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  1. #1
    Join Date
    May 2009
    Location
    California
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    14

    Need replacement advice on dual unit

    Hello, I have been reading on here for a week or so and my head is spinning. I was trying to educate myself a bit so I could ask the right questions to the companies giving me bids for a new dual unit. Decided to post a thread and hoped someone could turn me in the right direction. I have a 20 year old 5 ton 'Day n Night' dual unit (which I assume means the AC and furnace are in the same unit) that sits outside at the end of the house. The AC compressor went out last September but the furnace worked all winter. I decided to replace the complete unit (right or wrong?) because of its age.
    I've had 3 bids, all expensive, all from large respectable companies suggesting similar solutions: Change the 2-16" return ducts to 18" and an Amer Standard 'Triumph' 4YCY4 unit. Why I am puzzled now is that after reading on this site, none of the companies offered to do any load calculations. They just looked at my 2700 sq ft home, saw the old unit was a 5 ton unit and said I needed larger return ducts to balance the return air and the supply air. I'm not saying they are wrong but is this how a standard estimate is given?
    Any advice is much appreciated.

  2. #2
    Join Date
    May 2009
    Location
    California
    Posts
    14
    Anybody familiar with that Amer Stand unit or any suggestions?

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,125
    Many companies do guess at what is needed.

    Shouldn't be that way. But it often times is.

    Your current return system may be undersized. And the two returns may ned to be increased to 2-18" ducts. Are they also increasing the return grilles?
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  4. #4
    Join Date
    May 2009
    Location
    California
    Posts
    14
    They did say they would increase the return grilles size. The 2 return grilles are in the hallway ceiling. The trusses in the ceiling are on 16" center. The present grilles are 16" x 25" and they said they would have to calculate how much larger. They said maybe 16" x 30" but wasn't sure.

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,125
    If they're filter grilles. You'll need larger then 2-16x30 grilles
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  6. #6
    Join Date
    May 2009
    Location
    California
    Posts
    14
    They are filter grilles. He was saying something about needing to pull about 1000 (cfm?) per duct. Plus the 2 old ducts lay in the attic and go into 1-16" wall chase that must be enlarged, or, he said they could possibly knock out the existing 16" duct (in the chase) and drop the 2 new 18" down in a new enlarged wall chase.

  7. #7
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,989
    Quote Originally Posted by tommyncal View Post
    Hello, I have been reading on here for a week or so and my head is spinning. I was trying to educate myself a bit so I could ask the right questions to the companies giving me bids for a new dual unit.

    Decided to post a thread and hoped someone could turn me in the right direction. I have a 20 year old 5 ton 'Day n Night' dual unit (which I assume means the AC and furnace are in the same unit) that sits outside at the end of the house.

    The AC compressor went out last September but the furnace worked all winter. I decided to replace the complete unit (right or wrong?) because of its age.

    I've had 3 bids, all expensive, all from large respectable companies suggesting similar solutions: Change the 2-16" return ducts to 18" and an Amer Standard 'Triumph' 4YCY4 unit. Why I am puzzled now is that after reading on this site, none of the companies offered to do any load calculations.

    They just looked at my 2700 sq ft home, saw the old unit was a 5 ton unit and said I needed larger return ducts to balance the return air and the supply air. I'm not saying they are wrong but is this how a standard estimate is given?
    Any advice is much appreciated.
    In CA, what major city do you live in or near?

    In most of CA, five ton seems like an awful lot of tonnage for 2700-sf
    Is it all windows & doors?

    Have someone check out your home (blower door test) locate excessive air infiltration & eliminate it; address any window radiant heat problems & lack of insulation.

    Then get a load calc done,& size accordingly; do the same for heating mode.
    Bet you could get it down to at least 3 or 3.5-ton A/C or Heat Pump.
    Old unit probably didn't have airflow enough for anywhere near 5-ton.

    We have 2-ton cooling 2400-sf homes here in 104-F Heat Index.
    - Darrell
    Last edited by udarrell; 05-14-2009 at 01:27 PM. Reason: Old unit -airflow enough for anywhere near 5-ton

  8. #8
    Join Date
    May 2009
    Location
    California
    Posts
    14
    Quote Originally Posted by udarrell View Post
    In CA, what major city do you live in or near?

    In most of CA, five ton seems like an awful lot of tonnage for 2700-sf
    Is it all windows & doors?

    Have someone check out your home (blower door test) locate excessive air infiltration & eliminate it; address any window radiant heat problems & lack of insulation.

    Then get a load calc done,& size accordingly; do the same for heating mode.
    Bet you could get it down to at least 3 or 3.5-ton A/C or Heat Pump.
    Old unit probably didn't have airflow enough for anywhere near 5-ton.

    We have 2-ton cooling 2400-sf homes here in 104-F Heat Index.
    - Darrell
    I'm near Sacramento where it does get into the 100 degree temps during summer. The house does have some large open windows without coverings (which we like). I am working out the door leaks and such. With 2-16" return ducts flowing into 1-16" cramped wall chase duct and 2-16" x 25" filtered grilles, I'm sure the old 5 ton unit wasn't very efficient.

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