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  1. #1
    Join Date
    Dec 2011
    Location
    bedford ind
    Posts
    1,090

    what size would you do.

    Got a call to install an evap. coil and a/c in a modular. Total square foot about 1300, 2 x 6 walls, minimal windows, new house. The factory installed a 4 ton blower in the a/h with 15 kw. There are a total of 6, count them SIX vents 2 1/4 by 12. Also r32 in attic. No adding new vents. Return is 20" flex.

  2. #2
    Join Date
    Sep 2008
    Location
    VA
    Posts
    1,768
    Do a load calc, and advise whomever, what needs to be done to do the job properly. If they want it done otherwise, just make sure you get it in writing that they were advised.
    Funny how some consumers can be so penny wise!
    "The only true wisdom is in knowing you know nothing" Socrates

  3. #3
    Join Date
    Nov 2010
    Location
    cali
    Posts
    94
    load calc is the best way to go, the only way to ensure how many btu's are required sounds like a 4 ton is a little large to me. depending on heat load calc i would roll with a 3 ton with 10 kw. not sure the area your in but there is a formula to determine HS kw..

  4. #4
    Join Date
    Sep 2008
    Location
    VA
    Posts
    1,768
    What about using a lower rpm motor? Maybe an Evergreen, or something. Then pull one lead off a 5kw strip, and use turning vanes in the supply T.
    If you're worried about the heat, use a two stg stat and set the differential high. Even at 15kw / 800 cfm it will only be about a 60* rise.
    Last edited by mgenius33; 08-13-2012 at 12:09 AM.
    "The only true wisdom is in knowing you know nothing" Socrates

  5. #5
    Join Date
    Dec 2011
    Location
    bedford ind
    Posts
    1,090
    Load cacl isn't going to help my pressures. Fairly mild winters around patoka lake. They are hard from time to time. We commonly use 2 1/2 or 3 ton for this type of home. Only they have more supplies.

    The heat isn't my problem. The a/h came with the home.

    I'm still dealing with a 4 ton blower and 6 supplies going on a 2 1/2 or 3 ton ac.

    I was hired for a/c only.

  6. #6
    Join Date
    Aug 2007
    Location
    Elkhorn, Wisconsin 53121
    Posts
    21

    AC size

    I'd be hesitant as well with out adding supplies and return. The way it stands I'd be at 1.5 tons with 2 ton evaporator and set fan to medium speed then see the pressures. Still not the best setup. I'd prefer a 2 ton with 4 more supplies. I think any larger with the good insulation you state would be too big.


    Quote Originally Posted by ironpit View Post
    Load cacl isn't going to help my pressures. Fairly mild winters around patoka lake. They are hard from time to time. We commonly use 2 1/2 or 3 ton for this type of home. Only they have more supplies.

    The heat isn't my problem. The a/h came with the home.

    I'm still dealing with a 4 ton blower and 6 supplies going on a 2 1/2 or 3 ton ac.

    I was hired for a/c only.

  7. #7
    Join Date
    May 2003
    Location
    Utah
    Posts
    732
    There is no cookie-cutter answer when it comes to selecting equipment. Load calc....that's it.

    Not meaning to sound critical, but......Is it just me, or is there a basic problem when a technician/business owner comes out here to ask fellow posters how to properly select equipment for a job?

    This is certainly a good place to share ideas, experiences, etc. But if you're not capable of selecting/sizing/designing the proper equipment for a job and have to resort to assistance from an online group....might want to consider taking the necessary steps to ready yourself for this task.

  8. #8
    Join Date
    Aug 2012
    Location
    Palmyra, Missouri, United States
    Posts
    224
    Mobile home ductwork is awful.

  9. #9
    Join Date
    Dec 2011
    Location
    bedford ind
    Posts
    1,090
    Thank you for the friendly advice. LOAD calcs DO NOT answer all questions.
    LOAD CALCS are not cookie cutter annswers. You have to see the bigger picture. I don't have time to explain all of the details.

    I think the guys have a handle on the scenario.

    I have six vents for a 4 ton blower with 5 x 15 duct. We are going to have pressure problems as we are not allowed to increase circulation..

    We are going to have a heat transfer problem.

    Last time I checked load calcs had something to do with ductwork.

    But that is just me. 4 tons is way too big to cool this house.

    But I guess, really, I was just frustrated and wanted to share my feelings, with the guys. I really didn't want their advice.

  10. #10
    Join Date
    Aug 2012
    Location
    Palmyra, Missouri, United States
    Posts
    224
    Surely the blower has multi speed selections. Call manufacture and find out what lower speed selections will do for your small duct.

  11. #11
    Join Date
    Dec 2011
    Location
    bedford ind
    Posts
    1,090
    checked them. Thank you. The home owner is not open to new vents in her new floors.
    No vents in three rooms, including the laundry ion the north end.

    The factory should have done this right. This lady doesn't want the belly of her house cut open, to run new duct in a house that was supposed to be done right in the first place. The bathroom, dining room and laundry have no vents.

    This is one of those I can't believe it jobs.

  12. #12
    Join Date
    Dec 2011
    Location
    bedford ind
    Posts
    1,090
    The really annoying thing is this house was sold by my accountant.He sells modulars.

    He originally asked me if I was interested in the duct work and furnace part of the job, but I was swamped so I told him no. Plus the job is about 60 miles away.I told him he would save a lot of money and time to have the factory do it. They would do it right. The factory was unbelievably cheap. I couldn't touch their price.

  13. #13
    Join Date
    Aug 2007
    Location
    Elkhorn, Wisconsin 53121
    Posts
    21
    So, how old is this modular? shouldn't the manufacturer have some obligation to correct this? Warranty? Your Accountant has the pull to get this done as the selling dealer. I know the present owner doesn't want the floors cut for additional vents but they could be swayed to see the long term benefits? Is it on a crawl space? It could be done and insulation sealed back up properly but, labor intensive which is why the manufacturer should bare some financial responsibility.

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