ask 2 contractors and you'll get 3 answers...
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  1. #1
    Join Date
    Apr 2006
    Location
    Austin, TX
    Posts
    3
    The question at the bottom of this long post is: Who is crazier, Contractor 1 or Contractor 2?

    Cooling environment:
    1982 2-story 1750 sq ft house in northwest Austin, TX. Living, master, kitchen on top floor so thermostat is on top floor. Slab, no basement, you just enter the house using stairs... (it's weird, I know).

    House is shaded by trees, hillside, and neighboring houses. No windows get very much direct sun -- mostly shaded by trees.

    Current A/C: 1985 GE 4-ton SEER 6 and pilot lit gas furnace.

    I called 3 different contractors, two that do the city energy audit thing and a third guy who doesn't in case I could only afford HVAC replacement.

    About 40 ft of ducting is bad and the insulation is in dire need of revamping (R-30 is the city standard for rebates). They all said this so I'm definitely fixing that stuff.

    HVAC recommendations
    --------------------
    Contractor 1:
    says that since there's a 4 ton in there and it looks to him that the in-wall duct is set up for that, he recommends a 3.5 ton, even though 3 ton is what the square footage calc should yield (600 sq ft per ton, city recommendations). The reason given is so that the 55 degree air from a 3 ton blower doesn't sit there in the bigger 4-ton size channel heating up.

    Contractor 2:
    says that since the house is so well shaded, the first floor is completely covered, thermostat is upstairs, etc. he recommends a 2.5 ton unit. I tell him what Contractor 1 said about air movement and he said he thought the in-wall duct looked to him sized for smaller than a 4-ton. He also thought a larger unit would go on and off all the time.

    Contractor 3:
    didn't bring a ladder. So I told him about the duct work and insulation and he said he'd quote me on that and bid a 3.5 and a 2.5 ton system.

    Contractor 1 swears by Carrier, Contractor 2 swears by Lennox, but they'll both install most of the major brands. Contractor 3 will install pretty much whatever you want.


    My question is: Is Contractor 2 crazy and potentially severely underpowering the system or is Contractor 1 crazy and potentially overpowering the system?

    Thanks for ANY help!!!
    -l

  2. #2
    Join Date
    Apr 2006
    Posts
    35

    I live in Southern New Mexico and I have 1980 sq ft. Two contractors tell me 5 Ton (one has 27 years in the business), I have one telling me a 4 ton, and 1(40 years to include duct design etc) telling me a 3.5 - 4 Ton. Who knows. I want to get them all in one romm and let them argue with eachother while i decide who to believe.


    Good luck
    Greg

  3. #3
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Sounds to me like you need to find another contrctor. One that will perform a Manual J load calculation and actually evaluate your duct system.

    Someone using rules of thumb sizing based on square feet per ton, and/or someone that offers 2 different capacities of systems, is to be avoided...
    If more government is the answer, then it's a really stupid question.

  4. #4
    the problem with residential contractors is that 95 % dont know.
    also you cant look at a duct system and guess.
    each main has to be calculated, and that will only tell you how much capacity the duct will carry, it doesnt tell you if the duct system is the proper size for the home and in most cases and i cant fiquere it out but most are way off.
    i have yet to find a home that the duct design is correct.
    it goes to show that a/c is more than a mechanics game.
    hey engineers dont even have enough brains to design a unit were the panels come off not to mention goodman stacking everything on a plate with just enough room to get your hand in there to put a meter. come on guys wake up.

  5. #5
    Join Date
    May 2002
    Location
    Houston Texas
    Posts
    6,315
    Simple answer contact Michael Scheer owner All-Year A/C. Only problem I have is he sells Trane.

    Seriously I worked in Austin from 1995 to 1999 and the majority of the major players in the City rebate program were worthless. In order to do the work required by the city to qualify for the program you had to do the work too cheap to do quality work.

    Michael is a TU graduate Architect and migrated to A/C and he does outstanding work.

  6. #6
    Join Date
    Apr 2006
    Location
    Austin, TX
    Posts
    3
    Originally posted by mark beiser
    Sounds to me like you need to find another contrctor. One that will perform a Manual J load calculation and actually evaluate your duct system.
    Can you do a Manual J if you've got a length of duct with the inner lining exposed to attic air? I've got one in this new-to-me house that looks like someone took a razor blade to it. hehehe Just one of those ancient ducts splitting at the seams.

    Sorry, I'm just not very aware of what's involved in such a process. (Googling it as I type this).

    -l

  7. #7
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,225

    Talking Sure, It's Simple

    Originally posted by gkck
    Southern New Mexico
    1980 sq ft.

    Who knows.
    3.8475667548 Tons are required!
    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
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Originally posted by luyseyal
    Originally posted by mark beiser
    Sounds to me like you need to find another contrctor. One that will perform a Manual J load calculation and actually evaluate your duct system.
    Can you do a Manual J if you've got a length of duct with the inner lining exposed to attic air? I've got one in this new-to-me house that looks like someone took a razor blade to it. hehehe Just one of those ancient ducts splitting at the seams.

    Sorry, I'm just not very aware of what's involved in such a process. (Googling it as I type this).

    -l
    The Manual J load calculation is for determining the heat loss/gain of the home. Manual D is for designing the duct system.

    It sounds like what you have is ducts that need to be replaced though. Is it flex duct that has a gray vynal jacket around it?
    All that exposed inner liner you have will cost you a fortune in energy...
    If more government is the answer, then it's a really stupid question.

  9. #9
    Join Date
    Apr 2006
    Location
    Austin, TX
    Posts
    3
    Originally posted by mark beiser
    The Manual J load calculation is for determining the heat loss/gain of the home. Manual D is for designing the duct system.

    It sounds like what you have is ducts that need to be replaced though. Is it flex duct that has a gray vynal jacket around it?
    All that exposed inner liner you have will cost you a fortune in energy...
    OK, I'm not too interested in a completely redesigned duct system. Both of them said the in-wall stuff is probably fine and pretty expensive to replace... do I still need a Manual D?

    Yeah, it's that old grey stuff that ruptures easily. Most of the ducting is newer, but there is about 40' of that bad duct in the attic that needs replacing. I absolutely plan to replace that.

    Should I call those guys back and have them do a Manual J? Or should I just call other people? I was thinking of telling them since the estimates were all over the map I wanted the by-the-book Manual J eval. Do I really need a Manual D, too?

    Thanks for all your help, everyone!
    -l

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