Building Envelope Heat Loss Simulator

Insulation

Material

Thickness 100 mm

Weather

Outdoor temperature 0 °C

Wind speed 5 m/s

Indoor temperature (fixed) 21 °C

Live Readouts

Wall U-value

— W/m²K

Heat loss power (100 m² wall)

— kW

Est. heating-season cost

— $

How it works

Heat crosses a wall by conduction through each layer and by convection at the two surfaces. For flat layers in series the resistances simply add (Fourier's law of conduction, steady state):

R_total = 1/h_in + Σ(t_layer / k_layer) + 1/h_out
U = 1 / R_total            [W/m²K]
Q = U · A · (T_in − T_out)  [W]

Layers modeled here (indoor → outdoor): 12.5 mm gypsum board (k=0.17), the insulation you choose, and a 100 mm brick veneer (k=0.77). Interior film coefficient h_in = 7.7 W/m²K. Exterior film coefficient rises with wind speed v via the McAdams correlation h_out = 5.8 + 4.1·v, so a windy wall sheds heat faster even with identical insulation.

Material / thickness — sets the insulation layer's thermal resistance t/k; a lower k or thicker layer means a lower U-value.
Outdoor temperature — sets the driving ΔT = T_in − T_out across the wall.
Wind speed — raises the exterior convection coefficient h_out, thinning the outside boundary layer.

The 3D house recolors from blue (well insulated, low U) to red (poorly insulated, high U), and the glowing particles crossing the wall cross-section on the right represent the conducted heat flux — their speed and density scale with Q.

Heat flow (indoor → outdoor) Insulation layer

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