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Re: [Phys-l] Insulation R-value

On Feb 17, 2006, at 4:07 PM, ALVIN BACHMAN wrote:

Correction: Units of R are F-deg (of temp difference) per (BTU/hour/sq-ft)

So R-19 means that a difference of 19 Fahrenheit degrees across the
surfaces
of this material will produce a transfer rate of 1 BTU/hour per square foot
of surface area.
R-30 is better because it requires a 30 degree difference to produce the
same energy transfer rate.

Note that this may not reflect the over-all (internal air to external
environment) transfer, due to air boundary layers, convection , radiation,
etc.

Are you sure about the last sentence, Al? The only reason to exclude the non-conductive losses would be to make determinations of R more difficult. I suspect that the BTU refers to all losses, under some standard conditions. But I might be wrong.

Ludwik Kowalski
Let the perfect not be the enemy of the good.