Windows are usually the “path of least resistance” when it comes to heat loss/gain. Because you’re cutting a big hole in your building, it’s not hard to see where your heat loss is likely to come from. So compromising on window quality could cost you more in heating and cooling bills than you will be saving on your window purchase.
Our windows are of medium quality and, while only four years old, I noticed the other day that they are already beginning to warp. Good windows don’t warp. Good windows open and close easily despite the temperature outside and inside. Good windows frames don’t deteriorate after only four years. Conclusion: Our windows suck. (Note: these windows were installed when we bought the house. When I asked the builder which company the windows were from, I learned it was a reputable local manufacturer, but the builder chose sub-quality windows….to save money. Big surprise.)
So, IF you have to replace your windows — and really think about that, because a lot of older wood windows with storm windows don’t necessarily need to be replaced, just restored — as with anything, buy the best you can afford, with maximum energy efficiency. Energy resistance here is measured as “U” value which is the inverse of “R” value and therefore you strive for a lower number (clear as mud, right?).
There are at least five things to consider when choosing energy efficient windows.
- Single, double or triple paned (glazing). Unless you are building in a climate that is 20C 365 days of the year day and night, you should consider buying double-paned windows. They protect against the weather significantly better than single-paned glass. Whether or not to go the step further and invest in triple paned depends on many factors. They are usually significantly more expensive and the additional weight needs to be taken into account when adding to an existing building or new build. [note – if you live in a designated historical house, you may be restricted by what you can do. Check local by-laws to see what is permitted.]
- The spacers between the glass panes and the frame. The seal can wear over time due to exposure to direct sun and extreme temperature swings. Ask what the spacers are made of. Metal spacers can hasten the seal breakage as they can expand and contract quickly in direct sunlight.
- The insulation used in the window frame itself, and between glazings (glass panes). What type of gas (if any) is being used between the double or triple-paned glass? Usually argon or krypton are the gases of choice and offer the best protection against air-flow.
- The installation process and insulation added around the window frame. Above all else, if the windows aren’t installed properly with sufficient insulation wrapped around the frame, they won’t be as effective as they are intended to be. Make sure the installers know what they are doing and fill and seal any gaps that are left after the windows have been installed and before the rest of the framing is put in place.
- High-quality frame: Glass expands and contracts at one rate and wood, aluminum and vinyl all expand at different rates. It means that the seal between the glass and window, if not well-made, will separate and the seal can break. A fiberglass frame provides one of the best framing materials because the material expands and contracts at the same rate. Aluminum frame is one of the worst frames because aluminum is a conductor of heat/cold.
- Adding a low emissivity coating, and argon gas to the windows for more effective resistance to heat loss/gain. Note, that in cooler climates the low e coating should be applied on the interior side, and in warm climates on the exterior glazing.)Glass expands and contracts at one rate and wood, aluminum and vinyl all expand at different rates. It means that the seal between the glass and window, if not well-made, will separate and the seal can break. A fiberglass frame provides one of the best framing materials because the material expands and contracts at the same rate.