Should You Choose Low-E Glass Windows?

If you're having new windows installed and have been exploring your options, one that you may come across is low-e glass. This option is particularly common among homeowners who are looking to improve their home' energy efficiency and decrease heating and cooling costs. But what is low-e glass, and is it the right choice for you?

What does "low-e" stand for?

The "e" in "low-e" stands for "emissivity." This is a property of glass that indicates what portion of heat that comes into contact with it is transferred through it. Glass with a high emissivity allows a large percentage of the heat through. Glass with a lower emissivity lets a smaller percentage of the heat through. Standard glass has an emissivity of about 0.84, meaning that 84% of heat is transferred through it. Glass sold as "low-e" glass may have an emissivity as low as 0.02.

What are the benefits of low-e glass windows?

When you outfit your home with low-e glass windows, the warm temperatures outside will have less of an impact on the temperatures inside your home during the summer. This will lead to lower air conditioning bills. In the winter, the lower emissivity of the glass will mean that less heat is passed from the interior of your home to the outdoors -- lowering your heating bill.

If you are trying to meet green building standards, installing low-e glass windows may help, since they will reduce your fuel consumption over all. Either way, this is a good move for the environment and for your pocketbook.

Are there any drawbacks to low-e glass windows?

The only drawback is that they tend to be more expensive than standard glass windows. Expect to add about 10% to the total cost of your windows. If you live in an area with hot summers and cold winters, you may recoup this additional investment in the form of reduced heating and cooling costs. But if you live in a more moderate climate and don't use your heat or air conditioning as often, it may take many years to recoup the additional cost.

Can you reduce the emissivity of existing windows?

Actually, yes. If you've already replaced your windows -- or if the only reason you're considering replacing your windows is because you want to lower their emissivity -- a good alternative is applying low-e films to the existing windows. These films won't reduce the emissivity as much as the low-e coating on low-e glass windows, but it's better than nothing. Low-e films cost less than a dollar per square foot, and they can be stuck to the surface of existing windows. However, this process can be difficult with large or oddly shaped windows -- so you may want to hire a professional to help you with the window installation.