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Thread: Vent algorithm

  1. #1
    Join Date
    Aug 2011
    Posts
    2

    Confused Vent algorithm

    what is the formula to determine return and supply grilles/ducts for a residential 1200SQ' house in CA. NO a/c w a new 95% variable speed furnace???

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,704
    Room by room load calc, Which will give you the CFM you need per room. Then you can use manual D to determine what FR to use to size your duct work, and manual t to determine what grilles and registers to use.
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    How many times must one fix something before it is fixed?

  3. #3
    Join Date
    Aug 2011
    Posts
    2

    Hmm uummmmmm......

    I think I was sick that day at school. Can you help me being a little more specific? lol

  4. #4
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,283
    You must start with knowing how much heat the house is expected to gain on what's called a "design day" for your region. Get a copy of Manual J and read through it. Manual D for duct design. Manual S for equipment selection methods.

    This is not something you just "wing it" on and hope for the best. Do it right or hire someone who can. Especially in California, with duct leakage testing and Title 24.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,704
    Do a search here on manual J, and also go to ACCA's website.
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    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  6. #6
    Join Date
    Jul 2011
    Location
    Waxahachie TX/stuck in Santa Clara CA
    Posts
    53
    What part of CA (city/climate zone)?

    Not a pro, so please don't take this as technical advice:
    If you are trying to do this yourself, it can be a very, very long road and although it may not seem like it now, winter is coming. This site doesn't allow DIY, so you won't get much real help here, anyway. Be careful, from what I seen, the "other" forums geared toward HVAC & DIY contain a lot of confusion and dis-information... call a pro
    If you just want to understand what your contractor is proposing/doing, then reading manual J and D sounds like a good start. They're not cheap, though.

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