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  1. #1
    Join Date
    May 2013
    Posts
    6

    Help with my new home HVAC sizing

    We are building a 2900sqft home and I have been getting bids for my HVAC. My problem is that we are getting different opinions on the unit tonnage needed. We are using foam in walls, with zip board system and blown in cellulose in the ceiling and radiant barrier. We live in Tulsa, OK. Our house faces northwest with 4 windows in that direction-1 is under porch. The rear of house is southwestare and all the windows (12) are all under a lg covered porch. 2 window face northeast, and 2 sml are south facing. We requested 2 units because we like to sleep cold with good air movement and thought a sml unit for our side approx 900sqft and a larger one for the reaming 2000sqft. We also have considered just 1 unit and getting a mini-split for our bedroom. We have mostly all 9ft ceilings, but have 10ft in center in living room and kitchen. I would appreciate any suggestions because I don't know who to believe. I also want an ERV air exchanger. Thx for any advice!

  2. #2
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    5,658
    An ACCA manual j or equivalent computer program (ie wrightsoft) is the only way to get the proper heat gain/loss calculation of a house. Anything else is a guess. As for erv, I would reccomend a whole house dehumidifier with outdoor air instead. In a new tight house you should be able to easily get 800-1000 sqft per ton or better. I would also require a blower door and duct blaster test be performed at completion to certify the tightness of the structure and duct system.

  3. #3
    Join Date
    Jul 2001
    Location
    Anderson,SC
    Posts
    950
    jtrammel is correct!
    I'd add a manual d and s.
    I go with a mini-spit for bedroom.
    Don't let the builder drive the train, its your house and you have one chance to get it right. Builders will put a 5 cent HVAC system on a $500,000 house.

    STUD

  4. #4
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    5,987
    Quote Originally Posted by Cwatts15 View Post

    We are building a 2900 sq ft home and I have been getting bids for my HVAC.
    My problem is that we are getting different opinions on the unit tonnage needed.
    We are using foam in walls, with zip board system and blown in cellulose in the ceiling and radiant barrier.
    We live in Tulsa, OK.

    Our house faces northwest with 4 windows in that direction-1 is under porch.
    The rear of house is southwestare and all the windows (12) are all under a lg covered porch. 2 window face northeast, and 2 sml are south facing.

    We requested 2 units because we like to sleep cold with good air movement and thought a sml unit for our side approx 900 sqft
    and a larger one for the remaining 2000 sqft.

    We also have considered just 1 unit and getting a mini-split for our bedroom.
    We have mostly all 9ft ceilings, but have 10ft in center in living room and kitchen.
    I would appreciate any suggestions because I don't know who to believe.
    I also want an ERV air exchanger. Thx for any advice!
    You will have as many opinions + 2 as the number of people you ask.

    Ceiling R- ___ ?
    Walls R- ___?
    Infiltration __ < 0.3 ACH ?

    Design should include mechanical room so equipment and ducts are in conditioned space.

    Window U-value < 0.4, SHGC < 0.35, VT > 0.60

    See Marvin Windows or other.

    http://www.climate-zone.com/climate/...klahoma/tulsa/

    Dual Fuel = Heat Pump + Natural Gas Furnace
    http://www.eia.gov/forecasts/steo/ta...ableNumber=16#

    http://www.eia.gov/naturalgas/

    Electric rate = $0._ _ / kw
    Natural Gas is likely in the range of $0.90 / therm
    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

  5. #5
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    5,987
    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

  6. #6
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,384
    Too many oversize a tight, foamed house. I agree on the bedroom mini. Probably only need a ton or so. Then whatever the 2000 sq ft needs, maybe a 2.5 ton.

    www.energywisestructures.com

  7. #7
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    5,987
    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

  8. #8
    Join Date
    May 2013
    Posts
    6
    Thx for so many replies. We currently live on site where we are building. We built a metal shop and made a sml apartment in it to live till home built. We spray foamed the walls and blew the ceilings in. The one thing I have noticed is the stale air over this last winter. Headaches, sinus problems and cough. I just thought it was the season until we spent time away and no h/a's. Come back h/a, stuffy nose etc. I did not know about the air exchange needed for spray foam insulation. I have read more about it and understand kind of what I need, but some of the HVAC I talked to for bids don't even mention anything about fresh air, just like the guy that installed the HVAC for our apartment. 3 bids- all very different, 1: 2ton & 3ton 80% 13seer Lennox- gas unit with optional ERV, 2: 2ton & 5ton 93% 13seer Armstrong with option fresh air damper. 3: 5ton & mini-split Armstrong. I don't have a program to calculate what I need.
    Now do we need that much tonnage? We are doing all energy star windows too, and open cell foam in walls (2x4)

  9. #9
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    5,658
    All look oversized to me. Is the builder bringing in the subs or are you suppose to be choosing your hvac sub. I would find a good contractor who will do the proper calculations and go over all your options with you.

