Performed Manual J, and can’t believe the results
I now understand why HVAC folks flub Manual-J to make themselves believe the output.
I’m building a 2400 sq/ft home Charleston SC.
I’ve input all my calculations into coolcalc.com manual j calculator and the average btu/h that came out was 6,731 btuh. The average * 1.3 was 8,750.
Cooling Loads (dont fully understand these)
Area: 2,635 (i must have actually over estimated here)
Heating Loss: 15,899
The house details are:
2×6 external 16″ oc, R21 walls
Windows are u-factor of .28 and SHGC of .19
Encapsulated Attic, with spray foam
indoor cooling: 75
indoor heating: 70
outside design cooling temp: 91
outside design heating temp: 28
I set the ACH to 3 changes per hour. I hope to get it tighter and I am contracting someone to do a blower door test (even though code requires it). 3 seemed safe?
The HVAC contractors I’m sure are using rule of thumb to size the tonnage which I think they put at either 2 or 3 tons. Either way, 2 tons = 24,000 btu/h and 3 = 36,000 btu/h?
I feel I must be missing something. a 2400 sqft house and 8750btu/h?
i’m trying to understand my cooling and heating load in order to figure out what size HVAC (to check contractors) i need in order to determine my electricity needs to heat and cool in order to size my pv array. I’ve completely flubbed my manual-j, the software is wrong, or I am mis-understanding the numbers is all I can think of.
Do these numbers look crazy?
Thanks for any assistance!