No matter how good your windows are, they will never equal the level of insulation in the walls of your house. Hi-tech double and triple-pane windows are a huge help, but they still account for much of the heat gain and loss in your home. Depending on their types, number, and locations, upwards of 50% of your home’s energy could be escaping through your windows.
Window coverings can make a big difference in helping to lower your utility bills. This topic can cover both interior (shades, blinds, and draperies) and exterior (awnings, shutters, overhangs, etc.) types. For the sake of simplicity, I’m going to discuss interior window coverings in this post and exterior coverings at a later date (i.e., next week).
As a general rule, window coverings should be mounted as close to the glass as possible and, if mounted inside the window casing, as close to the edges as possible. This will help create a sealed air space around the window. In the summer months, keep window coverings closed during the day to reflect heat away from the interior of your home and open them at night to allow heat to escape and cooler air into the home.
The opposite should be done in the winter. Keep window coverings open during the day to allow sunlight to enter your home, and then close them at night to keep heat from escaping.
Shades are one of the easiest and most effective types of window coverings you can install. There are a number of different types, but they fall into three general categories; roll type, Roman, and pleated or cellular.
Two or three-cell pleated or cellular shades are the ones I like the best. They have honeycombed cells which increase their insulation qualities. They also allow diffused sunlight through them, making them a good option for keeping closed during the day in the summer months. You get the reduced heat gain and still have enough natural light entering the window, so you don’t need to turn on any electric lights.
In the winter months, the pleated cells create dead air spaces, which help insulate your windows. Cellular shades can block upwards of 62% of the heat transfer through your windows. One drawback, however, is that even if they are mounted as close to the glass and edges of the casing as possible, cellular shades are not as effective in controlling air infiltration along their edges as other types of shades.
Roman and roll-type shades are usually heavier than cellular types, plus they sometimes have sealed edges. The heavier material is great for insulation, but they block more natural light. If these types of shades are closed during the day, you will probably need to use electric lights, which will increase your electric usage.
The sealed edges, which are in tracks on the sides of the window casing on these types of shades, allow them to control air infiltration better than other types of shades. Shades without sealed edges will reduce the heat transfer in your home by approximately 28%. Having sealed edges on the shades will reduce the heat transfer by upwards of 45%.
Curtains and Drapes
Because they can be made out of so many different types of materials, quantifying how curtains and drapes perform a bit more difficult. The materials can run anywhere from thin, lacy “gossamer” fabrics to heavy, quilted “blackout” types. Darker colors will absorb heat, while lighter colors will reflect it.
Depending on the time of the year, this may or may not be a good thing. Thin materials will let natural light through but will have almost no insulating qualities. Heavier materials will insulate better but make your rooms as dark as the middle of the night.
The best middle ground for curtains is a medium-weight “closed weave” fabric, a medium-range color, and a reflective white backing facing the window. This will give you the best combination of insulation weight, natural light penetration, and heat reflection. This combination will reduce the summer heat gain in your home by upwards of 33%.
During winter months, curtains will reduce the heat loss from a room by only10%. The reason this is not higher is because of the gaps around the edges of the curtains.
The air between the window and the curtain gets cooled by the outside temperature and then escapes through the gaps along the bottom and sides of the curtain. This cooled air is then replaced by heated air from inside the room, which is drawn through the gap at the top of the curtain. As this cycle continues, the warm air in the room gets drawn to the window, where it is cooled and then drawn back into the room.
There are a few easy ways you can fix this problem. The easiest is to have longer curtains that mount flush with the ceiling and hang all the way to the floor. The sides of the curtains can then be sealed to the wall with Velcro or magnetic tape.
If you don’t want your curtains running from the floor to the ceiling, you can seal the top, along the curtain rod, with a cornice, which will block the airflow. The bottom and side edges can then be sealed with Velcro or magnetic tape. Doing this can improve the effectiveness of your curtains to the point where your heat loss is reduced to 25%.
Whether they are vertical or horizontal, blinds are somewhat of a mixed bag when it comes to their effectiveness in saving energy.
Blinds are great for keeping your home cool during the summer by reducing heat transfer by as much as 45%. In the winter, however, they do very little to prevent heat from escaping from your home. Blinds are not very effective because of their thin materials, plus all the gaps between their slats and around their edges.
Blinds have all the same issues as unsealed curtains, with the added drawbacks associated with their multiple gaps and openings. They do have the advantage of being able to reflect direct sunlight into a room, giving you both a reduced heat transfer (in the summer months) plus diffused natural light.
Overall, however, they are not your best choice of window coverings if you are trying to make your home more efficient.
Probably the biggest factor that enters into most people’s decision on what type of window covering to buy is appearance. I can respect that because, along with liking my home to be comfortable, I also want it to be aesthetically pleasing. If you have your heart set on one type of window covering over another, don’t get too hung up on its potential effect on your energy bills.
Energy efficiency is ultimately the cumulative effect of several things you do to your home. If the window coverings you choose are not as effective in reducing your energy bills as some other types, you can compensate by making adjustments in other areas of your home. After all, it’s your home, and you should be happy with it.