U-factor


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U-factor

Measure of the heat conducted through a given product or material—the number of British thermal units (Btu) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material. U-factor is the inverse of R-value.

thermal transmittance, U-value

The time rate of heat flow per unit area under steady conditions from the fluid on the warm side of a barrier to the fluid on the cold side, per unit temperature difference between the two fluids.
References in periodicals archive ?
Fully controllable conditions, repeatability, and the ability to reach and maintain steady-state conditions are necessary to determine the SHGC and U-factor of fenestration systems.
Walls and attics are rated with R-value, and windows are rated with U-factor.
An example is the presentation of the provisions for a commercial building wall in terms of an overall U-factor for the opaque portions of the wall or for the entire wall.
Several metrics were proposed for the optical, lighting and thermal performance of TDDs, including: Light Transmittance, Normalized Luminous Intensity, Average and Peak Luminance Indices, Light Diffusion Index, Daylighting Area Coverage, Spacing Ratio, SHGC and U-factor.
R-values, fenestration U-factors, SHGCs, and economizers are now invoked as reference points when demonstrating conformance of the building envelope, insulation, and mechanical and lighting devices to approved drawings.
This means, for instance, that a substance with an R-Value of 12 would have a U-Factor of 0.
For example, a very low U-factor envelope system may not require a perimeter heating system, and very tight, highly insulated homes have been built in Northern Europe that do not require central heating systems.
Pyrolytic Low E coatings have the best combination of solar heat gain and U-factor (measurement of thermal transference) to provide optimum annual energy savings in north-central and northern climate zones.
The new standards also alter the U-factor and Solar Heat Gain Coefficient for the regions (see table below).
The measurement for low heat-loss in glass is called a U-factor; the lower the U-factor the better the insulating value.
3) U-factor: Lower U-factors (inverse of thermal resistance) will more effectively reduce heat loss in climates that require more heating.