[stealthn]

I am convinced our windows in our house are toast. We build the house in 2001 and have had the calking redone on schedule, but I’m sure the thermal value of the double pane has given up. It’s been cold here in winter and the house has been way colder this year.
My wife gave me a thermal gun for my birthday, so I measured the walls at 20 degrees C and the window right next to it at 10. We have a lot of windows and two rooms with two story windows.

Is there any tools or anything to measure the thermal efficiency of the glass?

I am dreading the cost and hassle of replacing all the windows.

Thoughts?