How Heat transference is Measured

It all sounds very technical and how as a home owner are you able to easily compare products and options. A good comparative bench mark is to look at a products R value and U value rating

R- value is the term used to measure and rate  a products resistance to heat loss (a measure of conductivity) . The higher the R value the more energy efficient the product is. This is particularly relevant in rating various insulation products

U – factor Windows are very different from insulation in walls and ceilings. Aluminium windows with double glazing perform a whole variety of functions .. they have to let light in and allow people to see out and they interact with their environment in ways that insulation does not. Windows react to air temperature, sunlight and wind as well as indoor temperatures and occupants use. Windows are also strongly affected  by solar radiation and airflow around them.Therefore the window industry often measures the efficiency of their products in terms of thermal transmission or U factor. U factor is a measure of the rate of heat transfer through a product.
The lower the U Factor the lower the rate of heat loss.

WHATS THE DIFERENCE BETWEEN U FACTOR AND R VALUE?

The biggest difference between U- Value and R- Value is that U-Value measures the rate of heat transfer (or loss) while R-Value measures the resistance to heat loss…. It is a measure of conductivity

A  product with high conductivity will transfer heat quickly , like a hot pan on a stove or a single pane of glass on a cold day. U – Value on the other hand takes into account more than just conductivity. it also is affected by the airflow around the window and the emissivity of the glass.

Emissivity is the ability of a product to absorb certain types of energy (specifically infrared) and radiate that energy through itself and out of a room. A product with high emissivity such as a single pane of glass, will transfer over 84% of the infrared energy from a warm room to the cold outside. This means the lower the conductivity and emissivity of the glass , the lower the rate of heat loss and the lower the U- Factor

Technological advances have seen big advances in low emissivity (low e) coatings on glass which can greatly improve the insulation performance of the glass. Low e glass lets light and heat in , but helps prevent heat from escaping.