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  1. #1

    New Construction HVAC - Am I being oversized??

    Good morning,
    I am building a new house in the piney woods of east TX. H/C area of the house is 2800. All windows face east and west but most are under covered porches. The sun doesnt really hit the windows due to so many trees around. Spray foaming walls and roof deck with open cell foam. Had the HVAC contractor come out, (very reputable, highly recommended,never heard any complaints, excellent service company, does many foam houses) come out. This is what they recommended from looking. They had not ran a Manual J yet and are going to. They said 1 - 4 ton Carrier Infinity variable speed Heat pump to service most of the house, and 1 - 2 ton to service the master suite, utility, mudroom. The spray foam guys came and said that is way over sized and they ran a manual J that said I need 3.4 tons total. When I told the HVAC guys, they said that is true, and that I will need approximatly 3 tons total to cool the house. They said the reason they went with a 4 ton and 2 ton variable speed was 90% of the time I will be running both units @ 50% essentially 3 tons. In the case we have a bunch of people over or it reaches the 110* days it usually does in June, July August in TX, that it then has the capacity to take care of that. HVAC guys said their # 1 concern is humidity control and comfort. Does setup they recommend seem appropriate?
    Thanks

  2. #2
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
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    5,060
    Quote Originally Posted by cdlgolf View Post
    Good morning,
    I am building a new house in the piney woods of east TX. H/C area of the house is 2800. All windows face east and west but most are under covered porches. The sun doesnt really hit the windows due to so many trees around. Spray foaming walls and roof deck with open cell foam. Had the HVAC contractor come out, (very reputable, highly recommended,never heard any complaints, excellent service company, does many foam houses) come out. This is what they recommended from looking. They had not ran a Manual J yet and are going to. They said 1 - 4 ton Carrier Infinity variable speed Heat pump to service most of the house, and 1 - 2 ton to service the master suite, utility, mudroom. The spray foam guys came and said that is way over sized and they ran a manual J that said I need 3.4 tons total. When I told the HVAC guys, they said that is true, and that I will need approximatly 3 tons total to cool the house. They said the reason they went with a 4 ton and 2 ton variable speed was 90% of the time I will be running both units @ 50% essentially 3 tons. In the case we have a bunch of people over or it reaches the 110* days it usually does in June, July August in TX, that it then has the capacity to take care of that. HVAC guys said their # 1 concern is humidity control and comfort. Does setup they recommend seem appropriate?
    Thanks
    It would appear that your insulating company is fare more competent than your
    (very reputable, highly recommended,never heard any complaints, excellent service company, does many foam houses) is.

  3. #3
    What would any of yall recommend with the few details I have provided? Any sizing, setup recommendations?

  4. #4
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    With variable capacity, or multistage equipment, it is ok to go over 1/2 a ton, maybe 1 ton on a house of that size, but 3 tons? NOOOOO

    One of my happiest customers is one who let me put a 2 ton 2 stage heat pump in his 2000 square foot foamed house, against the advice of his builder, and the builders regular HVAC guy, who both wanted to put a 3.5 ton system in.
    If more government is the answer, then it's a really stupid question.

  5. #5
    Join Date
    Jan 2009
    Location
    Keokuk, IA
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    5,520
    Quote Originally Posted by second opinion View Post
    It would appear that your insulating company is fare more competent than your
    (very reputable, highly recommended,never heard any complaints, excellent service company, does many foam houses) is.

    +1.

    I'd put in a 3 or 4 ton Carrier Greenspeed along with a whole house dehumidifier to handle more of you latent load (dehumidification) and an ERV for ventilation.


    IF it was my house, I'd put in a air cooled or geothermal water to water unit and install a properly sized fan coil for each room and do a 2 pipe system chilled and hot water system. IF you have a big exhaust hood in the kitchen, I'd also add a make-up air unit.

    With foamed homes, humidity control and ventilation become you biggest issues.

    I think 3.4 tons is pretty conservative with the shading you have. I suspect 2 tons will carry the house over 90% of the time and the other times the house will heat up and cool off slow enough that it won;t be an issue.


    Make sure and concrete slabs and foundation you have are insulated from the exterior. You want all the thermal mass you can get to help reduce peak heating and cooling loads. Brick, stone, tile floors, hardwood floors, plaster and real stucco on the exterior are great too. I think all homes in hot climates should have light colored stucco to tighten up the home and reduce peak cooling loads. If you can, add a cool roof design as well. Metal roof panels on furring strips with a radiant barrier and 1/2" foam board under that.

    Don't fear... I have 4 tons combined cooling 3200sqft home and only have a foamed roof deck, but not nearly the wall insulation you home will have, but a lot more windows (30% window area, few modern homes are that high... he house was built in 1925). I held 76F indoors upstairs in 103F last July. It can be done.

