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Thread: Ductwork

  1. #1
    Join Date
    Sep 2012
    Posts
    18

    Ductwork

    In advance thanks for all replies, you knowledge and expertise is greatly appreciated.

    I have had 3 different contractors look at my home to update the heating and cooling.

    1-100,000 BTU/4 ton HP
    1-70,000 BTU/3 Ton HP
    1-60,000 BTU/2 Ton HP

    Non of them performed a Manaul J, but I did have one performed on my own.

    The 60,000 BTU/2 Ton HP came up the closest to the Manual J (1600 sqft 44,000 Heat Loss/14,000 Heat Gain)

    The two that oversized stated they did so due to the amount of ductwork, the one that was closest stated it would work fine.

    Your Opionions.

  2. #2
    Join Date
    Jun 2007
    Location
    Greenwood Indiana (Indianapolis)
    Posts
    420
    Heat load and gain has a lot to do with the location you are at. IMO, it sounds like the 14,000 btu. gain is way low. There again, I don't know your location. Here in central Indiana, your home would most likely call for a 2.5 ton- 2 ton. It is a rule of thumb to upsize a heat pump a half a ton so you get more heat in the winter time. Here is a thought, get a 2 speed 3 ton hp, it will run at 2 tons mostly but if you ever need more power, than it boosts itself to 3 ton.

    Good luck
    As iron sharpens iron so one man sharpens another Proverbs 27:17 NIV84

  3. #3
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,012
    Quote Originally Posted by remodel80 View Post
    I have had 3 different contractors look at my home to update the heating and cooling.

    1-100,000 BTU/4 ton HP
    1-70,000 BTU/3 Ton HP
    1-60,000 BTU/2 Ton HP

    Non of them performed a Manual J, but I did have one performed on my own.

    The 60,000 BTU/2 Ton HP came up the closest to the Manual J (1600 sqft 44,000 Heat Loss/14,000 Heat Gain)

    The two that oversized stated they did so due to the amount of ductwork, the one that was closest stated it would work fine.
    Your Opinions.
    Does that 14,000 Heat Gain include the latent heatload Btuh?
    If it does, then we're talking about a 1.5-Ton heat pump for the cooling load.

    Two of them appear to be way oversizing the equipment; 4-Ton cooling wow.

    The duct system will usually work okay, & perhaps more efficiently, because it's usually under-sized for 4-Ton of cooling & 100,000-Btuh for heating.

  4. #4
    Join Date
    Sep 2009
    Location
    Arnold mo
    Posts
    3,971
    2 speed is the way to go, even for straight a/c. I'm no heat pump sizing pro, but I believe climate zone plays a part, but a heat pump is usually unable to to be sized to meet your heating needs because it results in an oversized air conditioner in summer. Assuming your ducts are sized correctly, a 2 speed makes good sense, considering all properly sized a/c's are oversized for the majority of the cooling season because single speeds have to be sized to meet the peek load conditions of summer, which is a small percentage of time. A 2 speed heat pump will allow you to meet more of your heating load by running in 2nd stage, and in summer it will likely stay in 1st stage the majority of the cooling season, with 2nd stage as a back-up for a heat wave.
    An answer without a question is meaningless.
    Information without understanding is useless.
    You can lead a horse to water............
    http://www.mohomeenergyaudits.com

  5. #5
    Join Date
    Sep 2012
    Posts
    18
    My main trunk line is 18"x16" for 12' the turns and reduces to 13"x17" for 37', there are 4-6 round and 7-8 round runs off of this.

    And all quotes where for 2 stage heatpumps since I knew that they most likely would be oversized for the cooling side.

    Also I am in central Illinois

  6. #6
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,328
    Quote Originally Posted by remodel80 View Post
    My main trunk line is 18"x16" for 12' the turns and reduces to 13"x17" for 37', there are 4-6 round and 7-8 round runs off of this.

    And all quotes where for 2 stage heatpumps since I knew that they most likely would be oversized for the cooling side.

    Also I am in central Illinois
    Should we guess that it's a 1953 ranch?
    and that it's 1,600 square feet without a basement?
    and it only has 7.5 windows?

