Posted by **James** on Thursday, July 19, 2012 at 4:15pm.

The thermal conductivity of fiberglass batting, which is 8.9 in thick, is 8.6 10-6 BTU/(ft °F s). What is the R value (in ft2 °F h/BTU)?

The R value is 24 ft^2 Fh/BTU. How do I get this answer?

- Physics -
**drwls**, Thursday, July 19, 2012 at 6:54pm
R is the reciprocal of the amount of BTU of heat transfered across 1 ft^2 in 1 hour with a temperature difference of 1 F.

1/R = 8.6*10^-6*3600 s*(1.0 degF)/(8.9/12 ft)

R = 24 ft^2*degF*h/BTU

- Physics -
**James**, Thursday, July 19, 2012 at 10:53pm
Thank you!

Could you write out just the basic equation that you used?

- Physics -
**James**, Thursday, July 19, 2012 at 10:57pm
The equation I found in my text book doesn't mention time being a factor when calculating R.

I have R= L/k

where L is length and k is thermal conductivity.

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