On Tue, 20 Sep 2005 12:40:27 GMT, "Alan Raisanen"
wrote:

Hi Group.
I have a 30 x 40 foot metal polebarn which I use for a shop. The back
third, about 30x15, has been internally partitioned and fiberglass
insulated, and I heat it with forced air from a wood boiler and heat
exchanger. It stays quite cozy in the winter (upstate NY), and I use it as
my machine shop. Welding and storage occur in the unheated portion. I would
like to add some insulation to the front portion so I can keep a little heat
on in there. Has anyone got any experience with the radiant barrier types of
insulation systems? I am seeing rolls of the aluminum-foam-aluminum
insulation being quoted with a 14.5 R value. For example, see
http://www.insulation4less.com/
This stuff looks easy to install, being only 1/4 inch thick or so, but does
it really work or are they being optimistic about the numbers? I could go
with a conventional fiberglass system too, it will just be more work to
install it.

Al

I'd test a sample of that foil/foam stuff before I bought much of
it. I'm very skeptical of their R value rating.

They may support those ratings by testing with radiant heaters that
heat objects in the space while air temp stays relatively low. I
strongly doubt that it has R value of 14.5 in terms of thermal
resistivity.

How to test: insulate a small enclosure with the stuff. Tape the
corners and seams to eliminate leaks. Put an electric heating
element, as perhaps a hair dryer element or even just a power
resistor, inside the box, along with a thermometer or thermocouple
probe. Shield the thermometer or probe from radiant heat with a piece
of metal tubing open on both ends.

Feed a measured small amount of power to the heater -- maybe 5 watts.
An approximate but very simple test could be done with a 5-watt
nightlight as a heater, if the thermometer is well-shielded from
radiant heat from the bulb while being open to the air inside the box.

Run it for long enough to reach equilibrium temperature -- might be
several hours. Equilibrium is when the temp inside the box stops
rising.

The R value will be

R = dt * area * 0.293/power where dt is the temperature rise inside
the box above ambient area is the total area of the box's surface and
power is the power (in watts) fed to the heater. Amps * volts.

If the box was 1 foot on each side (6 square feet total) and the
heater was fed 5 watts, dt would be 41 deg F if R is really 14.5.

I've not included the R value of the cardboard here so the rating will
be a bit generous.