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  1. #1
    Join Date
    Sep 2012
    Posts
    7

    Confused Manual J Calculation without seeing the house?

    Hi: I am looking to replace my HVAC and duct work. I requested an estimate from a reputable and authorized Lennox dealer. The guy shows up and he presents me a one page Manual J calculation (report?) for my house. He's never been to my house but i suspect he was able to get information about my residence either from public records or google earth. I say Google Earth because he knew which windows were facing south, etc.

    All the other contractors who came to give estimates said they do the Manual J after they get the job to fine tune the exact tonage. All of themn said i needed a 3 ton system

    Question: Is it possible to do a Manual J without really looking at my house? Is this the norm or unusual?

    Thanks.

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,087
    Uh huh. And the satellite manual J has my 970 sq ft house at 1600. If someone sized based on that, I'd need a 3 ton. Sad. What other corners do they cut? Most the homeowner never knows about.

  3. #3
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,721
    Energy modeling software has default values. If it didn't, you'd "build" the model by entering every 2x4. (3 weeks later the model would be built...)

    So a really important step is to "true" the model to actual conditions (house size, leakage, insulation, and energy consumption). In looneys example, adjust model from 1600 to 970 sf.

    One problem you run into is people running the software don't get this. In NY, most HPwES contractors have no idea you can true TREAT because it's never been required, still isn't unless the project is to be financed via on bill recovery.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  4. #4
    Join Date
    Aug 2010
    Location
    West Monroe, LA
    Posts
    1,532
    Well that is a first for me to hear that contractor arrives at your home with a manual j load cal. Already done!

    I mean even with google earth given you the ablity to see the home does it tell the square footage, type of windows etc???

    What about the insulation in attic, walls and floor (it raised frame)? Temp the customer wants there home to be able to get too?

    Whenever i go out to a customers home, i do a load cal. Every time! Why not? Some will say what if you don't get the job? I say what if you do? You don't have to return and confirm sizing if done on the day of the visit.

    Also I can give the customer a price that does not change, peace of mind the equipment that my company will install will be proper sized and when they call to set up the job all the info., load cal etc.. are already done. So all we have to do is set up install date.

    Finally i can say that this approach has rewarded me with more jobs and saved the customer and myself a lot of time and it is my job. Sure you don't win them all so some time is lost but i know that i done my job.

  5. #5
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,721
    Phil's software pulls sf, year, and builds upon common assumptions. You can adjust all those things at the house, including orientation of greatest solar exposure.

    Also allows actual blower door number, and truing to actual energy consumption.

    My wish list, ESP and actual equipment extrapolating to what flow the duct can efficiently handle.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  6. #6
    Join Date
    Aug 2010
    Location
    West Monroe, LA
    Posts
    1,532
    Quote Originally Posted by tedkidd View Post
    Phil's software pulls sf, year, and builds upon common assumptions. You can adjust all those things at the house, including orientation of greatest solar exposure.

    Also allows actual blower door number, and truing to actual energy consumption.

    My wish list, ESP and actual equipment extrapolating to what flow the duct can efficiently handle.
    tedkidd- where do i go to find this software? I most review and see with my own eyes and try a few homes doing before and after i get on site to compare the numbers.

    If this is truly a good software this might be game changing if used properly.

  7. #7
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,274
    Quote Originally Posted by tikimaka View Post
    Hi: I am looking to replace my HVAC and duct work. I requested an estimate from a reputable and authorized Lennox dealer.
    The guy shows up and he presents me a one page Manual J calculation (report?) for my house. He's never been to my house but i suspect he was able to get information about my residence either from public records or google earth. I say Google Earth because he knew which windows were facing south, etc.

    All the other contractors who came to give estimates said they do the Manual J
    after they get the job to fine tune the exact tonage.

    All of them said i needed a 3 ton system

    Question: Is it possible to do a Manual J without really looking at my house? Is this the norm or unusual?

    Thanks.
    Yes, it is Possible, BUT,... ...

    I can perform a Manual J on your residence from afar by a few different methods.
    One is telepathy, which rarely works except on my Best_of_Luck days.

    One would only need
    city, state
    square footage - dimensions per floor
    R-value ceiling /walls
    U-value windows
    Air Change / Hour (ACH) [ house age]
    to estimate Block Load +/-20% for heating.

    Amount of Infiltration (ACH) would be / is a significant contributor to inaccuracies as experienced HVAC techs/designers well know.
    I believe that infiltration may be reasonably estimated based on age of house (if no renovations) for BID purpose.

    If one has performed > 2,000 calcuations in the local area, they are probably going to get_it_right in a quick review.

    A high estimate bid could be and are provided.

    I doubt that cooling load could be very accurate without a detailed review of windows
    unless photos (or orientation / size) and SHGC (or window purchase order)
    were provided by a responsible owner.

    I would NEVER provide a contract with final equipment selection and state equipment model numbers
    without a detailed Manual J calculation
    based on accurate definition of thermal building envelope parameters.

    A detailed load calc and duct work layout for heating & A/C could easily take 10X as long as a determining Block Load for heating.


    DID All of the contractors review existing condenser nameplate to determine 3-ton.?
    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
    Jul 2008
    Location
    Rochester NY
    Posts
    4,721
    BT, This reply break any rules?

    Quote Originally Posted by duckman06 View Post
    tedkidd- where do i go to find this software? I most review and see with my own eyes and try a few homes doing before and after i get on site to compare the numbers.

    If this is truly a good software this might be game changing if used properly.
    Yeah, imagine also having equipment run, od temp, and indoor temp history to triangulate...

    The top Home Performance companies in the country help target our Auditor user driven software development. We are well financed by 3 multi-billion dollar global companies with the common goal of, reducing cost, time frames, increasing accuracy, and making Home Performance mainstream worldwide. Branded versions of Auditor currently connect to financing portals and will be HPXML compliant.

    Auditor can be used free at:

    http://yourvirtualhvac.com/application/signin

    Use: demo@yourvirtualhvac.com

    Password: gizmo

    Good luck,
    Pj


    (from discussion Linkedin )

    An early video walk through which may be a good place to start:


    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  9. #9
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,721
    Bt felt posting that passed muster. So click the video link first to see how it works. Really cool.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  10. #10
    Join Date
    Sep 2009
    Location
    Arnold mo
    Posts
    3,965
    Have you played with the shading Ted? I couldn't get an answer from Phil regarding interior vs exterior shading. Have you tried setting the shading at 75% on a house which has the most windows facing westward? I was trying to model the effect of installing exterior solar screens.
    An answer without a question is meaningless.
    Information without understanding is useless.
    You can lead a horse to water............
    http://www.mohomeenergyaudits.com

  11. #11
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,274
    Quote Originally Posted by tipsrfine View Post
    Have you played with the shading Ted? I couldn't get an answer from Phil regarding interior vs exterior shading. Have you tried setting the shading at 75% on a house which has the most windows facing westward? I was trying to model the effect of installing exterior solar screens.
    DECREASE S.H.G.C.

    for More Shade effect
    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

  12. #12
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,721
    There is significant cost/learning curve in any modeling tool worth 2c. we have huge investment in understanding TREATs strengths and weaknesses, and working around them.

    I tracked results to TREAT. I know I can have high confidence in it realizing. That alone was a huge investment for me. So that's the software I have built confidence in.

    I also like the ability to use it for design. Phil's didn't allow that level of design or comparison when I looked at it. I'm sure it's much improved, but my interest is now moved to automatic realization tracking because doing it myself is such a royal PITA.

    I don't plan to embrace any tool change until realization is part of the tool.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

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