Thermal resistance of plywood

It is called R factor.

There are exterior panels that are made specifically for this purpose. The best in the world are made from hemp fiber in a country that grows thousands of acres of non-drug hemp strains because the fiber is very strong (the strongest plant fiber) The best exterior home construction panels are hemp.

They also mean that:

"No pine tree forests were cleared in the making of these homes".

America is stupid sometimes. Hemp laws are one such example.

Engineers call it "thermal conductivity."

John

=A0 =A0 ...Jim Thompson

=A0 | =A0 =A0mens =A0 =A0 |

=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

=A0 =A0 =A0 |

plywood 0.13 W/mK

What do you think the "R factor" value is based on?

We call it science regardless of the discipline.

Shucks! That was what was giving me the pain and agony... converting Btu's per fortnight, etc ;-)

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
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| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
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 I love to cook with wine     Sometimes I even put it in the food

R value is defined here:

For 3/4" the R value appears to be 0.93 delta °F x ft^2 x hour/Btu

This page:

Has 0.125" single pane glass with an R value of 0.89. So your plywood and glass are pretty close to even.

I'll leave the units conversion up to you for actual values.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
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There is no place like 127.0.0.1

Perhaps,but that will cut no ice when shopping for thermal insulation panels at Home Depot or Lowes.

Milli-Kelvin?? Yes, that is a useable unit but isn't watts per Kelvin a bit more practical and conventional?

Here are some measurements from a light-bulb-heated food dryer with its vents closed: Turned on a 40W bulb at 3pm, 75F. At 4:20, with 90F near the middle of the box, turned off 40W bulb, turned on 60W bulb. At 5:20, with 108F near the middle, turned off 60W bulb, turned on 40W bulb. At

10pm, 94F near the middle. This box is about 10"x11"x28" inside, or twice the volume of your 8"x11"x18" box. 50% of its surface is 3/4" wood, 35% is 1/8" masonite, and the rest is window glass.

In case that this is not a troll, look at it (using a fixed width font like Courier New):

W 0.13 ---------- m K

Paul

Idiot. NOTHING "milli" uses a capital M. It was also inappropriate to be the first word in your non-sentence, if not for that reason alone.

Perhaps "Are you saying milli-Kelvin?"

Does Home Depot specify the R-value of their plywood?

John

OK, what's the relationship between R factor and thermal conductivity?

John

m = meter.

John

I have some liking to page 1572 of the 43rd edition of the "CRC Handbook", "Thermal Conductivity of Wood Across the Grain at Various Moisture Content Values".

The moisture content values vary mainly with type of wood tested, mostly from 9 to 14 %. Thermal conductivity in BTU/hour through 1 inch thickness of 1 square foot with 1 degree F temperature difference has 90% of figures in the range of .73 to 1.39, and I would like to say as a result moderately-conservatively .8, more-usual .9.

This box, with inside surface area (assuming above dimensions are external) of 6 * 6.5 * 9.5 * 16.5 /12^3) about 3.54 square feet, with 3/4 inch thickness, has thermal resistance (within itself, as opposed to thermal resistance of adjacent air) of maybe 3/4 divided by 3.54 divided by .8-.9 watts/F, or roughly (give or take) 1/4 degree F per watt.

Thermal resistance drops bigtime, to extent where I consider likely the thermal resistance of the air inside and just outside the box.

I know someone who, at my advice, did an experiment measuring temperature of a metal-cased device in open air and in a "largish shoebox", with readings taken over time to verify temperature stabilization. As best as I remember at this moment, the "largish shoebox" including air stagnated near its inside and outside surfaces had thermal resistance around 2-2.5 degrees F per watt, probably closer to

2 - apparently mostly from impairing convection of air around the device that was tested. The device being tested had overall dimensions close to those of a "double thickness cigarette pack".

- Don Klipstein ( snipped-for-privacy@misty.com)

Larkin = dope.

Archie = Celibate asshole

Do you still think that the m in w/mK is milli? [1]

Did you learn all your thermo by reading signs at Home Depot?

John

It's better expressed as w/m-K or even w * m^-1 * k^-1

Better is the wrong word. PROPER is the right word.

Placing it right next to the K makes it a "milli" prefix in ALL circles. So if it is not written right, it will not get read right. It has nothing to do with what someone "thinks".