Heat Loss Calculator
Estimate heat loss through walls, windows, roofs, and floors using the Q = U × A × ΔT method. Perfect for energy audits and HVAC sizing.
°F
°F
Surface Areas (sq ft)
ft²
ft²
ft²
ft²
U-Values (BTU/hr·ft²·°F)
U
R-12.5 (typical insulated wall)
U
R-2 (double-pane)
U
R-25 (attached insulation)
U
R-20 (insulated floor)
ACH
0.5 = tight, 1.0 = average, 2.0+ = leaky
ft³
(Area × Ceiling Height)
⚠️
Total Heat Loss
—
BTU/hr
—
Envelope Loss
—
BTU/hr
Infiltration Loss
—
BTU/hr
Total Area
—
sq ft
ΔT
—
°F
Calculation Breakdown
Step-by-step heat loss analysis
Heat Loss Formulas
Key equations used in building science
Energy Efficiency Tips
Reduce heat loss in your building
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Engineering Disclaimer: This calculator provides estimates based on simplified models. For accurate HVAC sizing and energy audits, consult a professional engineer and perform a detailed energy analysis.