Thermal Resistance Calculator
Calculate thermal resistance and R-value for insulation materials.
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Thermal resistance measures how well a material resists heat flow. Higher R-values mean better insulation. This calculator converts between metric R-value (m²·K/W) and imperial R-value (the number on insulation packaging in the US). It also calculates actual heat flow through a specific area, which is essential for HVAC load calculations.
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Frequently asked questions
R-value = thickness / conductivity = 0.1 / 0.04 = 2.5 m²·K/W, or R-14.2 in imperial units. Standard wall insulation is about this thickness.
Multiply metric R-value (m²·K/W) by 5.678 to get imperial R-value. So R-2.5 metric = R-14.2 imperial. US insulation is sold by imperial R-value.
Fiberglass conductivity (0.04 W/m·K) is 42.5 times lower than concrete (1.7 W/m·K). To match 10 cm of fiberglass, you would need 4.25 meters of concrete.
Heat flow = ΔT / R. Through 10 m² of R-14.2 wall with 20°C temperature difference: Q = 20 / 0.25 = 80 watts. Over 24 hours that is 1.92 kWh.
US Department of Energy recommends R-38 to R-60 for attics (climate dependent). That is about 25-40 cm of fiberglass batts. R-38 reduces heat flow to about 0.5 W/m² per degree of temperature difference.