  10. #10
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,456
    It appears U have a well insulated home with too little air infiltration; you'll need a ventilation system.

    I can't imagine anyone thinking U need 7-Tons of cooling; Tulsa is similar to OKC; maybe a little more humidity but OKC is has low humidity.
    The load-calc below will show you the 'difference' in grains of moisture between outdoors & the indoors room temp-design you select. (I'd never go below 75F; on real hot days U should be comfortable at 76 to 78F & 50% or less humidity.)

    Since U should know the input value numbers; here is an on-line Whole House load-calc for both cooling & heating.
    You have to print the results because U can't save the results.

    I would use .4 Air Changes per Hour (ACH), put the CFM it calculates on the line above, where it estimates the added air you need.

    Print the instructions & steady & follow them; play with it until you are sure you're doing everything right.

    Tell us what load-calcs you get; I think you'll be very surprised!
    Whole House Load-Calc

  11. #11
    Join Date
    Jun 2007
    Location
    Minneapolis, MN
    Posts
    705
    Quote Originally Posted by jtrammel View Post
    An ACCA manual j or equivalent computer program (ie wrightsoft) is the only way to get the proper heat gain/loss calculation of a house. Anything else is a guess. As for erv, I would reccomend a whole house dehumidifier with outdoor air instead. In a new tight house you should be able to easily get 800-1000 sqft per ton or better. I would also require a blower door and duct blaster test be performed at completion to certify the tightness of the structure and duct system.
    This is exactly right and the place in which every properly designed HVAC system starts. Without an ACCA Manual 'J' you simply don't know what you are doing, and neither does you contractor. Most homeowners/builders should hire licensed trades directly, showing them a set of plans and asking them for a sample heat load or Manual 'D' drawing. The heating contractors that can produce a Manual 'J' will be few and far between.

    We specialize in radiant heating systems using Wrightsoft but have been using other modules 'D', 'N' and High Velocity to cover our subs who would rather guess than do the math.

    It doesn't matter where the designer is, as Manual 'J' using your local climate to come to the right loads. Once you have the loads you can spec the heating and cooling equipment, ventilation and duct sizing.

  12. #12
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    5,987
    Quote Originally Posted by Cwatts15 View Post
    Thx for so many replies. We currently live on site where we are building.

    1 .I don't have a program to calculate what I need.
    2. Now do we need that much tonnage?

    We are doing all energy star windows too, and open cell foam in walls (2x4)
    1. No detailed response to post # 4 so a Meaningful Manual J8 cannot be provided.
    2. MIGHT Be ~ 3 tons TOTAL
    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
    5,987
    Quote Originally Posted by udarrell View Post
    It appears U have a well insulated home with too little air infiltration; you'll need a ventilation system.

    I can't imagine anyone thinking U need 7-Tons of cooling; Tulsa is similar to OKC; maybe a little more humidity but OKC is has low humidity.
    The load-calc below will show you the 'difference' in grains of moisture between outdoors & the indoors room temp-design you select. (I'd never go below 75F; on real hot days U should be comfortable at 76 to 78F & 50% or less humidity.)

    Since U should know the input value numbers; here is an on-line Whole House load-calc for both cooling & heating.
    You have to print the results because U can't save the results.

    I would use .4 Air Changes per Hour (ACH), put the CFM it calculates on the line above, where it estimates the added air you need.

    Print the instructions & steady & follow them; play with it until you are sure you're doing everything right.

    Tell us what load-calcs you get; I think you'll be very surprised!
    Whole House Load-Calc
    I understand ACH=
    _____TIGHT __: 0.15
    SEMI-TIGHT __: 0.26
    _ AVERAGE __: 0.39
    SEMI-Loose __: 0.61
    ___ Loose ___: 0.82

    based on my use of Manual J8 abridged.

    Some residences with foam products ought to be < ~0.2
    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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