# Steam rising from manhole covers in U.S. **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [September 23, 2018, 9:47am UTC](https://boards.straightdope.com/t/steam-rising-from-manhole-covers-in-u-s/821777 "2018-09-23T09:47:54Z")\ **Posts on this page:** 1\ **Showing post:** 3
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [September 24, 2018, 4:17am UTC](https://boards.straightdope.com/t/steam-rising-from-manhole-covers-in-u-s/821777/3 "2018-09-24T04:17:39Z")
Last time we discussed this, [SDMB](https://boards.straightdope.com/sdmb/showthread.php?p=19371656&) Denver claimed to have the oldest continuously operating district steam system in the world, including, last time they looked bits of original insulation made with hollowed-out logs. And NYC said the same kind of thing: > [@Why does steam rise from manholes in Denver?](https://boards.straightdope.com/t/why-does-steam-rise-from-manholes-in-denver/749769/3): > > [We'll be back shortly](http://www.coned.com/steam/kc_faqs.asp) > > _Planting Steam can come from manholes for several different reasons. The most common is water infiltration into the manhole. Water comes in contact with the hot steam main and causes vapor. Another source is leaks, either within the manhole or on buried piping between manholes. There is no “natural” venting process_ Steam also rises from manhole covers where waste-water is released from buildings. In my town you wouldn’t see that, because the sewer system is never vented that way, and is not run in a way that exposes sewer pipes to water infiltration, and it doesn’t get that cold anyway, but I understand that in some US cities traditionally some indigent people sleep over building outfalls in winter. --- _[View the full topic](https://boards.straightdope.com/t/steam-rising-from-manhole-covers-in-u-s/821777)._