Energy Efficient Windows

Guide to Energy Efficient Windows in Western Washington

As our society becomes more environmentally conscious, more homeowners are installing energy-efficient windows. Using various energy-saving technologies, energy-efficient windows minimize heat gain and loss to regulate a home’s internal temperature and improve its energy efficiency. As a result, homeowners enjoy a more comfortable living space while recouping as much as 30% of their monthly energy costs and increasing their home value.

At Lake Washington Windows and Doors, we only install the best energy-efficient replacement windows on the market. This article will cover energy-efficient windows from top to bottom so you can make the best choice when purchasing your next replacement windows.

What Are Energy-Efficient Windows?

The primary issue with old inefficient windows is that they allow for a significant amount of heat transfer through a process known as window convection. Without going into a detailed science lesson, window convection cools your home’s heated air during the winter and heats your home’s cooled air during summer.

This leads to a massive waste of energy as your home’s HVAC system has to fight against heat transfer by working much harder to keep your home at a comfortable temperature. In fact, heat transfer is responsible for 25-30% of residential heating and cooling energy costs.

Energy Star energy-efficient windows are designed to significantly reduce heat transfer using energy-saving technologies. They address the effects of air leakage, convection currents, and solar radiation by utilizing sealed multi-pane glass filled with argon or krypton gas, low convection frame material, and Low-E glass coating to keep your home at a comfortable temperature while reducing the strain on your home’s HVAC system.

energy efficient window types infographic

The Top 3 Benefits of Energy-Efficient Windows

Choosing energy-efficient windows can provide homeowners with various benefits, including savings and increased home value. The top benefits of energy-saving windows include:

1. Energy Savings = Financial Savings

Homeowners who replace single-pane windows with Energy Star windows can expect to save between $125 to $340 per year in energy costs. On average, homeowners save approximately 12% per year using energy-efficient windows.

Additionally, Seattle homeowners can claim rebates of $50 per window, up to $750, through Puget Sound Energy, as well as a 10% federal tax credit when they replace their old windows with energy-efficient windows.

For typical homes, choose ENERGY STAR and save on average*:

 When replacing single-pane windows you save $101–$583*
and 1,006–6,205* pounds of CO2 per year

Which is equivalent to 51 to 317 gallons of gasoline a year. 

When replacing double-pane, clear glass windows you save $27–$197* and 246–2,001* pounds of CO2

Which is equivalent to 13 to 102 gallons of gasoline

* Ranges are based on the average savings among homes in modeled cities. Actual savings will vary based on local climate conditions, utility rates, and individual home characteristics.


Annual energy savings chart infographic replacing windows in home

2. Increasing Home Value

Energy savings are just one financial benefit that makes energy-efficient windows worth the investment. These new windows will also increase your home’s overall property value and curb appeal as homebuyers are willing to pay a better price for aesthetically pleasing homes with higher levels of energy efficiency. In fact, installing a new set of windows could add as much as $8,500 to $12,000 to your home’s selling price.

3. Improved Home Comfort

Finally, the ProVia Aeris clad-wood vinyl window frames offer an excellent combination of benefits provided by both vinyl and wooden framing materials. These frames are perfect for homeowners who desire the beautiful aesthetic of a natural wood finish while benefiting from the superior energy efficiency vinyl has to offer.

Learn more about our Clad-Wood Window Frames

Technologies Used in Energy-Efficient Windows

As mentioned previously, each component of an energy-efficient window utilizes various energy-saving technologies to reduce the effects of air leakage, convection currents, and solar radiation. Let’s take a look at each of these technologies individually.

Multi-Layer Glass Panes

Some time ago, manufacturers discovered that window insulation could be significantly improved by sandwiching multiple layers of glass together rather than using a single pane. These multi-layer window designs create air pockets between each pane. Those pockets are then sealed to prevent air entering or exiting the space. 

Double-pane windows utilize two panes of glass with a sealed compartment between them. The additional pane significantly reduces the UV rays that can pass through the window, which keeps your home cooler in the summer. Double-pane windows also prevent the warm air in your home from dissipating, which conserves energy during cooler months.

Triple-pane windows utilize a third layer of glass to create two separate sealed compartments. This additional layer of glass can stop up to 95 percent of all unwanted UV rays. Generally, homeowners choose triple-pane windows when enhanced energy performance is their primary objective, as they cost nearly twice as much as double-pane windows. 

Gas-Filled Panes

Manufacturers then discovered that inert gases like Krypton and Argon were much better insulators than air due to their ability to significantly slow the movement of hot and cold air, stopping radiant heat from passing through the window and reducing heat transfer.

With these inert gases serving as additional insulation layers, double-pane windows can provide three layers of protection, while triple-pane windows can provide a total of five protective layers.

Window Frame Materials

While the glass pane makes up roughly 80% of any window unit, installing gas-filled multi-pane glass won’t do much good without an equally efficient window frame. High-quality frame materials like fiberglass and vinyl are far more stable than older frame materials like wood, which expands and contracts allowing air leakage, or aluminum which provides rapid heat conduction.

