Halve Your Energy Bills by Doubling Up! Part 2

It is not an accident that the list compiled by The National Association of Home Builders on how to save energy in your home has windows included in it. In fact, right near to the top is 'double-pane windows that have high performance glass that helps reduce heat loss in the winter and heat gain in the summer'.

In Part 1 the general case for installing Insulated Glass Units (IGUs) was discussed - in particular noise reduction glass; assuming you are all dying to get on with it, here are the whys and the wherefores of your choices in energy-saving glass.

The most popular reason for installing IGUs is for green and/or energy reasons. In this same vein, the National Association of Home Builders (NAHB) and the U.S. Energy Department recommend that you search out specific qualities when choosing your glass.

Glass can be chosen for its energy saving qualities or for its noise reduction qualities. Since Part 1 of 'Halve Your Energy Bills By Doubling Up dealt with the generalities of IGUs and specifically with noise reduction glass, this Part 2 will only decipher the mysteries of energy-saving glass.

There can be certain options in the qualities of glass that are specifically designed to help with energy reduction and these may be the reasons you might want to change to new windows.

One of these is low-e coated glass. 'Low e' stands for low emissivity; as the word suggests it relates to the amount of heat that is 'emitted' through the glass by radiation. Radiation can go two ways, your heat can radiate out through your single pane windows and the cold can 'radiate' in.

Alternatively, sun shine shining on the window can radiate heat into the room you are trying to cool, and your air conditioning will work twice as hard trying to keep those panes of warming glass cool.

Doesn't sound like much but according to the U.S. Department of Energy either scenario can raise your bill by ten to twenty five per cent. With energy costs on the rise, this represents lots of cash.

So if you choose glass that has low-e coating it will reduce the flow through your window of hot to cold, or cold to hot, and lessen your energy output.

There is another type of glass, mostly recommended for people in mainly hot climates; it is called 'solar control spectrally selective' glass. This blocks the infrared portion of your sunlight.

This is the 'hot' portion that is used to power solar heating panels. Blocking it allows the sun to shine through your 'solar controlled spectrally selective ' pane of glass without heating the room up. Therefore it is not recommended for seasonal climates, where in the cold season we like to feel abit of sun warmth in the home!

Before you think about buying, you would be advised to check out the non-profit organization that spills the beans on doors, windows and skykights. It is called The National Fenestration Rating Council (NFRC) and you can find it on the Internet.

Fenestration, in this case means the design and placement of windows in a building (from the French word for window: fenetre).Windows that are certified by the NFRC carry a label that is invaluable in helping you to make an informed choice. The labels specify four different ratings.

- The U factor measures how well the heat is kept inside a building. For climates which also experience cold weather, NFRC recommend a U factor of 0.35 or below.
- Visible light is also measured - the higher the number the more light is transmitted.
- NRFC also measures a window's ability to block heat from coming in i.e. from sunlight. Zero is the better blocking rate than one.
- Air leakage is a handy one to know about; as heat loss or gain can be from cracks in the construction of the window unit. The Energy Department recommends a loss rating of not more than 0.3 cubic feet per minute.

Another guide is to check and see if the windows you are choosing have the Energy Star label on them; this is approved by the Environmental Protection Agency.

Glass for use in windows is moving into the technological era as fast as anything else, so do not be too quick in choosing 'any old IGUs' - take the time to really get what you want and enjoy the reductions you deserve.