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How
Heat is Transferred?
There
are three methods by which heat can be transferred:
- Conduction
- Convection
- Radiation
Numerous
types of insulation and construction materials have been developed
to combat these three methods of heat loss. Standard mass insulation
has been designed to counter the effects of convection and conduction,
but provide no protection against radiant heat loss. Up to 75% of
the heat loss in the home is due to radiation.
Polyair
Insulation products have been designed to minimize radiant heat
loss. The following graphics illustrate the types and percentage
of heat loss.
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Conduction
Conduction
is the transfer of heat through physical contact. Much like the
process of heating a pot of water by placing it on a hot element.
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Radiant Barrier
A
radiant barrier is an obstacle against the movement of radiant heat.
It has a reflective surface that reduces heat loss or gain. Up to
75% of the heat loss in the home is due to radiation. A radiant
barrier is generally not installed with an airspace; therefore,
it has no R-value.
A thermos
illustrates the effectiveness of a radiant barrier. Hot liquids
stay hot because heat within the bottle is reflected back. Cold
liquids stay cool because outside heat is reflected away.
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Convection
The
movement of air can transfer heat from warm surfaces to cooler ones.
As air becomes warm it rises. As the warm air rises and comes into
contact with cooler surfaces it transfers some of its heat energy
to the cooler items it comes in contact with. As this air cools
it falls. This process can establish a continuous current known
as convection. This current is continually cooling down the air
you are heating.
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Radiation
(radiant heat)
Radiation
is the transfer of heat from hot surfaces to cold surfaces through
the air. In the summer, radiation from the sun strikes the outer
surface of your house, causing the surface to heat up.
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Vapor
Barrier
A
vapor barrier retards the movement of moisture into your home and
fiberglass. The movement of water vapor is the prime cause of condensation
problems such as wood rot and drywall damage. It can also reduce
the effectiveness of fiberglass insulation since wet fiberglass
loses its ability to retain heat.
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Radon
Barrier
Radon
is a cancer-causing radioactive gas. It is the second leading cause
of lung cancer deaths in the United Stated.* It is produced by the
decay of uranium-238 present in soil and rock. It easily penetrates
many common materials like gypsum board, concrete block, mortar,
wood paneling and most insulation.
*According
to the American Lung Association
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Reflective
Insulation
Similar
to a radiant barrier, reflective insulation reduces the movement
of radiant heat; additionally, it provides insulating protection.
When installed with an airspace the product can deliver the following
R-values:
Floor R-14.56*
Ceiling R-5.37*
Walls R-6.70*
* Based
on tests using double bubble with ¾" airspace
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