Novice with general new construction questions - Page 2
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  1. #14
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    http://en.wikipedia.org/wiki/Trust,_but_Verify

    I WOULD TRUST THE BUILDER
    just about
    EQUAL TO ... the boston bomber.

    He doesn't happen to be Russian, does he?
    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

  2. #15
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    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

  3. #16
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    My biggest concern is not adequately cooling the house. It sounds like the 9 tons may be a little much but I don't mind paying more for a comfortable home during our long summers. Is there any harm in having a "larger" system (9 ton total vs. 4-6)?
    Those 2 stage units will be operating at anywhere from 2.1 to 2.4 tons capacity in first stage. And probably won't dehumidify very well, so you will end up having to cool the house to a lower temp. Which means paying more yet to be comfortable. Which defeats the purpose of a foamed house(almost like going to a casino to save money).

    If your going to let them put in 9 tons anyway. get a whole house dehumidifier installed right a way also. So you don't have to set your thermostats to 66 to be comfortable.
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  4. #17
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    Sep 2009
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    Arnold mo
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    Here's a quote from a guy living in Texas:

    "I heat & cool at least 4,000 sq. ft. with one 2 ton heat pump in north central Texas."

    You can read more of Paul42's posting here:
    http://hvac-talk.com/vbb/showthread....as-tight/page2

    Of course having 3 separate units in 3 different zones throughout the house is not the same thing as having one huge 9 ton a/c blasting out all at once, but it's still something to consider.
    An answer without a question is meaningless.
    Information without understanding is useless.
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  5. #18
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    If the units are in the attic, then you should foam the roof deck and seal the attic... If you aren't planning to already. That will drop capacity requirement by at least 10%to start.

    No reason 3 2ton units won't be adequate in a foam house that size. Larger homes have less surface area to volume and proportionally more mass too. They do not change temperatures quickly. It might take 3 hours when ion a100k day to cool the house of by 1f, but it will hold temp on single stage.


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  6. #19
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    Quote Originally Posted by motoguy128 View Post
    If the units are in the attic, then you should foam the roof deck and seal the attic... If you aren't planning to already. That will drop capacity requirement by at least 10%to start.
    POST # 6 - I believe "Ducts in conditioned space" reduce load by close to 30% based on ASHRAE Manual J8.
    You are putting the air handler and SIGNIFICANT AMOUNT of duct in an ~ 80'F environment, instead of 140'F in TX.

    IF not putting foam on the roof deck and using 3 units ( Only 2 actually needed ), the required duct work space may necessitate that the duct be stacked about 5 feet high.

    The _extended plenums_ must be arranged so that they fit on specific horizontal planes unless the units are separated by about 30 feet.
    FLEXIBLE DUCT LENGTH MUST BE < 12 FEET or one ends up with the usual 20+% reduction in air flow and capacity.
    Last edited by dan sw fl; 05-04-2013 at 06:47 AM.
    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. #20
    Thanks again for the advice Dan. I've asked my builder about the manual J calculations and duct design as you suggested and should hear back after the weekend. I'm pretty sure he told me at the beginning of construction the HVAC contractor did a load calculation for the house but as you suggested, it's worth verifying. The proposal by the contractor, assuming we're using 3 units, was for all of the units to be in the attic space above the 2nd story. 1 unit would supply the 2nd story (3 bedrooms, 2 bathrooms, hall and large game room),1 unit for 1st story below the 2nd story area (kitchen, breakfast area, laundry,2 halls, mud room, bedroom, and dining room), and 1 unit for rest of house (2 story family room, study, hall, master bedroom and bath). Would the unit supplying the family room, study, hall, and master be better off being centrally above these areas in the attic (above study between family room and bedroom) or is it ok for it to be with the other 2 units above the 2nd story game room? In other words, would it be possible for it to cool our master bedroom adequately if the unit is that far away from it (roughly 50 feet away) if proper duct work was used?

