The specific phrase, “windows of Heaven”, is mentioned in three books of the Bible. In Genesis, 2 Kings, and Malachi.
The sequence goes something like this. In Genesis God opened the windows. In 2 Kings, the skeptic doubted both their existence, and God’s provision. In Malachi, God promised that if we would bring all the Tithes and Offering into the storehouse, He would pour out overwhelming blessings from the windows.
In the first two books, the skeptic’s doubt cost them their lives, even while Noah and Elisha were spared. In the third book, He lets us choose which group we will be in. I choose to believe the Creator of those windows rather than outsiders. After all, they are “all season” windows, God can bless in a season of trial as easily as He can in a season of blessing!