HEAT TRANSFER: WHAT DOES IT MEAN?

August 05, 2019

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When you think about insulating your home, you probably think about your walls and roof and the insulation inside them. But when we expand to include other elements of a home’s building envelope, where are the trickier places to manage heat transfer?

If you’ve ever sat next to a poorly-sealed window in the middle of the winter, you know the feeling of that stream of cold air pouring over you. Walls are easy to control heat transfer to: You fill them with insulation and cover up all that unsightly foam and fiber with drywall and paint.

But windows are harder. You can’t stuff the panes with insulation. So what can you do?

How Are Heat Transfer and U-Factor Related?

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Let’s start by talking about what we mean when we refer to heat transfer. Heat transfer can go both ways. It can refer to allowing unwanted cold air into a heated home but also is used when we’re talking about letting hot air and solar energy into an air-conditioned home. Ultimately, the goal is to maintain the indoor temperature without having to waste energy and money on home heating and cooling.

For windows, heat transfer is expressed in something called a U-value or U-factor. U-factor values generally range from 0.25 to 1.25 and are measured in Btu/h·ft². What you really need to know is, the lower the U-factor of a window assembly, the better the window is at managing heat transfer. If you’ve got energy efficiency on your mind when choosing new windows, a low U-factor is a critical choice.

How Do Windows Transfer Heat?

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The most obvious source of heat transfer in windows is through the glass. If you know someone who still has single-pane windows, ask them where the coldest part of their house is in winter or why they steer clear of the sunny spot in front of that window on a really hot day. Without treatment or extra panes, glass is an excellent source of heat transfer.

But a window is more than a piece of glass, and the other components in a window assembly contribute to its heat transfer, too. Air leakage around the frame can contribute to heat loss, especially if a window is designed to open and close. Make sure these sash windows are well sealed when they’re closed to keep your indoor temperature where you want it.

And while many people try to tackle heat transfer in their windows using double glazed or even triple glazed windows, make sure you look at heat transfer from the glazing spacers. Any double or triple-glazed window will have spacers to keep the panes separate. But these spacers, often made of metal, can also be a source of heat transfer, so make sure this is been accounted for in the design and construction of your new windows.

Finally, many windows and doors for high-end homes come with metal frames. Aluminum and steel windows and doors are popular design trends in residential construction these days. But metal is an excellent heat conductor, so without the right frame, you can undo all your hard work managing heat transfer and energy savings through the glazing, spacers and seals.

When you’re selecting energy efficient windows, make sure you understand if the U-factor represents the potential heat loss of the windows panes only or for the entire window assembly. If you’re not sure, ask the supplier or contractor, and confirm that the installation will be in accordance with the manufacturer’s warranty.

Managing Heat Transfer With Thermally Broken Aluminum Windows

Vancouver home with fire-pit.

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For years, wood and vinyl windows have been the standard in residential construction. But wood windows require annual maintenance to protect them from weathering, water damage and pests, and vinyl windows can warp and crack in extreme climates.

Increasingly, homeowners, designers and contractors selecting windows and doors in high-end homes are choosing metal frames. They’re durable and long-lasting, but metals like steel and aluminum are also far more prone to heat transfer than wood and vinyl.

One way to manage heat transfer in aluminum windows is to choose a thermally broken design.

What—broken? Why would anyone pay money for a broken window?

In this case, though, we’re referring to a thermal break, which is an added component or material that “breaks up” the conductive material. In thermally broken aluminum windows, the goal is to insert a break to stop heat loss through the aluminum frame.

In MINIMAL Glass + Door’s thermally broken aluminum windows, the frames are fitted with gaskets and insulating materials that effectively separate the two halves of the frame and disrupt heat transfer. Once the windows are installed, the breaks are completely hidden, so you get the energy efficiency benefit, while still having the clean aesthetic of an aluminum window frame.

And all of MGD’s windows and doors come standard with thermally broken frames, plus triple-pane glazing. So you have an energy efficient frame and glass. Whether you’re looking to manage costs, or want to go the extra mile with an innovative standard like Net Zero, a triple-glazed window with a thermally broken frame will help you see the benefits almost immediately.

For more information and inspiration when it comes to building your next home, visit the MINIMAL Glass + Door website.

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