  8. #21
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    Oct 2010
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    Anderson, South Carolina, United States
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    As long as its properly sized (per manual j/d), sealed and insulated it should be ok being 50ft away. There is no way in the world a spray foamed house needs 9 tons. Maybe 4-5 but that's still probably too much. With 9 tons you will definitely need a whole house dehumidifier or 2 to keep humidity levels in check. If you can cut the size of equipment down then the size of the ducting required is smaller so its easier to conceal without cramming it in somewhere or squishing flex into every nook and cranny and restricting flow. Also the return grilles will be smaller and you will have less surface area of duct in the semi-conditioned space (sf attic) so you won't gain/lose as much through the long duct runs. Not to mention it will its less up front, cost less to operate, produce more even temps and remove adequate humidity if its sized correctly

  9. #22
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    Oct 2010
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    Anderson, South Carolina, United States
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    Be leery of a builders hvac sub, they tend to put to large of equipment in (because more profit margin) and be on the builders side rather than the homeowner (keeping it cheap) so they put more $$$ in the builders pocket and get to continue doing their sub work. I would want to hire my own subs because what's a few grand more up front to have it done right on a 15-30 year mortgage, a few dollars a month?

  10. #23
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    Quote Originally Posted by jtrammel View Post
    Be leery of a builders hvac sub, they tend to put to large of equipment in (because more profit margin) and be on the builders side rather than the homeowner (keeping it cheap) so they put more $$$ in the builders pocket and get to continue doing their sub work. I would want to hire my own subs because what's a few grand more up front to have it done right on a 15-30 year mortgage, a few dollars a month?
    With PROPER PLANNING AND an experienced installer, the new construction project would cost a lot less due to use of two 2-ton WITH A LOT LESS DUCT WORK.

    Homeowner can come back here in 3 years to tell the builder/hack/ amateur engineer story
    _ _ _ _ _ _ _ IF I WOULD HAVE ONLY LISTENED ... ... ... ... coulda, woulda, shoulda, ... ... ... ... ...
    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

  11. #24
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    Quote Originally Posted by loganparker View Post
    Thanks again for the advice Dan. I've asked my builder about the manual J calculations and duct design as you suggested and should hear back after the weekend. I'm pretty sure he told me at the beginning of construction the HVAC contractor did a load calculation for the house but as you suggested, it's worth verifying. The proposal by the contractor, assuming we're using 3 units, was for all of the units to be in the attic space above the 2nd story. 1 unit would supply the 2nd story (3 bedrooms, 2 bathrooms, hall and large game room),1 unit for 1st story below the 2nd story area (kitchen, breakfast area, laundry,2 halls, mud room, bedroom, and dining room), and 1 unit for rest of house (2 story family room, study, hall, master bedroom and bath). Would the unit supplying the family room, study, hall, and master be better off being centrally above these areas in the attic (above study between family room and bedroom) or is it ok for it to be with the other 2 units above the 2nd story game room? In other words, would it be possible for it to cool our master bedroom adequately if the unit is that far away from it (roughly 50 feet away) if proper duct work was used?
    ONLY THE ONE WHO DESIGNS THE DUCT REALLY KNOWS
    ( OR is this case he might think he knows, but this is probably his first house).
    I have only done ~ 500.
    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

  12. #25
    It's tough as a consumer to know who to trust. The contractor being used for the HVAC has been in business since 1973, is licensed, and is part of the BBB with no complaints. Not only that but everyone in my area who has a house my size have 3 units as well. Maybe all the HVAC contractors around here are in cahoots. What's a consumer to do? Are the manual j/d reports something a novice such as myself would be able to understand?

  13. #26
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    Quote Originally Posted by loganparker View Post
    1. What's a consumer to do?
    2. Are the manual j/d reports something a novice such as myself would be able to understand?
    You can trust someone who does Not have their hands in Your Deep Pockets.

    1. Stop work until duct layout drawings and equipment specs/ AHRI #s are provided.!

    2. Read Manual J8 attachments to post #6.
    ... Then answer your rhetorical question.

    _________ ((( ))) ____________
    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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