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  1. #1

    replace ducts or not?

    I have a heat pump that is 22 years old. It is dead and would be expensive to repair.
    The ducts were already in the house running a furnace before I got the heat pump. (The ducts would have to be 30 plus years old)
    My house has 1500 square feet and 10 supply vemts.
    My return vent is 20x30
    Some insulation on the ducts needs to be rewrapped. Probably a roll and a halfs worth of insulation replaced.
    I am getting quotes for a new all electric heat pump. It will be a 3 ton 13 seer split system.
    A couple of places want to replace all of the existing metal duct work with new metal ductwork.
    Their reason is because the ducts are all 4 inch pipes going to 2x12 register boots.
    One place says that they will have to make the return vent larger because new units require larger ducts and returns.
    One place says they can wait and see if it works and replace the return if it doesnt't measure good after it is installed.
    Does anyone know whether these people are just making this stuff up?
    No other quotes mentioned the ducts other than making it fit the new system and rewrapping the insulation where it is needed.
    I figure the system may have to work harder with small ducts but I could buy two almost for what the ducts are going to cost.
    Final question... carrier or trane? which to pick

    Thanks

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    10-4" supply runs isn't nearly enough for a 3 ton.
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    How many times must one fix something before it is fixed?

  3. #3
    Would 10 supply runs that were 8 inch be enough? And what about the return vent size? What would happen if they are too small if anything.

  4. #4
    Join Date
    Jan 2004
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    10-8" would be enough.

    If the return is under sized, then it will be starved for air.
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  5. #5
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
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    Correctly sized sealed and installed new duct will far outperform old undersized leaky duct. I've seen many old duct systems leak 50-60% of the heated/cooled air before it enters the house.

  6. #6
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
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    Quote Originally Posted by jtrammel View Post
    Correctly sized sealed and installed new duct will far outperform old undersized leaky duct. I've seen many old duct systems leak 50-60% of the heated/cooled air before it enters the house.
    +1. You may find that a 2 ton unit is all that you need once the ductwork is fixed. 100% of 2 tons = 66% of 3 tons...

  7. #7
    Join Date
    May 2004
    Location
    south louisiana
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    3,163
    +2
    velocity of air is higher with cooling than heating.
    you don't want screaming ducts..LOL!

    cost is high to replace ducts, its a lot of work
    new plenum, new ducts, supply boxes & grills
    plus time to cut new holes for new supply boxes & grills.


    size of ducts & number of ducts is determined by size of room
    to be cooled.

    lots of 30+ year old hard duct systems still around. Most leak
    quite a bit, but the size of the ducts is the other part of the problem you have.

    I know some folks are kinda funny about flex duct, but it is less time to
    install. Properly installed, mastic sealed, duct strapped flex systems work well.
    but..they have to be straight tight runs with gradual turns, not just octopus duct
    systems.

    there is some validity to the statements you posted. they aren't just making
    stuff up. just not wanting to lose the sale over the ductwork issue.
    lots of companies don't look at duct systems at all, so at least
    they are.

    why not higher SEER? 13 is the minimum efficiency made these days.
    I'd look at 15 seer with VS air handler unit.

    change the duct system, mastic seal all ducts, plenum connections & R/A,
    increase efficiency and 2 ton might be right for you.

    where are you located?

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

  8. #8
    I am in central Alabama. I haven't really priced anything above a 13 Seer. I am on a budget due to some other remodeling and wasn't really planning on a new heat pump right now, much less the new ducts. I have a crawl space so animals could possibly get to the flex ducts. I will ask them about them though.

  9. #9
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,163
    oh ...didn't realize this was in a crawlspace
    flex & armadillos, possums isn't a good thing.
    they dig into the flex to get warm.
    that is probably why your duct wrap is comming off.

    can you close off crawlspace with wire fencing
    with small 2"x4" openings? that is what I used @ my Mom's trailer to
    keep critters out. cut the 4' fencing in half width wise, & 2' was the
    average height I had to close in. worked well.

    only if critters had no access to get into crawlspace would I use flex.
    even then..it has to be strapped off ground.

    best of luck

    for some reason..I always envision ducts in attics..cause I see so
    much of it I guess.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  10. #10
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,186
    A 14-15 SEER unit isn't that much more expensive than the 13 SEER. It's when you get into the the 2 stage/16SEER units when the price jumps.

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