Window insulation reduces

heat transfer Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, ...

from one side of a

window A window is an opening in a wall, door, roof, or vehicle that allows the exchange of light and may also allow the passage of sound and sometimes air. Modern windows are usually glazed or covered in some other transparent or translucent ma ...

to the other. The

U-value The ''R''-value is a measure of how well a two-dimensional barrier, such as a layer of building insulation, insulation, a window or a complete wall or ceiling, resists the thermal conduction, conductive flow of heat, in the context of construct ...

is used to refer to the amount of heat that can pass through a window, called

thermal transmittance Thermal transmittance is the rate of transfer of heat through matter. The thermal transmittance of a material (such as insulation or concrete) or an assembly (such as a wall or window) is expressed as a R-value (insulation)#U-factor.2FU-value, U- ...

, with a lower score being better. The U-factor of a window can often be found on the rating label of the window. Most governments in several countries offer tax breaks or rebate to promote installation of energy savings systems (windows, boilers, insulation, etc.)

U-value

Although the concept of U-value (or U-factor) is universal, U-values can be expressed in different units. In most countries, U-value is expressed in SI units, as

watt The watt (symbol: W) is the unit of Power (physics), power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantification (science), quantify the rate of Work ...

s per square metre-

kelvin The kelvin (symbol: K) is the base unit for temperature in the International System of Units (SI). The Kelvin scale is an absolute temperature scale that starts at the lowest possible temperature (absolute zero), taken to be 0 K. By de ...

: :W/(m²⋅K) In the United States, U-value is expressed as British thermal units (Btu) per hour-square feet-degrees Fahrenheit: :Btu/(h⋅ft²⋅°F) Within this article, U-values are expressed in SI unless otherwise noted. To convert from SI to US customary values, divide by 5.678.

Energy Efficient Technologies

Below is a list of technologies that decrease heat transfer in windows:

Double- and triple-glazed windows

*Clear single glass has a U-factor around 5.7 W/(m²⋅K) or 1 Btu/(h⋅ft²⋅°F) (R-1) *Clear

double glazing Insulating glass (IG) consists of two or more glass window panes separated by a space to reduce heat transfer across a part of the building envelope. A window with insulating glass is commonly known as double glazing or a double-paned window, ...

has a U-factor between 1.8 and 3 W/(m²⋅K) or between 0.3 and 0.5 Btu/(h⋅ft²⋅°F) (about R-2) *Clear

triple glazing Insulating glass (IG) consists of two or more glass window panes separated by a space to reduce heat transfer across a part of the building envelope. A window with insulating glass is commonly known as double glazing or a double-paned window, ...

has a U-factor between 0.5 and 1 W/(m²⋅K) or between 0.1 and 0.2 Btu/(h⋅ft²⋅°F) (about R-3). Double and triple glazing are critical for

energy efficiency Energy efficiency may refer to: * Energy efficiency (physics), the ratio between the useful output and input of an energy conversion process ** Electrical efficiency, useful power output per electrical power consumed ** Mechanical efficiency, a rat ...

. Single glass windows are no longer in general use. The insulation provided by double or triple glazing can be further improved by selecting windows with low-e coatings,

thermal break A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...

s and

argon Argon is a chemical element; it has symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...

or other similar gas between the panes, and also by selecting windows with high energy-efficient frames.

Low-e coatings

Modern double, triple and quadruple-glazed windows have thin, metallic low-e coatings on the panes, which can significantly improve their thermal insulating performance. Another area where low-e coatings are used is

thermal barrier Thermal insulation is the reduction of heat transfer (i.e., the transfer of thermal energy between objects of differing temperature) between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with s ...

s. Some thermal barriers (like Insulbar LEF) decrease thermal losses due to radiation through a low-e folio applied to the

thermal insulation Thermal insulation is the reduction of heat transfer (i.e., the transfer of thermal energy between objects of differing temperature) between objects in thermal contact or in range of radiative influence. Thermal insulation can be achieved with s ...

profile.

Thermal insulation profiles

To reduce heat flow and the U-factor, metal frames should have an insulating plastic profile placed between the inside and outside of the frame and

sash A sash is a large and usually colorful ribbon or band of material worn around the human body, either draping from one shoulder to the opposing hip and back up, or else encircling the waist. The sash around the waist may be worn in daily attire, ...

