Manual J Load Calculator

Building Info

Wall Assembly

Fenestration

Other Loads

Step 1 of 4

Building Information

Project details, dimensions, and design temperature conditions

Project Name

Location / ZIP Code

Construction Type

Total Conditioned Floor Area (sq ft)

Number of Stories

Avg. Ceiling Height (ft)

Number of Bedrooms

Garage

Design Temperatures

Outdoor Cooling Design Temp (°F)

Outdoor Heating Design Temp (°F)

Indoor Cooling Setpoint (°F)

Indoor Heating Setpoint (°F)

Humidity

Indoor Relative Humidity (%)

Outdoor Wet Bulb — Cooling Design (°F)

Step 2 of 4

Wall Assembly

Define each exterior wall segment, construction type, and opening areas

Wall ID	Orientation	Construction	R-Value	Length (ft)	Height (ft)	Window Area (sq ft)	Door Area (sq ft)	Net Wall Area	Heat Loss (BTU/hr)

Step 3 of 4

Fenestration — Windows & Doors

Enter all glazing and opaque door units with U-values and SHGC ratings

Location / Label	Type	Width (in)	Height (in)	Qty	U-Value	SHGC	Orientation	Heat Gain (BTU/hr)	Heat Loss (BTU/hr)

Step 4 of 4

Other Loads

Ceiling, floor, infiltration, ventilation, and internal gains

Roof / Ceiling

Ceiling Type

Ceiling Area (sq ft)

Ceiling R-Value

Floor

Floor Type

Floor R-Value

Note

Slab on grade typically uses R-0. Crawl space floors should be R-19 to R-30. Over garage R-30 minimum.

Infiltration

Building Tightness

Air Changes per Hour (ACH)

Auto-filled from tightness selection; you may override

Ventilation

Ventilation Type

Required Ventilation CFM

ASHRAE 62.2 = 0.03 × floor area + 7.5 × (bedrooms + 1)

Internal Gains (used for cooling load only)

Lighting (watts)

Default = floor area × 1.5 W

Plug Loads / Appliances (watts)

Default = floor area × 2.0 W

Occupants

230 BTU/hr sensible + 195 BTU/hr latent per person

Manual J Load Calculator

Building Information

Wall Assembly

Fenestration — Windows & Doors

Other Loads

Load Breakdown by Component