Results 1 to 3 of 3
  1. #1
    Join Date
    Jul 2009
    Location
    South Carolina
    Posts
    3,197

    Manual J formulas?

    I've got all the software I need but what I'm looking for is a book or something where I can find the actual formulas & factors used for calculations. What I need is a form sheet where I put my sq. ft. walls,widows etc..& then gives me the factors needed to multiply where I have to calculate each item seperately instead of the program doing it for me. Years ago before computers I had a book that I used to do my load calculations with .
    I've been learning a little javascript & I'd like to give it a try but I need to be able to do a calculation manually before I begin.
    Any ideas?

  2. #2
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Quote Originally Posted by garyed View Post
    I've got all the software I need but what I'm looking for is a book or something where I can find the actual formulas & factors used for calculations. What I need is a form sheet where I put my sq. ft. walls,widows etc..& then gives me the factors needed to multiply where I have to calculate each item seperately instead of the program doing it for me. Years ago before computers I had a book that I used to do my load calculations with .
    I've been learning a little javascript & I'd like to give it a try but I need to be able to do a calculation manually before I begin.
    Any ideas?
    www.acca.org

  3. #3
    Join Date
    Sep 2002
    Location
    I don't know
    Posts
    2,903
    Q Loss (BTUs) = Surface area x (indoor - outdoor design temp) / Effective R-value*

    *You have to take thermal bridging through studs into consideration - an R12 wall has a real thermal resistance value of less than R12.

    The R value of basic wood double pane windows is around 1.7 if I remember correctly.

    For air leakage:

    Q sensible (Btus) = 1.09 x airflow CFMs x (indoor - outdoor design temp)

    A blower door test is required to measure leakage.

    I don't know the formula for latent heat loss off the top of my head.

    Don't worry about passive solar heat gain for heating since the system has to be sized for design conditions. (No sunlight)

    For making a template I recommend excel.
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event