Manual J Load Calculator
Calculate heating and cooling loads for residential buildings
Quick Setup
New Construction
Existing Home
Older Home (Pre-1980)
Climate Zone:
Hot-Humid (South, Southeast)
Hot-Dry (Southwest)
Mixed-Humid (Mid-Atlantic, Ohio Valley)
Mixed-Dry (Central Plains)
Cold (Northern States)
Very Cold (Northern Border, Mountains)
Basic Information
Floor Area (sq ft):
Total conditioned living space
Ceiling Height (ft):
Number of People:
Main Window Direction:
Mostly South
Mostly North
Mostly East
Mostly West
Mixed/Multiple
Building Details
Windows (% of wall area):
Typical: 10-20%
Insulation Level:
Poor (Minimal/Old)
Average (Code Minimum)
Good (Above Code)
Excellent (High Performance)
Window Type:
Single Pane
Double Pane
Double Pane Low-E
Triple Pane
Foundation Type:
Slab on Grade
Basement
Crawlspace
Show Advanced Settings
Advanced Settings
Climate Settings (Override Defaults)
Winter Design Temp (掳F):
Set by climate zone, can override here
Summer Design Temp (掳F):
Set by climate zone, can override here
Summer Humidity Ratio (grains/lb):
Set by climate zone, can override here
Air Changes per Hour:
Infiltration rate: 0.1-1.0
Building Areas (Auto-calculated)
Wall Area (sq ft):
Auto-calculated from floor area
Window Area (sq ft):
Auto-calculated from wall % setting
Roof Area (sq ft):
Auto-calculated with pitch factor
Door Area (sq ft):
Typical: 20-40 sq ft
Building Performance Values
Wall U-Value (Btu/hr路sq ft路掳F):
Set by insulation level
Roof U-Value (Btu/hr路sq ft路掳F):
Set by insulation level
Window U-Value (Btu/hr路sq ft路掳F):
Set by window type
Window SHGC:
Solar Heat Gain Coefficient
Floor U-Value (Btu/hr路sq ft路掳F):
Set by insulation level
Mechanical Ventilation (CFM):
Additional fresh air system
Internal Heat Gains (Auto-calculated)
Appliance Load (Watts):
Based on floor area
Lighting Load (Watts):
Based on floor area
Calculate Load
Calculation Results
Heating Load
0 Btu/hr
Cooling Load (Sensible)
0 Btu/hr
Cooling Load (Latent)
0 Btu/hr
Total Cooling Load
0 Btu/hr
Load Breakdown