A friend was recently complaining about her windows, describing how warm her place had been with this hot summer weather, as well as how noisy, as she lives on a main street, full of loud motorcycles and chatty late night bar go-ers taking advantage of the warm evenings. She asked if replacing her double pane windows with triple pane would help her solve these problems; triple pane is the best, right?
Unfortunately for her, while there are excellent benefits to triple pane windows, it’s not a one size fits all solution for any problem; it’s important to understand window properties and what they do so you can spend your money on the upgrades that will help you solve your specific problem.
Summer Solar Heat Gain:
Triple pane windows are better insulators than their equivalent in double pane. This is because the extra air space created by that third pane increases the window’s resistance to heat flow (increases its insulating R value). However, if we think back to junior high science, we might remember that there are three types of heat flow: conduction, convection, and radiation. R value of the window protects against conductive (frame) and convective (panes) heat flow, slowing the transfer of heat from the hot outside air and sun warmed exterior materials through the window frame materials and the air between the panes of glass and into your home.
The problem is that while the increase in R-value of triple pane will help mitigate a little bit of that heat transfer, that’s not why her family room is so warm (we do not need a high R value to protect a 21 degree interior from a 28 degree exterior, that is only a 7 degree difference and our homes are used to much bigger temperature differences, 30, 40 or even 50 degrees on a cold winter day). The reason her family room is so hot is that the sun is the source of radiating heat flow. R-value is not the solution for this; she needs a physical barrier for the spectrum of waves that is heating her room through radiation (like sitting in the shade, instead of in the sun, on a really hot day).
One of the best options for this is exterior shading. Interior shading (curtains and blinds) will help to smaller degree, but only blocks the sun after it is inside the living space. Exterior shading keeps that radiating heat outside. Good options, depending on the location of the window, the surrounding site, and whether long term options are feasible, can include:
-Trellises or wood overhangs (on its own or with vines or other plants)
-Large window overhangs that block the high summer sun, but let in the lower winter sun, if the window is south facing
-Deciduous Trees (Leaves provide shade in summer but let in the sun during winter)
-Exterior shades/curtains/shutters (permanent or temporary), which are available in lots of different styles
Another option is to install a window with a Low-E coating. This coating lets in light waves but reduces the emissivity of glass – meaning it won’t radiate heat into the room at the same rate as a regular window. This is an option where shading strategies are not desirable and the solar heat gain is considerable, but remember that it also means you are limiting a natural heating source during those winter months as well!
In case I’ve turned you off triple pane, they can be really beneficial! But they benefit us mainly during the winter. The basic equation for heat flow is:
heat flow = (a material’s conductivity) x (the area of this material, i.e. the size of your window) x (the difference in the temperature on the inside vs the outside).
Summer temperatures (or temperate climates) don’t have huge temperature differences from inside to outside. On a 25 degree day, this number would only be 4 or 5 degrees. But on a -30 day, this number balloons to 50 degrees and plays a much bigger role. In our cold climate, the increased insulating values of triple glazing can make a huge impact on your winter energy bills and your home’s environmental footprint; triple pane can be a great investment. Just make sure that when there is a specific problem, invest in the window properties that will help you solve it.
Stay tuned for part 2 – window properties that help you reduce noise!