. These profiles are called thermal breaks and are made from

glass fibre Glass fiber ( or glass fibre) is a material consisting of numerous extremely fine fibers of glass. Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the inventio ...

reinforced polyamide 6,6. The proportion of glass fibre in the profiles is 25%. The material used for this insulating bar stands out for its low

thermal conductivity The thermal conductivity of a material is a measure of its ability to heat conduction, conduct heat. It is commonly denoted by k, \lambda, or \kappa and is measured in W·m−1·K−1. Heat transfer occurs at a lower rate in materials of low ...

value (0.30 W/m2K) and its good mechanical properties even at higher temperatures. A non-thermally-separated frame from an

aluminum Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

window has a thermal transmission coefficient of 6.8 W/m2K. If the system is thermally separated with an insulating profile with a width of 42 mm, the thermal transmission coefficient can be reduced to 1.3 W/m2K. Insulbar LO, a product introduced by Ensinger, is a

lambda Lambda (; uppercase , lowercase ; , ''lám(b)da'') is the eleventh letter of the Greek alphabet, representing the voiced alveolar lateral approximant . In the system of Greek numerals, lambda has a value of 30. Lambda is derived from the Phoen ...

(thermal conductivity) optimized solution for thermal insulation profiles. Its lambda value is only 0.18 W/m2K.

Warm edge spacers

Most modern windows use glazing spacers to keep the distance between their panes for sealing purposes. Many of these spacers are made from aluminum, which is a very conductive material. There is a better alternative for higher insulation performance: special plastic spacers, generally referred to as ' warm-edge spacers'.

Inert gas fills

Double and triple-glazed windows also have

krypton Krypton (from 'the hidden one') is a chemical element; it has symbol (chemistry), symbol Kr and atomic number 36. It is a colorless, odorless noble gas that occurs in trace element, trace amounts in the Earth's atmosphere, atmosphere and is of ...

, or other

inert gases An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. Though inert gases have a variety of applications, they are generally used to prevent u ...

between their panes. It is another key element for a better thermal insulation. Most windows use argon (which is cheaper), but krypton is a better choice of insulation when the distance between the panes has to be smaller (the distance has to be about 13 mm ( inch) for argon, and about 9 mm ( inch) for krypton; increasing or decreasing the space will degrade performance).

Specialized Window frames

The type of window frame and the insulation of its cavity are critical for energy-efficiency and thermal performance (and for strength, durability and maintenance). Aluminum frames are excellent for strength, durability and maintenance but they are a poor choice for thermal insulation. Aluminum is an extremely conductive material. Therefore, thermal insulation profiles are used to create a thermal separation of the inner and outer shells of metal frames. The variety of thermal insulation profiles (Insulbar) allows low U values (for example 1.3 W/m²K by using a 34mm insulation profile and up to 1.1 W/m²K with contemporary aluminum systems) to be reached.

Polyamide A polyamide is a polymer with repeating units linked by amide bonds. Polyamides occur both naturally and artificially. Examples of naturally occurring polyamides are proteins, such as wool and silk. Artificially made polyamides can be made throug ...

insulation profiles with 25% glass fibre content are the best commercially available choice for optimum heat insulation and mechanical properties. Wood frame windows provide better insulation, but they are a poor choice for durability or maintenance (unless you choose wood-clad windows).

Vinyl Vinyl may refer to: Chemistry * Polyvinyl chloride (PVC), a particular vinyl polymer * Vinyl cation, a type of carbocation * Vinyl group, a broad class of organic molecules in chemistry * Vinyl polymer, a group of polymers derived from vinyl ...

and

fiberglass Fiberglass (American English) or fibreglass (English in the Commonwealth of Nations, Commonwealth English) is a common type of fibre-reinforced plastic, fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened i ...

are better insulation and noise reduction materials. Certain windows have vinyl or fiberglass frames that feature chambers, to further enhance insulation and noise reduction.

High insulation-performance windows

Energy-efficient houses in cold climates often feature triple-glazed windows with a U-value between 0.19 and 0.26. In moderate and hot climates, quality double-glazed windows with a U-value of about 0.30 are generally a more cost-competitive and effective choice.

Other ways of improving the insulation of a window

# Using glass with heat reflective properties # Sticking on thermal reflective plastic # Double glazing using heat-shrink plastic film and double sided tape The frame used can also be significant, especially if they are made from a high thermal conductivity material such as metal. In this case, plastic spacers should be used to create thermal breaks between the inner and outer sections of the frame.

References

{{reflist Windows">Insulation Insulation may refer to: Thermal * Thermal insulation, use of materials to reduce rates of heat transfer ** List of insulation materials ** Building insulation, thermal insulation added to buildings for comfort and energy efficiency *** Insulated ...