Do you have questions about best practices for your home’s energy conservation? Do you need solutions to your heat loss problem? Worried if your home meets new requirements? Wondering how can you improve heating efficiency, especially if you live in a colder climate?
Shawna Henderson responds to contractor advice and gives you better solutions that guide you in the right direction.
HOMEOWNER: Do I want Low-E windows in Nova Scotia on the south-facing side? I like heat and light. The house doesn’t need cooling in summer. But keeping heat in in the winter is always nice. I can’t tell if the argon is the main thing for keeping it in, or if Low-E helps. And how much does it darken the window?
SHAWNA HENDERSON: Both. Low-E ‘bounces’ the heat back into the house and argon slows the connective loop between the panes of glass. Neither will impact the amount of light that comes into the house in a way that you can sense. Go for 3 panes and one with the highest center of glass R-value ( or lowest u factor). This will give you far more comfort in the cold months because you will be radiating less heat to the cooler surface of the glass. You can get far more precise than this quick note about the various factors that make a good window, but unless you’re trying to hit an energy use target, all the info you need is: 3-pane, Low-E, argon, with the highest R or lowest U.
Also, specify insulating spacers between the panes - that is one of the things that improves the R-value/ U-factor of the window, along with Low-E and argon and the 3rd pane, so going for the best you can find gets you all the high-performance features.
CONTRACTOR: Low E is a coating on the glass to reduce UV and infrared, but not visible light. It protects furniture and floors etc. It doesn’t have anything to do with heat except it might reduce infrared light and passive heating, without sacrificing brightness.
SH: It’s true that Low-E reduces UV and protects furniture and floors. However, ‘Low-E’ stands for low-emissivity, which means it slows the transfer of energy, which, for our purposes, translates into slowing the transfer of heat. Low-E re-radiates energy into the house, reducing heat loss in heating climates or 'bounces' the sun's energy off the window before it gets into the house to reduce heat gain in cooling climates (which way energy is ‘bounced’ is dependent on which surface of the glass is coated).
CONTRACTOR: Typical new wall construction is R20 or so, as a minimum. Old houses might be R14. As a comparison to the wall, windows are typically R3-5 and can be R10 for the best 3-4 pane windows in the world. So, they’re already the weakest link in a home (assuming it’s otherwise airtight etc). The thermal break between two or more panes is doing the bulk of the insulation... the coatings contribution is very minor. So, don’t stress about the decision too much. Get triple pane if you’re really motivated around winter warmth and don’t bother with the coatings.
SH: This is not how window technology works - it’s not one or the other. The best performing windows use a system of coatings, inert gas fills, insulating spacers. A triple pane without coatings and gas fills will not perform as well as one with.
Please go for low-e, argon, insulating spacers, regardless if you choose double or triple pane. The cost is negligible, and many suppliers here in Nova Scotia don't sell anything without a Low-E coating. You will not see a difference in light, and you will have a much-better performing window that improves the comfort level of the space by increasing the temperature of the interior surface of the glass, meaning you're not radiating as much heat to the cooler surface.
After many years of research and improvements in window tech, the benefits of Low-E are not disputed. The problem sits with how we measure the 'effectiveness' of heat transfer with a static metric like R or U - we don't have a metric for improved comfort that translates as readily to a quantifiable "dollars saved vs. BTUs travelling through glass at a certain rate". High-performance windows are always going to look like a lost investment because of this. Windows are a 'permanent' part of the house - a generation investment - and shouldn't be judged on a short-term payback.
HOMEOWNER: I'm confused because the people selling it are more focused on cooling in the summer, and I'm way more interested in heating in the winter.
SH: We're seeing lots of high performance houses with large S/SW/W facing windows, cooling is an issue because of design choices around window sizing and orientation. Are you looking at US sites or are you looking at Canadian sites for your information? US is much more focused on cooling than Canada.
Also, if you're replacing a window on anything other than a net zero/passive house/high performance project in most of Canada, improving heating & comfort levels is going to be your #1 concern.