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  1. #1

    upgrading to larger unit

    Hi,I live in a 20 year old 1,800 sq. ft. 2 story house that currently has a single 2.5 ton unit(gas heat).I've been advised to go to a 3.5 ton unit (heat pump this time).My question is will all my duct work have to be replaced.I don't know the size of the returns but the upstairs has a 14x14 filter and downstairs has a 20x20 filter.Thanks.

  2. #2
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    only your installing contractor could give you an honest answer.

    I am not a bettin man but if I was, I would say that there is a good possiblity of maybe needing to replace the ductwork.
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  3. #3
    Join Date
    Mar 2007
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    Why are you going to a larger unit? Did the old unit cool OK? Did he do a load calculation? Did he measure air flow and static pressure on the old system?

    If I was a betting man, I would bet you will need to replace the ducts for a larger unit.
    Remember, Air Conditioning begins with AIR.

  4. #4
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    Jan 2004
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    Get another contractor.

    If I was a betting man, i'd bet your ductwork is already smaller then it should be for a 2.5 ton, let alone a 3.5 ton unit.
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  5. #5
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    I would bet that you would definately have to upgrade your duct work going from a 2.5 ton to a 3.5 ton that a whole ton more than you had and based on you having 2.5 ton before who's to say your existing duct work was or is sized for 2.5 tons ? and if there undersized for 2.5 tons imagine running with a 3.5 tons you would have to get your ear plugs on when you turn the AC on

  6. #6
    My unit won't cut off during the day,only at night when the outside temp. drops.The air is cold coming out but it won't bring the interior temp. down once it starts to rise.We keep the blinds shut and enter and exit the house quickly.The contractor said the unit was just too small for my house (1,800 sq. ft. colonial with original wooden windows).It was 91 today and we have it set on 75 and only got down to 78.He checked the pressure in the unit and it was good then did some calculations and came up with 3.2 tons needed and recomended a 3.5 ton unit.I didn't think to ask about the duct work being sufficient for the upgrade.I've got another company coming out Wednesday I'll be sure to ask about the duct work.

  7. #7
    Join Date
    Aug 2007
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    Quote Originally Posted by hrdhead View Post
    My unit won't cut off during the day,only at night when the outside temp. drops.The air is cold coming out but it won't bring the interior temp. down once it starts to rise.We keep the blinds shut and enter and exit the house quickly.The contractor said the unit was just too small for my house (1,800 sq. ft. colonial with original wooden windows).It was 91 today and we have it set on 75 and only got down to 78.He checked the pressure in the unit and it was good then did some calculations and came up with 3.2 tons needed and recomended a 3.5 ton unit.I didn't think to ask about the duct work being sufficient for the upgrade.I've got another company coming out Wednesday I'll be sure to ask about the duct work.
    Since it looks like he has already done the load calc and came up with 3.2 tons required, I would ask for him to come back out and check the ductwork and see if it is sized properly.

    He has already done more than what alot of contractors would do.

    By the way, if you want to test and see how good the other contractors might be, do not offer them the info that the original contractor gave you on sizing the new unit. See if they are willing to do their own load calcs based on what you tell them your needs are.

  8. #8
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    Very doubtful you need to increase by 1 ton to drop 3* additional temp.
    When you say drop.
    Are you setting your stat back, and then try to lower temp when its 91* outside.
    Also, can you add insulation to the attic to help reduce the size A/C you need.
    Have you ever considered replacing those windows. To save on heating and cooling cost.
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  9. #9
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    Quote Originally Posted by forcryinoutloud View Post
    Since it looks like he has already done the load calc and came up with 3.2 tons required, I would ask for him to come back out and check the ductwork and see if it is sized properly.

    He has already done more than what alot of contractors would do.

    By the way, if you want to test and see how good the other contractors might be, do not offer them the info that the original contractor gave you on sizing the new unit. See if they are willing to do their own load calcs based on what you tell them your needs are.
    Did he actually do a load or did he go by square feet of floor area?
    Remember, Air Conditioning begins with AIR.

  10. #10
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    Quote Originally Posted by Kevin O'Neill View Post
    Did he actually do a load or did he go by square feet of floor area?
    You mean like 1800/560 sq ft per ton=3.21 tons.

    Thats what I'm wondering.

    I've never had a house that had a problem of losing 2 or 3 degree temp, need to jump 1 ton, unless the old unit was a 4 ton unit.
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