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  1. #1
    Join Date
    Sep 2004
    Posts
    28

    Insulating ducts

    Hi all,
    What do you think about insulating duct work in a house? So far I have talked to two people and of course received two differnt answers. One said it is workwhile to inulate the ducts as it will save money. The other said since the ducts are mor or less in conditioned space it is not really worht it. The house is a two story with basement. The ducts are all in the basement which is half finished. It is always comfortable in the basement as it is always within a few degrees of the thermostat setting. So what say you guys. Worth insulating or not?
    Thanks.

  2. #2
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
    Posts
    5,010
    Nope.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  3. #3
    Join Date
    Nov 2006
    Location
    Athens, Ohio
    Posts
    1,783
    There is no appreciable heat loss or gain when the ducts are in the conditioned space.
    So the answer is: It is not worth insulating the ducts.

  4. #4
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,741
    not worth it imo.
    the other problem is unless the ducts are tightly insulated moisture will get under the insulation and make a big mess. with ducts already installed getting a good tight seal on the insulation is impossible.

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,923
    In the unfinished area yes, in the finished conditioned area no.
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    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  6. #6
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,170
    Quote Originally Posted by t527ed View Post
    not worth it imo.
    the other problem is unless the ducts are tightly insulated moisture will get under the insulation and make a big mess. with ducts already installed getting a good tight seal on the insulation is impossible.
    do you mean unless the ducts are tightly sealed that the moisture will get(form) under insulation?

    I don't get the basement stuff, read about it, but haven't
    dealt with it. no basements in my area.

    but wouldn't you mastic seal the ducts, so conditioned air won't leak out?

    and as you want to keep air as close to temp supplied by system as
    it is at delivery into each room...isn't insulating ducts the best way to
    do this?

    just asking. the few houses I've been in with ducts in basements
    were sealed & insulated.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  7. #7
    Join Date
    Jan 2008
    Location
    Texas
    Posts
    1,786
    When I lived in Missouri none of the ducts in the basements that I seen were insulated.

  8. #8
    Join Date
    Dec 2005
    Location
    Cincinnati, Oh
    Posts
    5,010
    Quote Originally Posted by energy_rater_La View Post
    do you mean unless the ducts are tightly sealed that the moisture will get(form) under insulation?

    I don't get the basement stuff, read about it, but haven't
    dealt with it. no basements in my area.

    but wouldn't you mastic seal the ducts, so conditioned air won't leak out?

    and as you want to keep air as close to temp supplied by system as
    it is at delivery into each room...isn't insulating ducts the best way to
    do this?

    just asking. the few houses I've been in with ducts in basements
    were sealed & insulated.
    Imagine you had a room that you didn't heat or cool in the house.
    Lets say you wanted to close the register to accomplish this.
    Sounds good.
    Except that we're talking about spending quite a good chunk of cash on it, not closing a register.

    The problem with insulating ductwork in a basement, is what are you going to lose?
    The duct will lose some heat to the basement. Yet, the basement is inside the envelope. So are you really "losing" the heat, or are you slightly heating the basement, lowering the heatloss through the floor to the basement?

    Although I disagree with beenthere, I don't disagree with the science. I disagree with the practicality. I see a very minimum savings that would take a very long time to pay back.

    I think the money spent on the duct insulation would be better spent on air sealing, more attic insulation, or a case of beer.


    As a side note, we used to be in a program that payed to seal supply duct in basements.
    The problem was that the first air conditioner season the ducts would sweat.
    Now you have to fix that issue. Which is a dehumidifier. Or a register on the duct, essentially negating the entire supply duct sealing.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  9. #9
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,741
    Quote Originally Posted by energy_rater_La View Post
    do you mean unless the ducts are tightly sealed that the moisture will get(form) under insulation?

    I don't get the basement stuff, read about it, but haven't
    dealt with it. no basements in my area.

    but wouldn't you mastic seal the ducts, so conditioned air won't leak out?

    and as you want to keep air as close to temp supplied by system as
    it is at delivery into each room...isn't insulating ducts the best way to
    do this?

    just asking. the few houses I've been in with ducts in basements
    were sealed & insulated.

    what i mean is unless you get a good tight seal on the insulation it will have areas where moist air can get to the cold ducts and condense. if the ducts are insulated before they are installed it won't be a problem. to try insulating an existing basement duct system would be more trouble than its worth.

  10. #10
    Join Date
    Sep 2004
    Posts
    28
    Thanks, looks like the pro who told me it was not worth it was on the money. I always hate it when I get estimates and they vary wildly. In this case polar opposites. Here it was unanimous. Thanks again.

  11. #11
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,170
    ok, the gap between duct & insulation condensating. got it!

    with ductwork like house better to air seal before insulating.
    or in basements air seal & let heat from uninsulated duct
    contribute to heating basement.

    in my way of thinking..air seal insulate and dedicate a duct to basement
    wouldn't be the way to do it. hmmm food for thought.

    mross, bids seem to always vary. that is why running them by pros here is a good
    idea.

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

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