attic.

    Obviously, there is a large cost difference between the two approaches, so your decision may hinge on how much cash you have on hand.

  2. user-5626012 | | #2

    This shows a good bit of what we're dealing with.

  3. user-5626012 | | #3

    I've decided to replace the broken duct myself and will have the ability to inspect the inside of the duct board trunk then to see if it's worth keeping.

  4. BobHr | | #4

    you house is the perfect example of why I hate flex. The top picture on the left side of the trunk are 2 flex duct. One has a "S" bend because the flex wasnt cut to the the proper length. The other 1 turns 90 degrees and runs along side the trunk. They didnt use a metal elbow and why was the take off in the location. The bottom picture show flex and none of runs in a straight line.

    Trunks should run from one end of the attic to the other. Flex should come straight off the sides and run in a straight line to the register. Doing it this way give you the best air flow and allows the flex to sit between the ceiling joists. Blown in insulation can them be piled up over the top of the flex and its insulation.

    I also see you have a cathedral ceiling in the bathroom. The fiberglass batt insulation that you can see has very little R value installed like that.

  5. user-5626012 | | #5

    Robert, thanks for the observations. As for the vertical section of the vaulted area, what would work better there? I was thinking Roxul might be a good choice since it friction fits much better. That is an area I can easily get to but not the ceiling to roof section. I think i'll have to live with the fiberglass there but there is room to add additional blown fiberglass or cellulose on top.

  6. charlie_sullivan | | #6

    The issue with the vertical fiberglass is not so much that fiberglass is bad, but that it, or mineral wool, works best with an air barrier on each side. You could simply staple up housewrap over it, or use thin plywood or drywall. Just don't use a vapor barrier like polyethylene.

    The insulation of the sloped roof is a bigger challenge, for many reasons. See

    I don't think we know enough details to really advise on this, but for $5k you could install a mini-split and avoid the need for ducts in the attic at all.

  7. user-5626012 | | #7

    I would have to take some additional pictures of that area, there is a good bit of space between the vaulted rafters and the roof rafters but not enough for someone to get in there. To make matters worse there is a skylight and can light in that area as well. As for the mini-split method, that is just not in the cards right now. The house has a brand new a/c system, they just didn't bother to fix anything with the duct work.

  8. user-5626012 | | #8

    Here are some additional pictures. The first one is the slope of the vaulted room. It has fiberglass that seems alright but towards the peak there is rodent droppings that might need to be replaced. Also, I believe the duct right below might have also been damaged by rodents.

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