[Brother]

I replaced a low e window on the east side of my house, and it was the single biggest difference to how my bedroom felt by about 9 am. I used to not be able to sleep in because I would get a sunburn. Moving from 20+ year old aluminum single pane windows made a huge difference.

Did it make my bills go down? Not too much. That with an AC upgrade, switching to all flourescents, and other efficiency projects have dropped my bills from year to year.

Probably the only cost effective project would be to the initial build of a house.