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  1. #27
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Originally posted by trane
    One never knows how many CFM are required for every room because it constantly changes and is always a guess. As the sun moves around the home and the wind changes direction so does the required CFM's.
    Thats what zoning is for.
    If more government is the answer, then it's a really stupid question.

  2. #28
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,001

    Exclamation OLD Challenges !

    Originally posted by trane
    Originally posted by cem-bsee
    just what makes a home built in 1948 different from one built in 1998 or in 2004 with respect to knowing about the construction?
    Your right, there may not be any difference in the homes you owned. That would all depend on the contractors that built them and there interest in seeing that no corners are cut.

    Most manual J calculations are done by guessing on certain factors when dealing with an existing home and it gets worse the older the home is to come up with the closest actual inputs.
    WHY guess? Just LOOK AT the house!
    Look at the FULL cross section of the wall.
    Dig a little Deeper!

    When you know what you are looking at, it is NOT A Guess.
    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

  3. #29
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    all of my houses have been built differently! but, the constructions seemed to be well covered in my older (before 1995 ) editions of Manual J.

    Not well covered is my current house with LOTS of shade & one attic with forced ventilation by a powered roof vent.

    but then, I looked at the wall, attic, slab insulation, or lack there of; the window & door construction & fit, etc.

    BTW, my 1974 dbl hung wood windows fit TIGHT -- I would not even consider changing them to the galling, saging vinyl windows!! the only ones needing painting or glazing were the 4 in the garage without storms --


    harvest rainwater,make SHADE,R75/50/30= roof/wall/floor, use HVAC mastic,caulk all wall seams!

  4. #30
    Join Date
    Oct 2005
    Posts
    88
    Originally posted by jacquelynn
    And chapmanf -- do you know anyone who'd like to review my utilities bills (for pay of course). I'm definitely not the person to do it.
    Sorry I didn't see this earlier. This is something I've done for a few people informally (I'm a computer geek, not an HVAC installer, though I did HVAC controls software in a past life). I cannot recommend using the figure in place of Manual J, because J is the recognized procedure, but some people have found it an interesting sanity check on the Manual J result, and that's all I would suggest it for. If on that understanding you think that review would be worth something to you, feel free to decide how much and e-mail me. Best if you can confirm your gas bills do contain all the information I mentioned, including heating degree days for the billing period. The gas co here only started including that a few years ago; before that one could get the figures from the weather service, but the calendar months and billing periods wouldn't match so the line fit would be worse, and it was more trouble than it was worth. Easiest if you're willing to keyboard the numbers from the bills. On the left of the at sign, chap, on the right, anastigmatix dot net, if you're interested. Thanks for asking.

    -Chap

  5. #31
    chap --

    I appreciate your suggesting it. Let me think about it; I may be giving up on the whole idea of a new system anyway.

    Thanks again.

  6. #32
    Join Date
    Oct 2005
    Posts
    88

    wotta coincidence

    In another thread, behemoth60 just posted a link to a Canadian site that explains using utility bills for sizing:

    http://www.cmhc-schl.gc.ca/en/burema..._048.cfm#bills

    A little less thorough than the way I've been doing it (I like to use more than 3 mos of bills, fit a line, and determine the nonheat usage from the data instead of estimating it), and the examples are all metric, but definitely covers the basic idea.

  7. #33
    Thanks again! I'll check it out.

  8. #34
    Join Date
    Apr 2004
    Location
    Bartlett, IL
    Posts
    6,619
    I only do heat loads on new construction, this is where manual J comes into an accurate sizing situatuion, but I am usually 98% accurate on my own sizing before I to a heat load calc.

    On replacements I look at the obvious infiltration issues and size equipment to MY discretion, I would ONLY do a heat load on a replacement IF the customer promises to use MY company, otherwise they would have to pay an extra fee for this service, the rest of you can waste your time if you consider it NOT valuable.

  9. #35
    Join Date
    Oct 2005
    Posts
    88
    the rest of you can waste your time if you consider it NOT valuable.
    Hmm. Looks to me like the OP has been using "would you do a load calc" as a screening question in selecting a contractor--not asking them all to come out and do it--and has clearly expressed willingness to pay for the service. I might not see where the wasting time comes in.

    From the Canadian link above, it looks like it might be fairly common for Canadian contractors to just put a price on load calc as a standalone service and do it for anyone whose money is green (or whatever color a cdn$ is these days).

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