Series conduction resistances add; thickness and conductivity determine each resistance.
Thermal Resistance Circuits gives representative brick k=0.7 and insulation k=0.07 W/(m·K).
MIT · Thermal resistanceA blanket works both ways.: sources & model
Open a house wall. Swap its added layer, make it thicker, and reverse the temperatures to see why insulation helps in winter and summer.
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thermal-insulation-1 · content 1 · setup format 1What supports the explanation?
A slab model requires specified boundary temperatures and assumptions.
Steady, one-dimensional, constant-property conduction without internal generation.
MIT · Steady conductionUS thermal insulance converts to SI by 0.1761102.
SI Appendix B.9, thermal insulance.
NIST · Unit conversionInsulated and control cups can be compared by water-temperature change.
Published activity allows a cold-water-only investigation. The simplified adaptation below has not been trialed.
NASA/JPL · Mars ThermosWhat this model assumes
- Steady one-dimensional conduction through equal-area homogeneous layers with constant properties and perfect contact.
- The house is context; watts apply only to the stated 1 m² wall-face section. No whole-building energy, heating-bill or construction-code advice.
- Arrows show net heat-transfer direction and comparative magnitude, not physical heat particles or a transient cooling simulation. Electrical insulation is a separate property.
- Layer resistances add: Area-normalized resistance is R=L/k in m²·K/W. The 10 cm base brick layer and added layer are in series, so their resistances add. For the 1 m² calculation area, Q̇=A(T_inner−T_outer)/R_total.
- Know the boundary temperatures: Controls set wall-face temperatures, not indoor/outdoor air temperatures. The model omits surface convection, radiation, framing, windows and drafts. It describes a settled one-dimensional heat flow, not how quickly a room cools.
- Metric and US R-values differ: One US R unit equals 0.1761102 m²·K/W. The metric display gives RSI; imperial gives US R. The representative conductivities, 0.7 W/(m·K) for brick and 0.07 for generic insulation, are textbook examples, not product specifications.
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