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Community and Q&A

Insulated plenum in conditioned space?

Kevin_D | Posted in Energy Efficiency and Durability on

Good evening!

My wife and I are completing a large addition. We have tried to follow many GBA tips for building a good and energy efficient house.

We are having a problem with the HVAC contractor.

When he bid the job he said “No problem” to everything, but then in the middle he kept trying to cut corners.

He did fix some things in the middle when I complained, but now he’s done and it’s still sub-par.

We did all new ducts and systems. He bid it as a typical install in an unconditioned space.
We did spray foam at the roof and made the attic a conditioned space halfway through the job. We blocked the ridge and eve venting and sprayed.

His air leakage is above 7% on the brand new ducting! New ducting should be below 6%, but he says he doesn’t have to since it’s in a conditioned space.

He didn’t insulate the plenum. He says he doesn’t have to, since it’s in a conditioned space.

I understand the per code, doing the minimum he doesn’t have to insulate the plenum.

Is there any value in insisting he insulate the plenum? [I’ve found some documentation to insist he tries to fix the air leakage (although I won’t turn down more ammo!).]

To me, it seems logical to insulate the plenum. I’ve been in the attic and it’s still warmer than the house. I’d guess 10 degrees or so.

I’d also like to reiterate that we paid for a full install in an unconditioned space. I’m not trying to make him do extra work for free.
Also, we paid a good amount. There were bids that came in decently lower. We paid for “quality”, or so we thought.

I appreciate your help!

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  1. GBA Editor
    Martin Holladay | | #1

    If your HVAC equipment and ductwork are all in conditioned space, there isn't any evidence that insulating your plenums or reducing duct leakage from 7% to 6% will save you any energy.

    By the way, there is some evidence that a little bit of duct leakage can be a good thing for an unvented conditioned attic, especially if your contractor used open-cell spray foam under your roof sheathing.

  2. user-2890856 | | #2

    Martin has made the most relevant point and that is sound advice . As for the contractual agreement , you spent your money the way you did for a reason and the fact that this man has tried to use your investment for his financial gain is not acceptable . Tell him to install the job he bid or credit you some monies , not that plenum insulation and labor would amount to loads it is a principle issue .

  3. Kevin_D | | #3

    Thank you so much for your answers!

    I'm actually glad that's the case. It's probably easier to get money off than to get them to do the work! The attic is closed in now, so it would be a huge pain!

    The foam is closed cell btw.

    The article I had found that encouraged good duct sealing was this one:

    Thanks again! This will make it a lot easier!

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