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Past Building Science Topics:
Do new windows save you money on your utility bills?
I'm sure you have seen window commercials claiming that they save customers “50% to 60% or even more!!! On energy bills." In return you have not heard them give an actual percentage number on savings in dollars. That is because they have found themselves in some hot water about the claims. In some limited case studies that claim can be true. However in most cases windows are lower on the priority list in an energy upgrade viewpoint for return on investment (ROI). This is not to say that upgrading windows is not a good idea for many reasons, however from a pure energy standpoint and an energy consumption standpoint, it is better to address leakage into the attic space first. Attic air leakage is the primary “driver” for the need to draw in “make up” air, usually felt as a “draft” to the occupants.
Now on the Building Science side of things, with the subject of esthetics aside, we look at the assemblies of systems in the home and can calculate an R-(resistance) Value for that particular assembly. For example an un-insulated 2x4 wall with stucco and drywall still has an R value of Say R 3.5. If you were to fill the stud bays with R-13 insulation, keeping in mind that the wood framing cannot be removed and deducts from the overall assembly R value, the entire wall may now be an R-10 assembly. If you put in a few new windows, you reduce that R-Value again depending on the SF of window area and the R-Value of that window. So now you are down to a R-9 complete wall assembly. If the new window you had installed is an R-3 double pane aluminum window, it may look ugly and not operate well, but if it seals shut and is intact, then the R value is still good.
Continuing from the example above, if you were to upgrade an existing window to say an R-6 window (a good modern window) you have now only increased that specific space's R value. The wall itself it still un-insulated, the new window doesn't effect the overall R value of the entire wall assembly, it only effects the window opening. Lets say after the new R-6 window is installed and the wall interior/exterior is completed, your now back up to a R-10 total wall assembly rating. The cost to achieve that small increase in R-Value does not pencil out in energy savings for several years.
Air sealing the remainder of the home, allowing any air infiltration to occur at windows is a better strategy for a number of reasons; 1. Elimination or reduction of the “stack effect” where air is pulled up into the attic causing drafts from colder areas or crawl space. 2. Allowing for makeup air to be pulled from windows or around doors (if at all) at least knowing that air is clean outdoor air and not from suspect areas, such as dirty attic.
Do new windows save you money?
Window replacement can save money in situations where the old windows no longer close properly or are in seriously bad condition. Otherwise it is a long term investment related directly to looks, value, noise control and others aspects of the home, but not a great investment in pure energy savings and energy efficiency.
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There are a wide variety of incentives and rebates to choose from to help you replace appliances, HVAC systems, hot water heaters and insulation. These incentives and rebates can help you offset the cost of energy efficient products that can help you upgrade your home, save energy and make your home more comfortable. For more detailed information please visit rebates and incentives.
"R" means resistance to heat flow. The higher the R-Value, the greater the insulating power. The amount of insulation you needs depends on the climate you live in. Also, fuel savings from insulation will depend upon the climate, the type and size of your home, the amount of insulation already in your home, your fuel use patterns and family size. All insulation materials are designed at certain thicknesses based on R-Value and application locations. Please note, installing a higher R-Value material into a smaller cavity than what its designed for does not mean that you gain a higher R-Value. It actually lowers it, as the material becomes smashed in the cavity and is less productive.