Noel Murdough
If your steam system is noisy and inefficient, it might help to learn about the system and understand what it can and can't do.
The system and the boiler itself are two different items. First, I'll discuss the boiler. Old boilers were self contained, in that they had a large open space at the top to separate the steam from the water within the boiler. This was known as the "steamchest". New steam boilers don't have this space, and the risers, header, and equalizer connected to the boiler serve this purpose. As the water leaves the boiler it is moving at about 30 miles per hour, and it moves with the steam. As the piping heats up, the steam has to compress what is ahead of it, and it slows down. The water falls out of the flow and is returned to the bottom of the boiler, through the equalizer. The steam that leaves the boiler is lighter than air, and it rises into the building piping, or the "system".
When the boiler is off, the waterline in the boiler will match the waterline in the gauge glass. If you replaced the tankless coil with a plate of glass, you could observe this. When the boiler is making steam, there is no waterline within the boiler that matches the waterline in the glass, the water is violent, and is all of the way up in the risers, and the gauge glass is only a representation that the same WEIGHT of water is in the boiler as would show in the glass if that same weight of water weren't steaming. Think of a balance beam with a container of water balancing a container of foam on the other side. To balance, the foam would occupy much more space than the water would. The weight would be the same on each side.
This demonstration next shows what this same boiler looks like when it runs with oily water in it. The demonstrator poured a couple spoonfuls of cooking oil into the boiler, to simulate a boiler that wasn't cleaned before it was put into service. That's the only change from pictures 1-4. Pretty violent, isn't it?
Not only does it cost a tremendous amount of energy to lift that much water up into the house (compared to only lifting a little water into the header only), that 210° water is being replaced at 30 miles an hour with 60° water from the returns. Any water that leaves with the steam does NOT return down the equalizer to blend with the cold return water. It's pretty hard on the boiler.
If your piping is correct at the boiler, and the boiler water is clean (it bounces in the glass less than half an inch), we can evaluate how your system interacts with the boiler. The most important thing to know will be the amount of radiators (in square feet of surface area) and the amount of boiler output. If these two numbers don't match somewhat, the system will have problems that are hard to overcome. Check your boiler rating plate for steam output; measured in sq ft. That is how many square feet of radiator it will heat. Piping losses don't need to be figured unless they are unusual, the manufacturer already figured in 33% for the piping. Measue the radiators to see how they compare.
If the steam pipes are uninsulated, they are too small. The original installing company had to decide whether to insulate the pipes, or increase the size by TWO pipe sizes. They NEVER chose to increase the pipe size. It will be easier for you to reinsulate your existing piping than it would be to increase all of the mains two pipe sizes.
With the mains insulated and the boiler making the right amount of dry steam, we can look at the air venting. From the second that the header becomes hot with steam, the supply mains should fill to the last take-off within about 1 to 3 minutes. The main air vent or last steam trap should become steam hot, then. If it takes much longer than that, you could save some fuel (run time) by increasing your main vent capacity. Your steam is compressing air, rather than flying into radiators. $$$
Once you can get your mains to heat within a couple minutes, it's time to think about balancing the radiators. If you have 2-pipe radiators, click here. If you have one pipe radiators, balancing by air vents on each radiator is next. You'll need to set the thermostat at one number and leave it there for a couple days to get the balance down pat. This gives a chance for a slow to heat radiator to show up after many cycles as a cold room. That radiator will need a slightly faster vent rate. You can either use adjustable vents (begin with them set wide open to start) or swap around the existing radiator vents to get fast ones where they belong, or you can buy new ones to fit the circumstance.
Once you achieve good balance, quiet system, and lower fuel costs, you can think about a setback thermostat. Keep in mind that the system is now running quietly, when your system comes roaring out of setback. All of that cold iron is going to make noises in most cases, as it heats up. Those noises are unavoidable. The system was designed to be warmed up by a woman lighting a small coal fire and adding to it as the day went on. That can't be duplicated by a single firing rate burner and a thermostat that just slams it on. What noises the setback thermostat causes can only be solved by changing the setback thermostat settings.