One of the most important glass performance measures is U-value—also known as U-factor—which measures the insulating characteristics of the glass, or how much heat flow or heat loss occurs through the glass due to the difference between indoor and outdoor temperatures.
What does U in U-value mean?
Thermal transmittance, also known as U-value, is the rate of transfer of heat through a structure (which can be a single material or a composite), divided by the difference in temperature across that structure. The units of measurement are W/m²K. The better-insulated a structure is, the lower the U-value will be.
What is the difference between U-factor and R-value?
R-Value is a measure of thermal resistance, or the ability of an object or material to resist the flow of heat. U-Value is a thermal transmittance, or the heat loss through a structural element.
What is meant by U-factor?
U-factor is the rate at which a window, door, or skylight transmits non-solar heat flow. For windows, skylights, and glass doors, a U-factor may refer to just the glass or glazing alone.
Is .27 a good U-factor for windows?
In a cold climate a good U-factor for a window is between 0.17 and 0.39. (That’s between R-6 and R-2.5). Lower is better with U-factor–the opposite of R-value, when higher is better.
Is higher or lower U value better?
U-values can tell you how well an insulated glass unit (IGU) will hold in heated or cooled air. The lower the number, the better the insulating performance. U-values generally range from 0.1 (very little heat loss) to 1.0 (high heat loss).
What is the best U value insulation?
Obviously, the insulation material will improve the U value. The best currently available is the Val-U-Therm system (available from Scotframe) with a U value of 0.09W/m2K from a wall thickness of 235mm, plus the outer skin.
How do you convert U-factor to R-value?
Calculate the U-factor by using this formula: U-factor = 1/Sum of the R-values. Using the previous example with an R-value of 16, the U-factor is one-sixteenth, or 0.0625.
Is thermal conductivity the same as U value?
U-value = Thermal conductivity / thickness (where the thickness is measured in metres). When you are comparing U-values, a lower number is better – i.e. a lower U-value signifies less heat loss through a material; therefore it is a better insulator.
What is the U value of steel?
0.12
For example, a building with material with an “R” Value of R-11 converts to an “U” Value of 0.09 ( 1/R or 1/11 = 0.09). The following is a table of common materials and their corresponding “U” Value.
U-Values for common materials.
| Cold Mass Specific Gravity | |
|---|---|
| Material | Specific Gravity |
| Steel | 0.12 |
| Aluminum | 0.23 |
| Copper | 0.09 |
What is the best U-value for double glazing?
1.2 W/(m²K)
Modern double glazed units use Low Emissivity Glass (Low-E) and argon or krypton gas in the cavity and the best double glazed windows can achieve a U-value in the region of 1.2 W/(m²K).
What is the best U-factor for windows?
For most energy-efficient windows, the U-factor for the entire window assembly is higher than the U-factor at the center of the glass. The best, high-performance, double-pane windows may have a U-factor of 0.30 or lower, indicating that they are very energy-efficient.
Which windows have the best U-value?
Put simply, double- and triple-glazing have become the standard of energy-efficient windows. Moreover, the Efficient Windows Collaborative says glazing makes for better insulation performance: double-pane windows can have U-values of 0.3 or even lower, while some triple-pane windows can be as low as 0.15.
How do you reduce U-value?
By adding insulation to the walls of your home, you reduce the U-value and in turn you will save money on your heating energy bills.
What is the importance of U-value?
Materials with lower U-values are better insulators. So, the lower the U-value, the less heat will be lost from your home. Although windows with low U-values may be more expensive, they will give you better energy efficiency and help you save more money on heating bills – giving you long-term savings.
Is 1.4 U-value good?
A period property with little or no wall insulation is likely to leak more energy than a property built in the last 10 years, therefore, a U-value of 1.4 or 1.2 will be appropriate as the overall heat loss from the property can only be countered so far with energy efficient windows.
What is the U-value of 100mm Fibreglass?
2.2 m2K/W
100mm of glass fibre insulation batt would have has an R value of 2.2 m2K/W – which makes the wood fibre more resistant to heat loss.
What U-value does 50mm Celotex?
Technical Spec
| Product Code | Board dimensions (width) x (length) = (m²) | U-value (W/m²K) |
|---|---|---|
| Celotex CW4040 | 12×0.45×1.2 = 6.48m² | 0.56 |
| Celotex CW4045 | 11×0.45×1.2 = 5.94m² | 0.50 |
| Celotex CW4050 | 10×0.45×1.2 = 5.4m² | 0.44 |
| Celotex CW4060 | 8×0.45×1.2 = 4.32m² | 0.37 |
What is the U-value of 100mm Celotex?
0.2 W/m2k .
Using Celotex to fill the cavities is more expensive, but you will only need to use 100mm celotex to achieve a U-value of 0.2 W/m2k . The only thing to bear in mind here is that you still need to keep a residual cavity on the outside – but this means the cavity can be marginally thinner.
What is the U value of a window?
The typical U-Values on windows is a measurement of heat loss and the rate at which it is lost. U-Values indicate the overall performance in retaining heat and preventing it from escaping to the outside. U-Values are measure in Watts per square metre Kelvin, or W/m2 K.
What does R-value indicate in insulation?
The term “R”-value represents how well insulation restricts heat flow. To test for R-value, a piece of insulation placed between two plates in a laboratory. Heat is then passed through the material to test the thermal conductivity, measured in BTUs per hour. The greater the “R”-value the better the insulation.
