Tips on Balancing One-Pipe Steam Systems

Since George D. Hoffman invented the first float-and-thermostatic steam air vent in 1912, we’ve learned a thing or two. We’d like to share with you a few one-pipe-steam balancing tips we’ve picked up along the way.Vent the mains quickly. If you want the steam to arrive at all the radiators at about the same time, you must vent the mains quickly. Steam is a gas and it will always look for a way out of the system. When it leaves the boiler, it heads toward the air vents. The bigger the air vent, the more inclined steam will be to head that way. If your system heats unevenly, install a Hoffman #75 main vent near the end of the main and marvel at the difference it makes.

The #75 vent should be at least 15 inches back from the end of the main and six to ten inches up on a nipple to keep it away from any end-of-main water hammer. The bigger the hole, the faster the venting, so it pays to install a tee with a 3/4 inch tapping for the vent near the end of the main. Don’t try to get by with a tiny hole drilled into the main.

Install a Hoffman “Y”strainer vertically before the main vent. We don’t have to tell you how dirty an old steam system can be. Since the steam is moving at high velocity (typically, about 25 mph in a one-pipe system), it picks up particles of rust and sediment. Eventually, this stuff winds up inside the main vent. Before long, the main vents clog and can’t shut. They spit water and let steam pass to the atmosphere. This creates water-level problems at the boiler.

Vent the radiators based on their size. If your goal is to get all the radiators hot simultaneously on the coldest day of the year, you’ll have to handle the air in a special way. First, as we said before, vent the mains quickly. That’s important. Then vent the radiators in relation to their size, not necessarily their location in the building.

The main vents will make sure steam reaches each radiator at about the same time. Since big radiators contain more air than small radiators, big radiators should have larger air vents than small radiators.

Hoffman’s 1-A vent, with its adjustable venting rate, is an. excellent choice for systems with radiators of different sizes.

Insulate the steam lines. When steam condenses and turns back into water, it stops moving. That’s why the old-timers spent so much time insulating their steam mains. They wanted the steam to condense in the radiators, not in the basement piping.

If someone removed the asbestos insulation, you must replace it with a more suitable material if you want a balanced system. Uninsulated steam pipes have about five times the heat loss of insulated steam pipes.

Wrap the pipes well so the steam has a chance to get where you want it to go.

Clean the system. If the boiler water is dirty, the steam will carry water with it when it heads off into the piping. This leads to water level problems at the boiler, sure, but it also creates balancing problems throughout the system.

The steam gives up its latent-heat energy to the mist of water that’s traveling with it. That stops the steam dead in its tracks. The far radiators remain cold while the radiators near the boiler room get warm. The burner often short-cycles when he steam quality is poor. This, too, leads to balancing problems.

Check the boiler manufacturer’s cleaning instructions. It can take a day or two to get a boiler’s water back in “clean-steam” shape, but this is often the only solution to those balancing problems.

Lower the steam pressure. Steam heating systems ride a wave of pressure from the “cut-in” to the “cut-out” setting of the pressuretrol or the vaporstat. The system must cycle up and down on that wave because that’s how the air vents work.

Steam pushes the air from the vents; the vents then shut on temperature. When the steam condenses, the vents are supposed to open to allow venting to continue. But if the system pressure is too high, the air vents might stay closed. Since air can’t escape from a closed air vent, the radiators stay cool, and the system goes out of balance.

The air vents and the pressuretrol or vaporstat work together to move the air from the system. If you set the “cut-in” setting at one-half psi on a pressuretrol or at about four ounces on a vaporstat, you’ll never lock the air vents closed.

The “cut-out” pressure should be as low as possible. There is no reason to raise the steam pressure any higher than it has to be. High-pressure steam actually moves more slowly than low-pressure steam.

So when you’re trying to balance that one-pipe system, lower the pressure.

Proper near-boiler piping also plays a huge role in the one-pipe-steam balancing act. Always follow the boiler manufacturer’s specifications carefully.

Your Hoffman representative is well versed in steam-heating-system problems and their solutions. If you need help, call and ask for their advice. They’re always there for you!

Reprinted from CounterPoint January 1996, Vol. 3, Issue 1