Put your glass under the lamp.
Pick what you have and what you are considering, set your winters and window area and watch heat arrows, glass temperatures and a rough heating-cost difference change.
- Pick your glass
- Watch the arrows
- Free, no signup
Compare the glass
- Inside glass at 0 F, now0 F
- Inside glass at 0 F, new0 F
How this works
- Heat loss through glass is about U-factor times area times the degree-days of winter, so a lower U-factor and a colder climate change the answer in proportion. We use typical whole-window U-factors: about 1.0 for single-pane, 0.5 for double-pane, 0.30 for double low-E with argon and 0.20 for triple low-E.
- Cost converts the heat to therms and divides by a furnace efficiency of 80 percent. It covers heating only and only the windows, and your real bills depend on the whole house, the weather and your habits.
- The inside glass temperature shows why cold windows feel drafty and collect condensation: at 0 F outside and 70 F inside, single-pane glass is close to freezing while good glass stays much warmer.
Saved. Your answers will travel with the estimate form at the bottom of the page.
Four things set the heat loss.
U-factor
A lower number means less heat gets through.
Window area
More glass means more heat to hold in.
Climate
Colder winters multiply every difference.
Installation
Gaps around the frame can undo good glass.
Glass Lab questions
Will new windows really lower my energy bills?
They can, especially over old single-pane or leaky windows, but savings depend on your house, climate and habits. Our Glass Lab gives a rough, honest comparison, and we do not promise specific savings.
What glass should I choose?
It depends on your climate and which way each wall faces. Low-E glass helps almost everywhere, triple-pane shines in cold climates and low solar heat gain glass helps hot, sunny walls. Our Sun Dial shows what each wall needs.
How long does installation take?
Many homes take a day or two for a handful of windows and a few days for a whole house, plus the lead time for made-to-order units. Our Window Counter estimates the days for your house.
Want a real estimate?
We recommend a glass package for your house and put it in writing.