Found on family Handyman web site.

[WorthFlorida]

 

[Fitter30]

At least its not white or brown.

 

[Sponsor]

 

[Breplum]

When you just need a little warmth, like in Florida...
Or: Home-made high velocity ducting

 

[WorthFlorida]

When you just need a little warmth, like in Florida...
Or: Home-made high velocity ducting

Some comments on Handyman is that it is for humidification with rain water.

 

[WorthFlorida]

At least it's not white or brown.

It must be old. I do not remember the last time I've seen galvanized downspouts? I think is was usually used on commercial buildings.