Understanding energy efficiency ratings

We HAD to cut down our increasing energy bills. After a home energy audit, we followed the suggestion of the auditor and decided to replace our windows. After much research and a few recommendations, we decided to buy windows from Champion Window.  Apart from the Energy star label , the windows also had a sticker displaying energy efficiency ratings certified by NFRC( National Fenestration Rating Council). The salesman pointed out that the sticker ensured an energy efficient window.

Curious to know what the numbers and the abbreviations on the sticker meant, I did a quick research and here is what I understood-

There were four performance areas mentioned on the sticker and certified by NFRC. These factors help you choose windows suitable for your local climate.

1.       U Factor measures the rate of heat transfer that is it helps you know how well the window prevents heat from escaping your home. It depends on the insulation, thermal properties of the frame as well as the glazing. U factor ratings fall between 0.20 and 1.20. Lower the rating, more energy efficient is the window, indicating it is better at keeping the heat in. Homes in cooler climates should install windows with lower U factor.

2.       Solar Heat Gain Coefficient (SHGC) measures how well a window blocks heat from the sun from entering the home. Expressed as a factor between 0 and 1, a lower SHGC means the window is better at blocking unwanted heat gain. Homes in warmer climates should have windows with low SHGC ratings.

3.       Condensation Resistance(CR)- Condensation or water build up indicates failure of insulation. The Condensation resistance factor measures how well a window is able to resist condensation. Expressed between 1 and 100, a higher number indicates better resistance to condensation.

4.       Visible Transmittance (VT)- It measures how much visible light comes in through the window.

This is expressed as a factor between 0 and 1 and a higher number indicates more daylight transmitted in.

Next time you shop for windows, look for this certification and be assured that your windows will be  energy efficient and will save money for you by cutting down your energy bills.