Depending on the condition, size and location of your windows, they can have a drastic effect, both positively and negatively, on the energy consumption of your home. As we examined earlier this week on the Green Blog, the location of the windows in your home, in relation to the seasonal rising and setting of the sun, are a key factor affecting energy usage.
A home will absorb more ambient energy through a window, even insulated, than through a wall, as the natural transparency of the portal will allow light to pass through the envelope, heating the floor and interior of a building. If your home is constructed to passivehaus standards, often this will be taken into account as part of the heating structure of the building, contained by superinsulation. In certain climates, however, it makes sense to shade your windows, either with an overhang, tree, or commercially available film, in order to mitigate the amount of sunlight allowed into a building.
In colder climates, older windows can be a major source of heat loss, potentially compromising the building's envelope in the opposite way. When addressing issues with older windows, it often becomes hard to decide whether they should be repaired, augmented, or simply replaced outright.
Each of these strategies have their own cost structures and benefits. Installing new windows, for instance, will certainly make your energy bills drop, although you may find yourself disappointed by how little, depending on whether or not your windows are a main source of energy loss (which may not always be occurring where you think). According to Michael Blasnik, a Boston-based energy consultant who spoke at the Building Energy 12 conference, homeowners should only expect a 1-4% drop in energy consumption with new windows.
"Window replacement has a 200 to 300 year payback period," Blasnik asserted. "A Wisconsin study found that a lot of the expected energy saving is lost by the reduction of solar gain. Most replacement windows have low-solar-gain glazing, so maybe half the energy saving is gone due to the reduction in solar gain. I tell people, go ahead and replace your windows if you want, but don’t expect significant energy savings."
If your home has smoothly functioning storm windows, you may not have to do anything at all, as the energy performance of single-glazed windows with storms can be surprisingly close to that of newer, double-paned glass. The annual difference in energy consumption may amount to only a few dollars per window, defeating the economic incentive for altering them significantly.
If you're not quite ready or able to install all-new windows but want to tighten up your home for winter, there are a variety of options available to you. Checking the weatherstripping of your windows, and even adding another layer of it for Winter, is absolutely crucial. Over time, these strips can wear to a surprising degree, leaving you with a draft that may completely escape your notice.
Specifically constructed window inserts, like those manufactured by Indow and available at Green Conscience, are another option, one that is especially fitting for single-paned windows that don't have storms. Custom sized, they lock in place with an airtight weatherstripping seal, adding a secondary layer of insulation to your windows during seasons of more extreme weather, cold or warm. In addition to adding a layer of acoustic insulation, these inserts can also be manufactured to restrict the amount of sunlight allowed through, helping to maintain an ambient cool in the Summer.
When approaching your windows from an energy efficiency standpoint, there are often no easy, clear-cut decisions to be made. Each home and situation is different, and whatever decision you make will be driven by climate, budget, and a host of other factors, yet as a homeowner, this is one arena where you have no lack of options.