BTU inch per hour square foot Fahrenheit
Thermal conductivityexact by definition
The BTU inch per hour square foot Fahrenheit is 0.1442278891 W/(m·K). It is the North American insulation k-value: heat per hour through one square foot of material one inch thick, per degree of temperature difference. Fibreglass batt is about 0.32, extruded polystyrene 0.20.
Watch out: Do not confuse it with BTU/(h·ft·°F), which is the same quantity per foot rather than per inch and is therefore twelve times larger. Both are in this catalog. Insulation is quoted in the inch form; pipe and metal conductivity in the foot form.
| 1 BTU·in/(h·ft²·°F) | 0.14422789 W/(m·K) |
The inch in the numerator is what makes it usable in the trade. R-value per inch is simply 1 divided by this number, so a k of 0.20 is R-5 per inch and the whole US insulation market can be discussed without a calculator.