Fiberglass window frames are by far the most energy-efficient while also the most costly. Alternatively, insulated vinyl frames provide significant energy efficiency with minor expansion and contraction.

Low Emissivity (Low-E) Window Coating

A window’s emissivity refers to its ability to reflect and radiate heat rather than absorb it. Low-E window coatings are microscopically thin layers of transparent metal or metallic oxide placed between the window panes to reflect solar energy.

Low-E coating can increase a window’s energy performance by as much as 40% and can be applied to manipulate heat transfer depending on the surrounding climate by reflecting solar energy away from your home or keeping it from leaving once it has passed through your windows.

Window Spacers

Finally, non-metal and metal hybrid window spacers installed between window panes insulate the pane edges to improve insulation, prevent condensation, and further reduce heat transfer.

Energy-Efficient Window Styles and Frames

At Lake Washington Windows and Doors, we provide energy-efficient options for every window style in our inventory. Some window styles are inherently more efficient than others based on their construction and functionality. Fixed picture windows are intrinsically more efficient than operable ones, while gasketed casement windows are more efficient than single or double-hung ones. The following is a list of all our window styles in order of energy efficiency and frame materials.

Fiberglass Window Frames

fiberglass windows

When it comes to window frames, Milgard’s Ultra Series fiberglass is the most energy-efficient material available today. Due to its extreme durability (a nearly 80-year lifespan) and ability to expand and contract at the same rate as glass, fiberglass window frames reduce air leakage and heat transference more effectively than any other frame material. 

Learn more about our Fiberglass Window Frames

Vinyl Window Frames

After fiberglass come the Milgard Tuscany and Milgard Trinsic vinyl window frames. While vinyl expands and contracts at a higher rate than fiberglass, it’s still a highly efficient, durable, and affordable frame material, perfect for homeowners who value energy efficiency working on a budget.

Learn more about our Vinyl Window Frames

Clad-Wood Vinyl Window Frames

Finally, the ProVia Aeris clad-wood vinyl window frames offer an excellent combination of benefits provided by both vinyl and wooden framing materials. These frames are perfect for homeowners who desire the beautiful aesthetic of a natural wood finish while benefiting from the superior energy efficiency vinyl has to offer. 

Learn more about our Clad-Wood Window Frames

Choose the Best Energy-Efficient Windows in the Industry

Milgard Windows and Doors

Founded in 1953, Milgard is one of the top names when it comes to innovations in the industry. All the Milgard windows adhere to ENERGY STAR® v6 requirements that meet or exceed U-Factor and Solar Heat Gain Coefficient (SHGC) criteria.

And remember the low emissivity coating we talked about earlier? That comes standard in all of Milgards double-glazed windows, known as the Low-E2 Glass. According to Milgard, this coating can reduce UV rays by up to 84 percent.


ProVia has partnered with ENERGY STAR® since 2002 to ensure that they produce energy-efficient, professional-class windows that exceed their certified criteria. Their engineers have worked closely with the voluntary ENERGY STAR program to design and build replacement windows that provide energy savings and value to all customers.

In 2022, ProVia received its 15th Energy Star Partner of the Year Sustained Excellence Award from the US Environmental Protection Agency and the Department of Energy.

Frames For Energy Efficient Windows

The frames of your energy-efficient windows will play a big role in determining their effectiveness. As a general rule of thumb, fiberglass and vinyl offer the best insulation, followed by wood, and finally aluminum and other metal frames. However, aluminum and other metals have poor insulation so it’d be best to stick with fiberglass, vinyl, or composite wood (more durable than normal wood).

Frequently Asked Questions About Energy-Efficient Window

What do energy-efficient windows cost?

In Seattle, double-pane energy-efficient windows in Seattle, including labor, can cost between $400 and $600, while the triple-pane window will be between $500 to $800. Of course, the price will vary by frame materials, the gases used between the panes (if any), low-E coating, etc.

What is R-Value, U-Factor, SHGC, AL, VT, and CR?

Terms such as R-Value and U-Factor are used to describe a windows energy efficiency performance:

R-Value measures thermal resistance or the ability to resist the flow of heat. The higher the R-Value, the more efficient the window is. 

U-Factor measures the thermal transmittance or the amount of heat lost through the material. The lower the U-Factor, the better it insulates.

Solar Heat Gain Coefficient (SHGC) represents the amount of solar heat that passes through the glass.

Visible Transmittance (VT) represents the amount of daylight (or visible light) that passes through the glass. A high number allows more light to pass through the glass than a low number.

Air Leakage (AL) measures airflow via the window joints. A lower AL means less air leakage.

Condensation Resistance (CR) measures a window’s resistance to condensation. The higher the CR, the more resistant.

How do I tell if it’s time to upgrade to energy-efficient windows?

You’ll know it’s time to upgrade if your energy bill is increasing, you can feel a draft throughout your house, your windows are hot or cold to the touch, or they are showing visible signs of aging.