Okay gang...here's one for the books.

The back of my house is sided in vinyl. The remainder of the house is
brick.

The chimney sticks out about 3 feet from the back of the house. There
is a window just to the left of the chimney.

Well, the vinyl on the chimney that is level with the window is
melting.

My first thought was heat leakage from the fireplace.

Well, that's not the case because the area in question is bone cold
with the fireplace running at full bore.

This past weekend I was outside at high noon, EST. It was a bright
and sunny day.

What I saw was the sun reflecting off the window putting a line of
high heat sunlight about 1 inch wide and about 3 feet long...the
length of the melted siding. I could put a fingure on the siding and
hold it there for less than 5 seconds...it was that hot. The window
is somehow acting as a magnifying glass. The other oddity is this
only happens in the winter. I'm guessing due to the seasonal changes
in the position of Sun.

You would have to see it to believe it. Everyone I've talked with has
never heard of this before.

I need to replace the vinyl but I don't know what to do with the
window to prevent damage to the new vinyl.

Any insight is welcome.