A few years ago, we picked up an account at an apartment complex that consists of eight buildings. The mechanical room is in a separate building that houses a low-pressure steam boiler, the DHW system, a condensate station and a boiler feed system. We were called in to try to improve a poorly functioning two-pipe steam system. The buildings were built in 1953.

On our first site visit, we noticed the burner cycled often, yet the steam struggled to reach the areas furthest from the boiler room. Along with many other changes, we were able to reduce the size of the flame and increase the length of the firing cycle. This helped with heating the furthest heat emitters (recessed convectors).

Then, one of the feed pumps on the boiler feed station failed. The maintenance director informed us that these pumps typically last one heating season. He then pointed to a pile of pumps that had failed. We replaced the pump and noticed the three-year-old boiler feed tank looked about 20 years old from the inside. Later that season, one of the pumps on the condensate station failed, and the tank was loaded with rust inside.

There is an underground concrete vault that connects the mechanical room to the other buildings in the complex. The chase is approximately 2 feet wide by 2 feet high, and about 45 feet long. The base of the chase is poured concrete, the walls are cinder blocks and the lid is a continuous pour about 5 inches thick. This chase connects the boiler room to the adjacent building and includes a 6-inch steel steam supply main, a 3-inch condensate return pipe, 1 1/2-inch copper pipes for hot and cold domestic water and a 3/4-inch copper pipe for DHW return. In addition, there are runs of canvas-covered electrical wires that power the hallway lights, fire alarms and doorbells.

In 2022, we were asked to fix a leak on a steel condensate return pipe inside this chase. Being that the top of the chase is approximately 4 feet below grade, and it was the dead of the winter, we had very few choices. We considered using PEX tubing but feared it would get caught in the middle of the chase and could fail if the condensate got hot enough. We considered using a steam-rated hose, but it was not readily available, and we feared it might kink or tear. We decided on using 3-inch copper pipe and had to install it in six-foot sections due to logistics. We used a lot of couplings on this job.

This year, at the start of the heating season, we noticed the water usage was much higher than normal (again). This time, it was the 6-inch welded steam main in the chase. We noticed it was leaking at both ends of the pipe chase. We suspected the entire pipe was in poor condition after 71 years. We spoke to the owners and gave them the bad news; they were not happy but were pleased we were going to fix the problem.

For weeks we tried to coordinate the welder, the excavator, the weather, our own crew and give the tenants plenty of notice. We called for the underground markouts and ordered the materials. Based on all these factors, we agreed that this past Friday was the best time to start.

When I looked at this job, I was struggling to write a formal proposal. There were so many unknowns. At the time, I did not know how deep the chase was below the grass, I did not know what the “lid” of the vault was made of. I did not know if the vault was pitched. The ground is pitched approximately 7 feet from the boiler room to the adjacent building, and there is a large set of stairs that the chase runs underneath. We did not know the condition of the rest of the piping or the wires. With a lot of research, and speaking to others who have done a lot of underground heating pipes in the past, we finally felt comfortable writing a contract. Basically, the contract suggested “not to exceed.” The owners understood the unknown variables and asked us to proceed.

At 6 a.m. on Friday, I arrived at the site and cranked up the heat, thinking the system may be turned off for up to twelve hours. The excavator arrived at 8 a.m. and drove his machine from the parking lot to the area where we would be working, this took about 20 minutes, as he had to drive around the entire complex on the grassy hills and sidewalks. Oh, and he (the excavating machine) was carrying/balancing a 21-foot length of 6-inch steel pipe that weighs about 600 pounds with the chain. He immediately started digging. Once the top of the vault was exposed, we learned that the “lid” was poured concrete with no seams. The hole in the earth was roughly 25 feet long, 6 feet wide and 4 feet deep. By 11 a.m. or thereabouts, the lid was gently removed, and the pipes were exposed for the first time in over 70 years.

We did not know the condition of the rest of the piping or the wires. With a lot of research, and speaking to others who have done a lot of underground heating pipes in the past, we finally felt comfortable writing a contract. Basically, the contract suggested “not to exceed.” The owners understood the unknown variables and asked us to proceed.

We immediately learned what they did in the 1950s. They used 1-inch steel pipe to support the 6-inch steam main about every 8 feet, and every one rotted and fell. They used 3/4 inch steel pipe to support the domestic pipes, all but one failed. I found this odd, as the steel condensate return and the steam main lasted about 70 years.

Over the course of the weekend, we removed and replaced 45 feet of steam main and insulated the same with 2-inch thick pipe insulation. We installed new domestic piping and insulated that, too. We ran a 2-inch length PVC pipe for future use. Basically, every pipe in the chase was replaced. We installed new supports for all the piping, hopefully our supports and piping last as long as the original installers.

In addition, we replaced all the steel piping at and near the condensate station, as most of it was rotted. Some of the piping was so bad that it fell apart when we tried to remove it.

Once the piping was complete, we performed a pressure test on all the new piping. Soon afterward, the excavator set the concrete lids back onto the vault. He sealed the joints in the lid with hydraulic cement, hoping to keep the chase dry in the future. As the excavator continued to back fill the hole with dirt, the welder finished connecting the new 6-inch steam main to the old steam supplies in the crawl space. By 3 p.m., the welder was finished, and we fired the heating system for the first time in a few days.

Needless to say, the tenants and the building owners were very happy.