  6. #6
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,164
    what they are doing is a combination of cya
    & upselling equipment.

    you wrote:
    "The spray foam guys came and said that is way over sized and they ran a manual J that said I need 3.4 tons total. When I told the HVAC guys, they said that is true, and that I will need approximatly 3 tons total to cool the house. They said the reason they went with a 4 ton and 2 ton variable speed was 90% of the time I will be running both units @ 50% essentially 3 tons. In the case we have a bunch of people over or it reaches the 110* days it usually does in June, July August in TX, that it then has the capacity to take care of that. HVAC guys said their # 1 concern is humidity control and comfort. Does setup they recommend seem appropriate? "

    so in low speed...you get 3 tons. but look at what you will pay
    for the two units @ 50% capacity 90% of the time.
    it is a old time sales tatic that whole people over when its 100 degrees..
    and its bs.
    they probably told you that when one unit goes out...
    you still have a place to go where its cool.
    poor justification for not understanding how to correctly size
    & install equipment.

    their way they make xxx times more money. that you pay
    to purchase, maintain & operate.

    who does the foam co recommend? if they have worked sucessfully
    with another hvac company...one that gets it...get the name & call them.

    this is a common scenerio when we build better & hvac company comes
    in & screws it all up with oversized equipment.

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

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,913
    6 tons of 2 stage equipment won't control humidity in a 4 ton load house. You'll need a whole house dehumidifier.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  8. #8
    Join Date
    Jun 2007
    Location
    Round Rock
    Posts
    3,549
    6 is too much, but 3.5 may be a little on the shy side when it gets really hot out. You're foaming roof deck, so you have the uninsulated and unconditioned attic space to take into account. The insulation guys are usually a little low to promote their product. And the a/c guy doesn't want a call in August with you *****ing the house won't get below 80 when it's 105 out. What the number is, I have no idea. But somewhere in between there.
    I like DIY'ers. They pay better to fix.

  9. #9
    Join Date
    Nov 2004
    Location
    SW FL
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    6,273
    Quote Originally Posted by cdlgolf View Post
    What would any of yall recommend with the few details I have provided?
    Any sizing, setup recommendations?
    I Don't know,
    do you have 645 Sq feet of single pane glass U-value 1.1
    or
    do you have 200 sq feet of U-value 0.26 with SHGC 0.29 ?

    ACH = 0.5, 1 or 2?

    Wall R-5 or R- 21?
    Ceiling R-34

    Thermostat set to 71 or 81?

    3 tons < Recommendation < 7 tons

    RECOMMENDATION ,,, TIE DOWN SOME of The Details.
    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

  10. #10
    Join Date
    Aug 2006
    Location
    Pennsylvania / NJ
    Posts
    155
    Two stage air conditioners run at 67% of their total capacity when in low stage........not 50%. Get a second, professional opinion.

  11. #11
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
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    14,914
    Quote Originally Posted by ComfortAdvisor View Post
    Two stage air conditioners run at 67% of their total capacity when in low stage........not 50%. Get a second, professional opinion.
    To make it worse, most of the units with 2 step scroll compressors actually run in the 70-80% total system capacity range in 1st stage.
    Trane XL20i and American Standard Platinum ZM systems run at 50-60% capacity in first stage, but they have 2 compressors.
    If more government is the answer, then it's a really stupid question.

  12. #12
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,273
    Quote Originally Posted by cdlgolf View Post
    Good morning,
    I am building a new house in the piney woods of east TX. H/C area of the house is 2800. All windows face east and west but most are under covered porches. The sun doesnt really hit the windows due to so many trees around. Spray foaming walls and roof deck with open cell foam. Had the HVAC contractor come out, (very reputable, highly recommended,never heard any complaints, excellent service company, does many foam houses) come out. This is what they recommended from looking. They had not ran a Manual J yet and are going to.

    When I told the HVAC guys, they said that is true, and that I will need approximately 3 tons total to cool the house.


    Does setup they recommend seem appropriate?
    The Texas construction permitting set-up definitely seems quite weird.

    HOW does one obtain a Construction PERMIT withOUT a HEATING & COOLING LOAD ANALYSIS?

    I guess Texas must be far behind many other states in their Residential Building code.!

    ICC version which most codes now follow regarding Energy Efficiency would be ...

    " M1401.3 Sizing. Heating and cooling equipment shall be sized in accordance with ACCA Manual S based on building loads calculated in accordance with ACCA Manual J or other approved heating and cooling calculation methodologies. "

    ... other methodologies .. = ASHRAE Fundamentals
    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
    May 2004
    Location
    south louisiana
    Posts
    3,164
    windows get no direct sun due to porches.

    you could put one 4 ton system & zone it (multiple tstats...not units)
    for less than the cost of what they propose.

    2 tons on master bedroom is overkill unless this area is 1400 sq ft or larger.

    one thing you will want is a pathway for return air from mbs. usually
    master bedroom has 2 supplies, each closet has 1 supply & bathroom
    has 1 supply. either a seperate return in this area, or a jump duct
    or transfer grill to return all the air supplied.
    undercutting the door only allows return for 1 supply.
    the details are what will make your comfort.

    has foam company worked with a hvac company sucessfully in
    their past projects. this would be the best option.
    else you'll have the same discussions with multiple companies...
    selling more equipment.
    usually the homeowner after getting the same bs runaround gives
    in to multiple units set to lower speed...at a huge cost as opposed
    to one unit correctly sized designed & installed.
    been there...done that.

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

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