    Double Jeopardy game doesn't always work that well here.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  7. #7
    Join Date
    Sep 2012
    Posts
    18
    Dan,
    It is a 100 year old two story with a addition done last year.
    Basically 1600 sqft on the first floor, second story is heated and cooled by seperate system,9' 800 sqft basement, 400 sqft cellar type basement, remainder crawl space. There is 14 windows 10 of them 6'x30" the rest 4'x30", 1-6' Slider and 2-36" Entry doors.

    I have completely remodeled the 100 year old (Everything new but the wood in the walls) and added approx 1,000 sqft to the first floor last yeat which is when the basment was installed. The duct work I listed was installed with the new addition, and I continued to use my existing system which is a 90% 100,000 BTU Furnace.

  8. #8
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,328
    Quote Originally Posted by remodel80 View Post
    Dan,
    It is a 100 year old two story with a addition done last year.
    Basically 1600 sqft on the first floor, second story is heated and cooled by seperate system,9' 800 sqft basement, 400 sqft cellar type basement, remainder crawl space.
    There is 14 windows 10 of them 6'x30" the rest 4'x30", 1-6' Slider and 2-36" Entry doors.

    I have completely remodeled the 100 year old (Everything new but the wood in the walls) and
    added approx 1,000 sqft to the first floor last year
    which is when the basment was installed.
    The duct work I listed was installed with the new addition,
    and I continued to use my existing system which is a 90% 100,000 BTU Furnace.
    30,220 BTU/HR Heating
    20,710 BTU/Hr Cooling for 1,600 Sq. Ft. FIRST Floor

    Windows 240 sq feet at U value of 0.3 with 120 Square Feet facing E/W
    Walls R15
    Average Infiltration yields 7,400 BTU/HR
    Manual J abridged 8th edition

    Seems a bit low on heating but the differential temperature is 75'F ( 72' - -3')

    1000 sq feet ceiling R30 because second story covers about 600 square feet

    I'm going to have to reconfirm calc
    because 30,200 BTU/HR
    just doesn't "feel right/ accurate", but
    It Is, What It Is.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  9. #9
    Join Date
    Sep 2012
    Posts
    18
    S Wall 36'/Windows 48sqft/R15
    N Wall 36'/Windows 66sqft/R22
    E Wall 44'/Windows 30sqft/28' R22/16' R15
    W Wall 44'/Windows 65sqft/28' R22/16' R15

    Window Values
    U Value-0.28
    SHGC-.18
    R Value 3.57
    Attic-R60
    Ceiling of 1st floor over 2nd Floor R-30

    I was in unbelief when I had the load calc performed.

    My current AC is 2ton, 27 years old. I made it through this summer comfortable and it actually was leaking refrigerant.

    The load calc also included my basement if that makes a difference.

  10. #10
    Join Date
    Sep 2012
    Posts
    18
    My bad my walls are 9'

  11. #11
    Join Date
    Sep 2012
    Posts
    18
    Load Calc Was based on the following information as well, I should probably just load up a copy but dont know if that is allowed.

    Indoor
    Summer Temp 72
    Winter Temp 73
    RH-50

    Outdoor
    Summer Temp 93
    Winter Temp 0
    Summer grains of moisture 194
    Daily Temperature Range Medium

  12. #12
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,328
    Quote Originally Posted by remodel80 View Post
    S Wall 36'/Windows 48sqft/R15
    N Wall 36'/Windows 66sqft/R22
    E Wall 44'/Windows 30sqft/28' R22/16' R15
    W Wall 44'/Windows 65sqft/28' R22/16' R15

    Window Values
    U Value-0.28
    SHGC-.18
    R Value 3.57
    Attic-R60
    Ceiling of 1st floor over 2nd Floor R-30

    I was in unbelief when I had the load calc performed.

    My current AC is 2ton, 27 years old. I made it through this summer comfortable and it actually was leaking refrigerant.

    The load calc also included my basement if that makes a difference.
    IF your SHGC is actually 0.18, I'd suspect that you _NOT_ may be able to see through them so-to-speak.
    ( in other words, darker than h_LL).

    Please verify that value with a purchase order, window tag, vendor catalog or correspondence with the window mfg representative.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  13. #13
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,328
    Those windows have got to be something REALLY SPECIAL.

    http://www.efficientwindows.org/glazing_.cfm?id=8
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

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