Frequently Asked Questions
How does Radiant Barrier (RB) work?
Radiant Barrier is unlike mass
insulation which only slows down or resists heat
transfer. RB reflects heat. Heat always goes cold
by natural law—the problem is how to keep the heat in in the
winter and how to keep it out in the summer. There are
three ways in which heat goes from warm spaces to cold spaces:
CONDUCTION is direct heat flow through a solid object such as
a wall or a ceiling. CONVECTION is heat movement through
air, occurring when air is warmed. The warm expands,
becoming less dense and rising. RADIATION is the
movement of heat rays across air spaces from one warm object
to a cooler object. The heat we feel from a wood stove
or a quartz space heater is radiant heat. ALL OBJECTS
AND BODIES GIVE OFF RADIANT HEAT. Even the insulation in
your attic gives off radiant heat to the cold attic space in
the winter, and to the living space in the summer.
Regular insulation won’t stop radiant heat loss. Radiant
heat must be REFLECTED with a radiant barrier.
What is
the “R” Value of Radiant Barrier?
The “R” value depends
on the number and size of the airspaces surrounding the RB and
on the direction of the heat flow. Since RB is usually
installed on top of existing mass insulation, its R-value is a
moot point. It is RB’s ability to reflect heat that
makes it such an energy saver.
How does RB keep me warmer in the winter?
Just like wrapping a baked
potato in aluminum foil keeps a potato warm longer by holding
the heat in, covering your attic insulation with RB holds heat
in the house. Another analogy would be that RB in the
winter works just like a space blanket, which, although very
thin and lightweight, holds your body heat in. A thin
space blanket can keep you warmer than several heavy blankets.
OKAY, RB keeps heat in in the winter, how can it keep heat out in the
summer?
Just like a space suit, RB
reflects the sun’s heat before it can warm up the insulation
in your attic. When the insulation stays cooler, your
house will stay cooler. It helps to understand how RB
will work for you if you think of other things that work in
much the same way. ASTRONAUTS’ SPACE SUITS—keep body
heat and reflect the sun’s heat away. THERMOS BOTTLES—keep hot things hot and cold things cold. They are
almost perfect insulators. The tight seal and air space
prohibit heat transfer by conduction and convection.
The reflective surfaces inhibit radiation heat transfer.
If the bottle starts out hot, it stays hot because very little
heat is transferred to the cooler outside. If it starts
out cold, it stays cold because very little heat is
transferred from the warmer outside.
What if RB collects dust over a period of time? Will it still
work?
This very issue has been
studied by research institutes. Most attics don't
accumulate enough dust to affect RB's ability to save energy
costs. Thousands of homes and structures have had RB
installed for as long as ten years or more with no significant
accumulation.
Won’t my roof get hotter when I have RB in my attic?
No. RB has been used
extensively in the south, showing no difference in roof
temperatures, as confirmed by field tests.
Do I have to take out my old insulation to put RB in?
No. RB actually makes
your present insulation more effective.
Where do you install RB?
RB can be laid over your
present insulation like a blanket or stapled under your
rafters or crawl space.
What about foil-faced fiberglass? Isn't it just as good as RB?
No. The foil on the
fiberglass is in direct contact with the attic floor.
Aluminum foil becomes more conductive when in contact with a
solid surface. The air space facing the foil surface is
of primary importance.
I already have plenty of insulation in my attic. Do I really need RB?
Regardless of how much insulation you
have in your attic, adding RB will save on your heating and
cooling expense, and keep you much more comfortable. Energy
savings for heating and cooling can vary from 17% to 25%
depending on a number of factors, including climate,
building configuration, materials used, site, family size
and lifestyle. Your RB dealer has been trained to evaluate
your home or business and advise you of your savings
potential.
Has RB been tested by a qualified independent laboratory or
government agency?
The Florida Solar Energy Center
at Cape Canaveral has tested radiant barriers in both small
scale laboratory and full scale building models. Their
results indicate that radiant barriers provide significant
resistance to heat transfer. Current tests conducted by
the Tennessee Valley Authority and the University of
Mississippi support the findings of the Florida Solar Energy
Center. Northeastern Illinois University conducted
winter tests in residential and commercial structures using
infra-red thermograph photography. The photos showed
significant resistance to heat transfer over the regular
insulation.
Will dust collecting on the top of the product hurt its
effectiveness
over a period of time?
A1 “Aluminum
foil exposed in a vertical position since 1929 to the dust and
fumes in the Heat Measurements Laboratory, M.I.T. Samples of
this foil have been removed from time to time and the
emissivity determined. Over a period of 10 years no
appreciable change in emissivity was found.” American
Society of Heating and Air Conditioning Engineers’ Journal
Section, Jan. 1940, Professor Wilkes, M.I.T.
A2 “Thin
layers of dust readily visible to the eye do not cause very
serious lowering in the reflective power. The appearance
of the surface is not a reliable guide as to its reflectivity
for radiant heat, and foil which appears dark or discolored
may have lost little in insulating value if the surface film
is thin.” -The National Bureau of Standards, U.S. Dept.
of Commerce, Letter Circular - 535.
Will the aluminum corrode and lose its effectiveness?
A1 “Hundreds
of samples of aluminum foil have been stored in the laboratory
for various periods of time up to 10 years with no visible
signs of deterioration.” American Society of
Heating & Air Conditioning Engineers’ Journal Section A2
“Aluminum
is highly resistant to the effect of corrosion… Aluminum
is constantly being used where it is exposed to weather, salt
spray and other conditions, which would adversely affect most
metals.” The United States Rubber Co.
Booklet, Serving You Through Science, Page 5.
Do I need a radiant barrier if my home is already well insulated?
A1 SUMMER: “A radiant barrier system can
stop 97 percent of the thermal radiation across an attic
space. If it is not stopped, that radiant energy would
be absorbed by the ceiling insulation and eventually be
transferred to the living space below.” The
Solar Collector, Quarterly Newsletter of the Florida
Solar Energy Center.
“The heat storage capacity
of reflective insulation is low. As a result, it does
not store heat during summer days, only to pass it on down
into the rooms of the house from the attic at night when
coolness is most apt to be desired from the point of view of
sleeping comfort.” Progressive
Architecture, Nov. 1949, Page 76.
A2 WINTER: “CONCLUSIONS: Reflective foil
retrofitted to fiberglass insulated…buildings is
demonstrably effective in reducing heat loss…
Installation of foil in uninsulated buildings would show even
more pronounced reduction in heat loss.” Effects
Of Reflective Foil On Heat Loss in Attic Floors and Metal
Building Installations, Northeastern Illinois
University, Prof. Charles Shabica, May 20, 1986.
If we have failed
to answer your question, please contact us so that we can add
your question to this page.
|
