Question: What's with all the steam rising in downtown Duluth?

Today’s question comes from the News Tribune newsroom, and it refers to the steam that can be seen escaping from various vents downtown during the city’s colder months.

If you’ve lived in Duluth for a while, you probably know that the city has a steam system that has heated much of downtown since 1932, when the technology was state of the art. Newer residents and visitors, however, might find themselves wondering about the curious vapor.

It’s a sight that likely won’t last, however.

Changes are afoot as the city is in the midst of a $40 million switchover to a closed-loop hot water system during the ongoing Superior Street construction project. Leaky, old steam pipes are being replaced with modern, insulated lines to more efficiently deliver heat to customers.

The hot water system is more energy-efficient because water temperatures can be lowered and less water is used.

Here’s how steam heat works in Duluth, according to Duluth Energy Systems, which operates the city’s system:

  • At the Duluth Steam Plant in Canal Park, 90 million gallons of frigid water from Lake Superior are heated in a coal-fired boiler to 360 degrees to create high-pressure steam.

  • That steam is distributed to more than 160 buildings downtown through a series of underground pipes, most of which are also 85 years old or more.

  • The steam is circulated throughout the buildings to heat office spaces and living areas.

  • As the buildings use the steam, the vapor cools and condenses back into water at a temperature of about 180 degrees.

  • The steam is then discarded into storm or sanitary sewers.

The new closed-loop hot water system — already in use in Canal Park — is more efficient than the open-loop steam system.

For starters, it operates at a much lower temperature than the existing system. Any heat that’s not used by a building is transferred back to the steam plant to be reheated and pumped back into the loop, which saves water. The water being reused is also much warmer than the lake water, so less energy is needed to heat the water back to operating temperature, which saves energy.

Here’s how the new hot water system works, according to Duluth Energy Systems:

  • Boilers at the Duluth Steam Plant produce steam by combusting gas or coal, with future potential for biofuel use.

  • Hot water is created by transferring the steam energy to the closed-loop hot water system.

  • The hot water is distributed to buildings through a system of underground pipes.

  • When the water reaches each building, it transfers heat to that building’s separate hot water system through an energy transfer system in the building.

  • The water is then returned back to the plant to replenish the heat that was transferred to the building.

  • The system operates continuously.

Steam won’t disappear from the scene completely, as Essentia Health and St. Luke’s medical facilities rely on steam to sanitize medical tools and equipment.

But the days of standing next to a vent downtown on a frozen day and getting a nice, warm steam hug are numbered.

My favorite spot has always been the vent on the backside of the CenturyLink building, in the alley above Superior Street at Fourth Avenue West. I often pass by it on my way to grab a mid-afternoon coffee.

Next time you're on a subzero stroll downtown, stop by and spend a cozy moment or two — while you still can.

What do you wonder? Have a quirky question? Anything local goes! Get in touch at or on Twitter @NorthlandiaDNT.