Results 1 to 8 of 8
  1. #1
    Join Date
    Jun 2005
    Posts
    3

    Question

    I will be replacing a carrier 2.5 packaged heat pump with a rudd 3.5 ton packaged heat pump due to an addition to our house of 420 extra square feet. I have decided to switch brands due to the poor performace and troubles I have had with the carrier - recent problem - leak on inner coil which is rather expensive to have replaced. Unit is only 6 years old. An additional return will be added to the new addition - currently only have one return. I have two (2) questions. The model number of the rudd I am getting is RQMJ-A042JK010 12seer 3.5 ton packaged heat pump. Does this seem to be a good unit if properly installed. 2nd question. They will be installing a y to the existing flex duct on the existing return and running to the new return. The current return has 14 inch flex duct running to the unit. Is this large enough or does this need to be increased in size. I have had someone tell me this is not large enough and could possible 'starve' the unit for air?? The current trunk line is 14inch. They will be increasing this to 16 inches for the first 12 feet comming off the unit. All comments / help will be greatly appreciated.

  2. #2
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,766
    14" flex return is small for 3.5 ton.

    When you ask them about it, they'll tell you that the return doesn't have as much restriction as the supply because it is sucking the air back, BS!

    You can't supply anymore air then you bring back.

    Have them do a manual D.

    Sounds like they just guessed what size you need also.

    Should have done a manual J.
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  3. #3
    Join Date
    Jun 2005
    Posts
    3
    Thank you for the response. What is a manual J and D? I assume I should go to at least a 16 inch on the return.

  4. #4
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,594
    For proper airflow, 20" flex at minimum for 1400 CFM according to my ductulator. I use 14" flex on my 2 ton system.

  5. #5
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Many package units have higher ESP(static0 capabilities than split systems.On mobile/manufactured homes a 16" "could" be possible,often it's better to run two 14's ,due to space allowed.


    We need the fan data chart for the equipment being used,Man D would get the ducts sized right.

    An extra ton for a 420 sq. ft addition sounds high,Man. J would get the right size.

  6. #6
    Join Date
    Nov 2002
    Location
    VA
    Posts
    296

    Manual J and Manual D

    hawk0626;

    The two mentioned methodologies are industry standard best practices for calculating residential Heating and Cooling Loads (Manual J) and designing air distribution systems (Manual D) for residential systems. They have been published by ACCA who complied much of the data from other authoritative sources. Most notably the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) for Manual J and the Sheet Metal and Air Conditioning Contractors National Association (SMACNA) for Manual D.

    Both of these "Manuals" are available free of charge through your local inter-library loan program. If you have a reasonable command of high school level algebra neither present a challenge to comprehend. That said please allow me to caution you not to attempt to study ACCA's Manual J Eight addition, it is fraught with serious problems and is in the process of a major revision. Instead please insist that your Library obtain a copy of the Seventh Edition for you which has indeed embraced as an industry standard for the past several decades. The computer application offered for sale at the top of this page is based upon ACCA's Seventh Edition of Manual J (with relevant additions to cover newer material types).

    The other gentlemen who have answered your query are tenured wise veterans of the industry and as such they have given you excellent guidance, enough said.

  7. #7
    Join Date
    Jun 2005
    Posts
    3

    Dash - Thank you for the advice. Extra ton does seem much for 420 sq. ft but current system was not performing well prior to the addition. I am now heating/cooling 2250 sq. ft. Front of house faces east in the morning and west in the evening. I have 8 windows in front and 6 in the back all which measure 30 by 72 with no tinting. I have 8 foot ceilings - new addition has 12 foot vaulted ceiling. Insulation levels - R 33 ceiling, R 13 outer walls, R 19 crawl space. I live in SC and the summers get rather hot. Not sure if this is the info on the fan data chart you are refering to. I pulled it off the spec sheet - Diameter - 1/24 / drive type - direct / cfm - 4200. Any thoughts. Thank you.

  8. #8
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Originally posted by hawk0626

    Dash - Thank you for the advice. Extra ton does seem much for 420 sq. ft but current system was not performing well prior to the addition. I am now heating/cooling 2250 sq. ft. Front of house faces east in the morning and west in the evening. I have 8 windows in front and 6 in the back all which measure 30 by 72 with no tinting. I have 8 foot ceilings - new addition has 12 foot vaulted ceiling. Insulation levels - R 33 ceiling, R 13 outer walls, R 19 crawl space. I live in SC and the summers get rather hot. Not sure if this is the info on the fan data chart you are refering to. I pulled it off the spec sheet - Diameter - 1/24 / drive type - direct / cfm - 4200. Any thoughts. Thank you.

    Maybe a member here will post the fan data,baldloonie often does.

    Remember at least one wall of the original home is now an interor wall,addition has very good insulation,so aMan. j calculation ,would be in order to get the correct size system.


    Getting supply air to the addition can also create problems if the ducts are not properly designed.Man. D,from ACCA can solve that as well.

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