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  1. #1

    Hmm Single stage vs two stage system

    Building new house. 4500 sq ft. Each side of house will be controlled by separate HVAC systems. Contractor has recommended Coleman 5 ton 18 SEER split system with 110,000 BTU (Model AC8B048FC34T18S condenser; Model FC62D3XN15T coil; Model TM8X100C20MP11 furnace) for one side of house and Coleman 4 ton 18 SEER split system with 90,000 BTUs (Model AC8B036FC34T18S condenser; Model FC483XN15T coil; Model TX8X100C20MP11). I favor upgrading to a two stage system 9T, 9V or 9M-12. I also wonder about upgrading to CP9C at 97.5% efficiency. We live in southern New Mexico so the winter can be cold but typically isn't very long so the higher efficiency heating won't likely be recouped in energy savings in any reasonable period of time but the better air conditioning should. Also the better systems have quieter fans and better components (or so I've read) and the quiet is very important. Any advice would be appreciated. Also the estimate for the whole job is running in the$$ range --without the complete details, I know it is impossible for you to be precise on an estimate -- does this seem like it is in the "reasonable" ballpark?
    Last edited by beenthere; 09-03-2012 at 06:23 PM. Reason: price

  2. #2
    Join Date
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    Moore, Oklahoma, United States
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    Welcome to HVAC-Talk. A load calculation will need to be done to determine correct sizing. Since the house is new construction consider spending more on insulating/sealing and less on the HVAC system. 200,000 BTU for heat sounds WAY to big if the house is built right. 9 tons for A/C is conventional construction using the same 500sq ft per ton that hasn't changed since the 60's. Modern insulating practices such as spray foam or Styrofoam can reduce heat gain loss to HALF than of conventional construction. Simply moving ducts into conditioned space reduces heating and cooling loads 25%.

    Unless gas or electricity is really expensive in your area 80% furnaces and 14 SEER A/C units generally have the most reasonable payback time. Also know that SEER is efficiency at 82 degree outside temperature, EER which is sometimes published is rated @ 95 outside temperature. We don't discuss prices on the website (it's against the rules), bids will vary depending on the job.

  3. #3
    Join Date
    Oct 2010
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    Anderson, South Carolina, United States
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    I would look into variable drive mini splits if I were building a new house. Make sure the house is built well, sealed, and insulated. Mitsubishi city multi or daikan, Samsung, and LG are all good mini split manufacturers. These types of units are unmatched when it comes to efficiency. Also they are EXTREMELY QUIET, both indoor and outdoor units. The dehumidify very well too

  4. #4
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    If building a house as large and I assume nice aesthetically I would not skimp on sizing and duct design you will regret it when you are uncomfortable in your house for the next 20 years

  5. #5
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    Quote Originally Posted by jtrammel View Post
    I would look into variable drive mini splits if I were building a new house. Make sure the house is built well, sealed, and insulated. Mitsubishi city multi or daikan, Samsung, and LG are all good mini split manufacturers. These types of units are unmatched when it comes to efficiency. Also they are EXTREMELY QUIET, both indoor and outdoor units. The dehumidify very well too
    Mini splits are sweet no doubt. Buy how do you deal with small rooms like bathrooms/laundry/study/etc. You would need a lot of units to get air in all rooms.

  6. #6
    Join Date
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    Quote Originally Posted by 54regcab View Post
    Mini splits are sweet no doubt. Buy how do you deal with small rooms like bathrooms/laundry/study/etc. You would need a lot of units to get air in all rooms.
    A small ducted air handler

  7. #7
    Join Date
    Jan 2004
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    Lancaster PA
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    The first condenser you listed is a 4 ton, the second one is a 3 ton.


    Pricing questions are not allowed.
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    How many times must one fix something before it is fixed?

  8. #8
    Join Date
    Jul 2006
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    Virginia
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    You will never need that much heat although you might need that size of furnace to get that high of seer rating some times its better to loose a point of seer rating for a correctly sized furnace imop
    We really need change now

  9. #9
    Join Date
    May 2004
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    south louisiana
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    another vote for load calculation.
    investing in air sealing, duct sealing and insulation
    will allow smaller units that will perform better.

    oversized units will cycle on and off, cost you more
    upfront and cost you every month in operating costs.

    as a friend of mine who works for utility company says..
    oversized hvac systems, the gift to utilitie provider that keeps on giving.

    you have the time now to get it right. never agan will you have
    the access & good timing to make corrections.

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  10. #10
    Load calculation was done originally (although I had to demand it) but as I am sure you all are aware, it is not a simple document to interpret. In addition, I am not sure how to determine if the assumptions are reasonable. This is how the tonnage was determined, I believe. The house is well insulated with blown in foam, triple pane low E windows and all duct work is within conditioned space. If quietness is a high priority, then is a two stage system with purportedly better fans, a better choice over the single stage? Any comments on Coleman specifically or is it true that the most important issue is whether the installer knows his equipment? Thanks for the feedback.

    (As a first time visitor, please pardon my question regarding price.)

  11. #11
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    2 stage equipment is usually quieter then single stage. Nothing wrong with Coleman.
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  12. #12
    Join Date
    Nov 2004
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    SW FL
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    Quote Originally Posted by inquiringlizzy View Post
    Building new house. 4500 sq ft. Each side of house will be controlled by separate HVAC systems.

    Contractor has recommended Coleman 5 ton 18 SEER split system with 110,000 BTU (Model AC8B048FC34T18S condenser; Model FC62D3XN15T coil; Model TM8X100C20MP11 furnace) for one side of house and Coleman 4 ton 18 SEER split system with 90,000 BTUs (Model AC8B036FC34T18S condenser; Model FC483XN15T coil; Model TX8X100C20MP11). I favor upgrading to a two stage system 9T, 9V or 9M-12. I also wonder about upgrading to CP9C at 97.5% efficiency.

    We live in southern New Mexico so the winter can be cold but typically isn't very long so the higher efficiency heating won't likely be recouped in energy savings in any reasonable period of time but the better air conditioning should.

    Any advice would be appreciated.
    START WITH THE BASICS ..

    My initial target would be two 3-ton heat pumps / dual fuel units.
    Depending on the floor plan and envelope ( insulation, infilTration, windows/ orientation), I might look at 3 smaller systems.

    What is the annual rainfall? ( humidity)
    What is the elevation?

    I would change the envelope until the house matched my equipment.

    3,000 HDD
    2,400 CDD

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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

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