Many window shoppers consider the energy efficiency of many products before deciding to purchase them. Energy efficient windows and doors can make a dramatic impact on energy savings. Let’s look at your options when considering energy efficient windows. Checking a windows U-factor helps in determining energy efficiency.
U-Factor measures the rate of heat transfer and tells you how well the window insulates. U-factor values generally range from 0.25 to 1.25 and are measured in Btu/h. ft² °F. The lower the U-factor, the better the window insulates.
Another important consideration for energy efficiency is SOLAR HEAT GAIN CO-EFFICIENT
The SHGC is the fraction of incident solar radiation admitted through a window, both directly transmitted and absorbed and subsequently released inward. SHGC is expressed as a number between 0 and 1. The lower a window’s solar heat gain coefficient; the less solar heat it transmits. This is really important in the southern part of the US. A good number for this would be .19 or lower.
Many factors come into play when considering a windows energy efficiency.
Glass type and number of panes, typically a 2 pane system filled with argon gas and low-e coatings will meet the needs of folks living in North Carolina.
Materials used in the windows construction will also determine the conductivity of heat or cold transfer into a home. Aluminum or steel windows would conduct the most energy, where as Vinyl windows filled with foam would conduct the less energy.
There are many good window options out there.
This is 50% of the equation!!!
INSTALLATION IS AS IMPORTANT AS WINDOW QUALITY
When we talk about replacement windows in existing wood windows, there are 2 main options to consider:
Pocket replacement vs. Full Frame replacement
Check out my article ”Replacing Double Hung Windows”.
Photo 1 shows a pocket replacement frame inside an existing wood window frame. Note the lack of insulation around the openings, most builders in this area used no or a little fiberglass insulation around the frames prior to 2006.
Fiberglass insulation only works when installed in the batt foam, compressing it around a window is no better than cotton.
Pocket replacement windows do little to help with air infiltration around frames.
Investing large sums of money into some perceived high end pocket window is foolish in my opinion.
If your going to use the pocket method don’t waste a lot of money on the window, it is just a temporary solution at best, and may even be detrimental to the structure of your home if you allow wrapping or capping of existing wood frames.
See the “Replacing Windows in Chapel Hill” article below for more info on that issue.
FULL FRAME REPLACEMENT IS THE BEST CHOICE
Removing the entire window, frame, sills and trim is the only way to insure a tight seal between the window and the existing wall framing, see photo 2 showing low expansion window foam used to seal the new window, this combined with proper flashing will out last any pocket installation by many years and your new windows will make a real difference in energy efficiency.
For the most energy efficient solution, use full frame installation with any high quality window for best results.