Results 1 to 3 of 3
Thread: Manual J formulas?
09-22-2009, 12:03 AM #1
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 .
09-22-2009, 12:07 AM #2Banned
- Join Date
- Aug 2002
- Office and warehouse in both Crystal River & New Port Richey ,FL
09-22-2009, 02:31 AM #3Regular Guest
- Join Date
- Sep 2002
- I don't know
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.