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  1. #1
    Join Date
    Aug 2012
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    1

    Confused Right Size for New Construction in Houston?

    We're building a new home that's been appraised for 4059 sq ft. We decided to have an inspector go out to the house and do what they do. During the inspection, they brought up that the installed unit is undersized. It's a Lennox 14ACX-060 16 SEER 5 ton external compressor.

    The inspector is claiming that we should have closer to an 8 ton unit. I requested the Manual J, but am still pretty lost. I've been doing a lot of reading today and am pretty convinced that the calculation is correct... But then again... I'm just going off of what I've read on the internet.

    I just want to make sure the unit is properly sized for our house. I don't want to end up stuck with a unit that's too small. Along with the manual J, I stuck a picture of the floor plan blueprint.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,704
    Inspectors don't know how to size A/Cs.

    You didn't tell u anything about the construction of the home. insulation values, orientation, windows, etc. So we can't tell you much about the sizing for it either.
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  3. #3
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,607
    For one i do not think the 14acx gets 16seer especially in the 5 ton. Unless the house is foamed insulation its highly unlikely to keep you comfortable in the heat of the day

  4. #4
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,596
    We need more info. Where are you building the home? If you're in the north, the 5 ton will run away with it. It might be a different story building in the south.

    One system for that size of a home, without zoning (in some form), is asking for comfort issues.

  5. #5
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,145
    Quote Originally Posted by George2 View Post
    We need more info. Where are you building the home? If you're in the north, the 5 ton will run away with it. It might be a different story building in the south.

    One system for that size of a home, without zoning (in some form), is asking for comfort issues.
    Anything over 2500sq ft typically gets 2 or more systems in Oklahoma, this may be different in Texas. Losses from long ductwork runs become an issue. As an added bonus if 1 systems goes down you can go to the other part of the house until repairs can be made. HVAC contractors are BUSY in summer and sometimes can't get out right away.

  6. #6
    Join Date
    Mar 2009
    Location
    Mount Holly, NC
    Posts
    3,006
    for comparison, my father's home in south Charlotte, NC where the humidity is high, and the temps sit around 100 in summer... has trees for shading, and the house is two story built in... 1906. ductwork installed in the 60's
    has a 2 ton system upstairs, and a 2.5 ton downstairs. total 4.5tons. it's a 4500 square foot home.
    if your house has vaulted ceilings, large windows facing south, black roofing, zero shade, and open crawlspace, with all equipment and ductwork in an uninsulated attic... with only a single floor for the full 4500 square feet, you could easily require double that tonnage. but the insulation, and the design of the house are all needed to make an estimate.
    bottom line, we cannot help you determine the load on your house, you have to get qualified estimators out to perform a total house load calculation.
    The TRUE highest cost system is the system not installed properly...
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  7. #7
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,596
    One of our estimators designed a large home with a single furnace and A/C using a 8 zone damper system.

    It has been some time since I've talked to him but he said they have never called back with any problems. I have a call into to get an update.

    I think the cost to run and maintain two systems offsets any "bonus". I've lived in my house 34 yrs. and have had 2 or 3 times the furnace (only, never with the A/C) needed some work.
    It was always addressed within hours of a call to service.

    P. S. I never have my equipment serviced (I do the condenser cleaning and filters) until it quits. That's just me. So far my luck, I would say, is pretty good.

  8. #8
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,145
    Zoning works great if it's done right. Some installers can barely get a non-zoned system done right (see wall of shame forum) , much less a zoned system. The odds of it being right are in your favor with having 2 systems. On a 4,000 sq ft house the ductwork sizing is critical to get all rooms (including the far ones) at an even temperature. The sling a flex here and there doesn't cut it on a large home with a single system.

  9. #9
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,233
    Quote Originally Posted by zombiefreak View Post
    We're building a new home that's been appraised for 4059 sq ft.

    I just want to make sure the unit is properly sized for our house. I don't want to end up stuck with a unit that's too small.
    Installation is going to have a huge impact on performance. AIR DISTRIBUTION DESIGN = Manuals D and T.
    Equipmen Selection = Manual S.
    http://contractingbusiness.com/ManualS/

    If the design based on all 4 ACCA Manuals is appropriate along with an excellent installation, there is a chance that one HVAC system "may be" adequate.
    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
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    If it was very well insualted, 5 tosn might be oversized.

    Widnows, shading, insulation are the major factors on sizing. Very unlikely it needs 8 tons unless it's a greenhouse, but with good shading (which isn't done in new ecclectic homes anymore) from trees and deep eaves, simple symmetrical home shape, and good insulation, you might need as little as 3 tons depending on where you live. I live in a moderately hot and humid location and only need 4 tons on 3200sqft 86y/o home. I have minimal insulation and tons of windows, but excellent shading form 40" downwards sloped eaves (Both things your almost never see on modern homes... lots of built in shade or windows... IMO we've mostly forgotten how to build good homes after WWII chasing after profits and low $/sqft. Sorry I can't keep the old hose snob out of these discussions).

    With a home over 3000sqft, I'd definitely want 2 systems for the best comfort. Also, spaces used for sleeping vs entertaining & cooking have very different termperature requirements and laods. A home that large will probably be imbalanced frequently no matter how perfect hte ductowrk is. However, a properly sized system will run loner and allow more even temperatures.

  11. #11
    Join Date
    May 2002
    Location
    Houston Texas
    Posts
    6,316
    Op I have homes in Houston over 4000 sq.ft. with 2-tons systems and some with 7.5-tons proper sizing can only be determined with a proper load calculation and as stated the most critical component will be your ductwork.

    Regardless of the design of the house either two systems or a properly designed zoned system will be required. If one of the normal RNC companies are doing the install your comfort will be terrible. There are very few companies in Houston that can install a system in a home the size of yours and provide you with true comfort and efficiency. There is not one of the usual RNC company's that can install a ducts system or zoned system that will deliver proper airflow to all rooms off a single system in a 4000 sq.ft. home.

  12. #12
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
    Posts
    2,596
    UPDATE.........I spoke with one of our designers regarding the home with the 8 zones.

    The home is (only!) 3,600 sq. ft. 2-story with a full basement (I forgot to ask if it was a walkout basement), 5 ton A/C with 8 zones. The house is located in the midwest, so we don't get the heat you do. Never a problem.

    It sound like you'll need two system. You can still zone those as you like.

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