This article actually never answers the question, why does this steam network releases steam in the streets?
https://web.archive.org/web/20160811170408/http://www.coned....
This can be a large portion, e.g. in older systems from the days when fuel was cheap, and pollution wasn't a topic.
Modern systems attempt to recover exhaust heat, and can be 90-ish% efficient.
There's a more obvious argument that leaking steam into the streets is a waste of heat, but that still depends on your goals. You might like having warmer streets.
You're thinking of forced hot air systems, but these do not vent combustion exhaust into living space. There are fuel remnants and combustion byproducts in the exhaust which would smell bad, and kill people.
Combustion exhaust, and all of the heat it contains, goes up the chimney and is lost. The living space air is heated by proximity to the combustion chamber, but circulates in a separate closed loop.
Also, in a forced hot water system, there is no air circulation at all. 100% of the air involved is heated and goes straight up the chimney.
Aside: Some people call FHW systems "boilers" instead of "furnaces", but this seems to vary by region. Where I'm from, "boilers" are steam systems only -- which seems reasonable, since water is not boiled in a FHW system.
> Also, in a forced hot water system, there is no air circulation at all. 100% of the air involved is heated and goes straight up the chimney.
Without disputing your other points, this isn't right. I'm not thinking of any particular style of system. The point of every heating system is to release heat into the air. The problem people experience is that the air they occupy is too cold, and the solution is to heat that air. The point of a system that circulates hot water through your building, or your apartment, or anywhere, is that the hot water will release heat into the air there. Heating the air is the only goal regardless of whether the system involves circulating any air.
The point that you can lose heat by venting hot combustion waste to the external atmosphere is well taken.
So when I said that 100% of the air involved in a forced hot water system is used for combustion and exhausted, I mean the air at the furnace, not the air that is indirectly heated in the living space.
Agreed that the goal is to heat the living space though, including the air. A forced hot air system does that directly (pushing heated air into living space), and forced hot water does so indirectly (pushing hot water into radiators in living space, which heat the air by convection).
Radiant floor heat is another example where there's no air at the heat source.
This kind of argument works for power stations, but it doesn't work for heat because it's obviously not more efficient to heat 13 miles of piping in addition to your building rather than just burning stuff in your building.
The rest (almost 30%) goes up the chimney, or radiates out from the furnace itself. It's heat, thermodynamically speaking, but it is not useful heat.
(Some is also lost to light energy, and some fuel is not fully-combusted. These account for a small but measurable loss.)
How is it more economical to have enough leaks that people start talking about it instead of doing proper maintenance? Especially since this situation seems fairly unique, I've never seen this outside the US, and could only name San Francisco and New York as places where this happens. So what discourages maintenance in those places compared to everywhere else?
Doing proper maintenance requires opening the streets, which is expensive and causes confusion and delay, so there's some amount of acceptable leak before it's a good idea to fix it. There's always a chance of finding unmapped critical infrastructure when you dig, which adds more risk. Plus, when you fix it, you lose the street cred.
This reminds me that in Paris you can pretty often see water flowing on the street, it seems that the Paris water supply has a tendency to leak that I just don't see in other towns (but then, i am really walking for kilometers through the city when visiting paris so maybe I just have more opportunities to spot leaks).
https://parisianfields.com/2012/03/11/a-most-unusual-water-s...
My natural gas supplier for example (which is used primarily for heating where I live) routinely raises prices and always flouts state law. My only option would be to discontinue use of natural gas, which would cost me even more money.
I’d think there would be some sort of safety system for venting pressure. Or even condensation around the hot pipes (which seems to be why the same thing happens in New York which also has a steam network)
All of the above could work too.