Your home’s doors have a large impact on everything having to do with your home: aesthetic appeal, comfort and utility, and even energy efficiency. The cost of keeping the home heated or cooled, for instance, is often affected by which doors you choose to install, and the condition of those doors. In fact, it’s no stretch of the imagination to say that understanding the various characteristics and attributes of different door styles and materials is essential for every homeowner, especially so if energy efficiency is a primary concern.
What is energy efficiency, and how your doors affect it
In the home, energy efficiency specifically refers to the ability to keep your living spaces comfortable with minimal energy and effort. In more concrete terms, if it costs less than average to keep your home heated during the cold months, and similarly cooled during the summer, then your home can be considered energy-efficient.
Energy efficiency is a lot like a car’s gas mileage: the more efficient your home is, the better. Naturally, anything which increases the amount of energy it takes to keep your home heated or cooled will likewise lower your home’s overall energy efficiency. What to expect as a result? Higher gas and electric bills.
With glass sliding doors in particular, there are three ways your energy efficiency can be affected:
Direct conduction refers to the transfer of heat between your home and the outside through the glass or frame of the door. A door that gets hot, for example, would cause your indoor temperatures to go up, too, and would increase your cooling costs in the summer.
Radiant heat refers specifically to the heat component in the sun’s light; the more radiant heat your door lets in, through the glass, the more it costs to keep your home cool in the summer.
Lastly, your door’s ability to keep the home sealed against the elements affects your home’s energy efficiency. If your home is poorly sealed, then it will cost more to keep your home comfortable.
Measuring energy efficiency
You can measure the energy efficiency of your doors in concrete terms. The industry that makes both windows and doors rates the different door properties that make it energy efficient, allowing you to compare different products for relative energy efficiency. At a glance, this is what those ratings mean:
Your door’s U-factor is a measure of the door’s ability to resist transferring heat between your home and the outside; in general, the lower the door’s U-factor, the more energy-efficient it is.
The Solar Heat Gain Coefficient, or SHGC, is the amount of heat from the sun that your door allows into your home; a door with a high SHGC can help offset heating costs in winter, while a door with a low SHGC keeps your home cooler in the summer.
Air leakage refers to how much air a door allows to pass through; there will always be some leakage, but the lower the air leakage, the better the door is at forming a seal between the outside and your home.
Visible transmittance, or VT, is how much light is allowed to pass through your door’s glass; a door with a low VT will keep out sunlight and provide good shading, while a door with a higher VT will help to light up a room.
Lastly, Light-To-Solar Gain is a comparison of SHGC versus VT, and gives you an idea of whether the door is better at keeping out heat, or if it’s better at blocking light.
Glass options for sliding doors
The kind of glass you choose to go with in your sliding doors will affect just how energy-efficient your doors are. Here’s how the most common glass options affect your door:
Insulated glazing refers simply to door glass which uses more than one pane of glass. This is the default for glass doors today, as opposed to the single-pane glass used in older sliding doors. The layer of air in between the panes increases the insulating value of the door.
You can increase the glass’ insulating value with an inert gas fill. By filling the space between the panes with a gas such as argon or krypton, the door will resist heat transfer better.
A low-emissivity coating is a microscopically-thin layer of metal oxide applied to the glass’ surface designed specifically to reduce heat transfer. Low-E coatings give your door glass a better U-factor without affecting its ability to let in light.
Heat-absorbing tints, when applied to your door’s glass, change the color of the glass and help reduce glare while absorbing radiant heat. This gives your door a lower SHGC, and lowers VT as well.
Reflective coatings specifically block more light than heat. They reduce glare and give your door a lower VT, without affecting its ability to block heat transfer.
Spectrally-selective coatings do not affect light transference at all; while the door’s VT is unaffected, they do reduce the door’s SHGC by up to 70%.
Lastly, while not specifically an energy-efficient feature, all of the above can be added to impact-resistant glass. By choosing to add this option, you can make your doors energy-efficient while reinforcing their ability to keep you safe, too.
Christine Salamone is the Creative Director for Renewal by Andersen of Western New York and has over 10 years of experience in the industry. Her expertise at window replacement has allowed her and her team to provide quality service to homeowners in the Rochester and Buffalo areas for many years.