Steamy streets

[Azalian]

In US TV programs or movies, I often see steam billowing from manholes in the road, (particularly New York)

What is this? You never, (or at least I've never ),seen this anywhere else.

I think it might be some kind of combined heat and power system but that's just a guess.

[Clanad]

In NYC as well as a few other large cities, steam is generated in a central plant and sent by underground pipes to the surrounding area to heat homes and office buildings. In cold weather, the steam, being carried in large, underground pipes (often 20 feet in diameter or more) escapes through the ill fitting manhole covers...
In the case of NYC the company generating the steam also generates electricity so the wires as well as the steam come through the same tunnels. I think the company generating the steam and electricity is Con Edison in NYC...

[Ethel]

The steam coursing under Manhattan is not to be confused with what is popularly called steam rising from many city manholes. The steam in the pipes is invisible, while the so-called steam wafting up from the streets is often vapor produced when underground water hits hot equipment and escapes from beneath the streets. It can also be condensed steam leaking from the Con Ed system.

http://www.gothamgazette.com/article/issueofth eweek/20031110/200/674

[Azalian]

Thanks guys, you've solved a query I've had for ages.