Thermal Windows save energy

Thermal Windows save energy

Today, we installed into the seaweed cabin thermal windows to save energy. As you recall, I quoted in an Interior Storm Window blog that windows, doors and skylights can lose 35% of energy in a home (Government of Canada, 2020). Initially, we installed some DIY interior storm windows over a year ago. However, when a thermal window supplier offered to install on our island, we decided to upgrade. Although we reduced our electrical bill already by 30% with interior storm windows, we anticipate even greater savings, and improved property value with thermal windows.

The only opening thermal window in the seaweed cabin has a higher U-factor.

The U-Factor

Firstly, manufacturers define the U-factor of their windows as a measurement of the rate of heat loss in Watts per square metre Kelvin (W/m2K). Simply, the lower the U-Value number, the less heat loss of the window. However, the U-factor is only mathematically derived from a formula based on window materials, style and configurations. For example, U-factors rise with windows that open. Nevertheless, in real-world situations, the U-factor could be better or worse than the manufacturer states. Yet, BC Hydro incentive rebates are purely based on manufacturer U-factors. BC Hydro will rebate $50 per window, to a maximum of $1000 for thermal windows with U-Factors 1.40-1.23 W/M2K. For Windows with U-factor <1.22W/M2K, they will reimburse $100 per window or door, to a maximum of $2000 (BC More importantly for us, the U-factor from the single pane original windows, about 5.8 to 5.9 W/m2K, drops to 1.4 W/m2K with double glazed, argon-filled thermal windows. This is a significant improvement from our estimated interior storm windows U-factor of about 4.0 W/m2K (see Table 1)(Stanek windows, 2020).

Table 1 Comparison of U-factor from window types in the Seaweed cabin

Window typeU-factor (W/m2K)
Single pane glass5.8
Single pane glass with interior storm window4.0
Double glaze, argon-filled thermal window1.4
Triple glaze, argon-filled thermal window<1.0

Secondly, as we saw with the interior storm windows, thermal windows will also reduce the potential for condensation by increasing the window surface temperature. Argon gas acts as insulation between the glass, is denser than air, and will prevent currents and drafts from forming when the cold air outside meets the warm air inside. Also, the windows come tightly sealed to ensure this. Furthermore, thermal windows capitalize on low E, emissivity, coatings that basically reflect the interior temperatures back inside without minimizing the amount of light entering the home (see Figure 1).

Figure 1 Argon and Low-E coating helps insulate and reflect the warm interior temperatures thus mitigating condensation on the window
(retrieved from

Although it will take decades to recoup the cost of the thermal windows from heat cost savings, the thermal windows will more importantly appreciate the value of the seaweed cabin as a cost improvement. Figure 2 shows that quality vinyl window replacement can recover about 73.9% of it’s cost at resale (Hanley Wood, 2019); that’s higher than any kitchen or bathroom renovation. Finally, thermal windows can add curb appeal as you can appreciate of our cozy cabin.

Figure 2 Replacement value for thermal windows.
2019 Hanley Wood, LLC. Complete data from the Remodeling 2019 Cost vs. Value Report can be downloaded free at

Looking ahead to the future, a cozier seaweed cabin requires less burning of wood, less green-house gas emissions and better air quality for our community. Thermal windows not only benefit my family, they benefit our community and our planet.