Sun heat through window calculator

How much heat from the sunlight gets through your windows? This calculator aims to give you an idea.

Just provide a few bits of information:

Your latitude:

Window facing direction (from inside):

(Optional) to be more precise, specify how "offset" your window is to the selected cardinal direction. This is an angle, positive number means the window faces more to the right (clock-wise on a map)

Overall angle relative to north:

Date to focus on: (The year doesn't matter)

The solar heat gain coefficient of your window (SHGC): Usually a number between 0.2 and 0.8. This directly multiplies with the sunlight strength. The shape of the charts remains the same. the SHGC only affects the numbers on the left axis.

Area of the window (or fill the HxW below):
Height x Width
If you have multiple windows in the same direction, you can add their area.


Note: The numbers and charts may not be intuitive because there are multiple effects interacting. I might make a blog post to explain them at one point. These are approximations.

(On wide screens, the results show on the right.)

On a clear day on that date, here is how much sun energy is getting inside through the window:

And here is the total energy coming through for each day of the day for the window:

You can click this chart to change the date of the other chart.