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HVAC Equipment Sizing Calculator — Manual J Load Estimate
Estimates residential heating and cooling loads using the Manual J simplified methodology to properly size HVAC equipment. Enter your home's characteristics to calculate BTU/hr requirements.
Building Envelope
Conditioned Floor Area (sq ft)
Average Ceiling Height (ft)
Number of Stories
1 Story
2 Stories
3 Stories
Wall Insulation R-Value
R-11 (2×4 minimal)
R-13 (2×4 standard)
R-19 (2×6 standard)
R-21 (2×6 high)
R-25 (advanced)
Ceiling/Attic Insulation R-Value
R-19 (minimal)
R-30 (standard)
R-38 (recommended)
R-49 (high performance)
R-60 (super insulated)
Floor/Crawlspace Insulation R-Value
R-0 (slab on grade)
R-11 (minimal)
R-19 (standard)
R-30 (high)
Windows & Doors
Total Window Area (sq ft)
Window Type / U-Factor
Single Pane (U=1.1)
Double Pane Clear (U=0.65)
Double Pane Low-E (U=0.40)
Triple Pane Low-E (U=0.30)
High-Performance Triple (U=0.22)
Window SHGC (Solar Heat Gain Coefficient)
0.87 (single pane)
0.70 (clear double)
0.40 (low-e standard)
0.25 (low-e low gain)
0.20 (spectrally selective)
Dominant Window Orientation
North (minimal solar)
East/West
South (standard)
Mixed/All directions
Exterior Door Area (sq ft)
Door Type / U-Factor
Wood Solid Core (U=0.60)
Insulated Steel (U=0.40)
Insulated Fiberglass (U=0.30)
High-Performance (U=0.20)
Infiltration & Internal Gains
Air Leakage / Infiltration Level
Tight (0.25 ACH) — New construction
Average (0.50 ACH) — Typical
Leaky (0.75 ACH) — Older home
Very Leaky (1.0 ACH) — Pre-1980
Number of Occupants
Lighting Load (W/sq ft)
0.5 W/ft² (all LED)
1.0 W/ft² (mixed)
1.5 W/ft² (older fixtures)
2.0 W/ft² (incandescent)
Appliance/Equipment Load (BTU/hr)
Duct Location
Conditioned space (no loss)
Sealed attic/crawlspace
Unconditioned attic (standard)
Unconditioned attic (leaky)
House Construction Type
Well-shaded / heavy mass
Standard frame construction
Open / light construction
Mobile / manufactured home
Calculate HVAC Load
Manual J Load Estimate Results
Assumptions & References
Based on ACCA Manual J 8th Edition simplified residential load calculation methodology
