Maintenance Tips to Keep Your One-Pipe Steam System in Tip-Top Shape

With energy costs at record levels, efficiency is on the minds of building and homeowners everywhere.  And, as cold weather starts to creep into many areas we get numerous questions about all types of steam systems.  The subjects range from what causes water hammer in steam systems, to the proper sizing of traps and pressure reducing stations, to selecting boiler feed tanks and condensate pumps.  So, in order for us to be more efficient, save energy and money while heating your house this winter we’ve created a list of some common “do’s” when working on a one-pipe steam system.

DO size a replacement boiler by counting all of the radiation in the house. The total becomes the Net EDR (equivalent direct radiation) rating of your replacement boiler. Steam does not care about heat losses-or anything else- except the amount of cold metal attached to the boiler. If the boiler is too small, part of the building will never heat. If it is too big, the new boiler will short cycle like mad, consume bodacious amounts of fuel and create service calls.

DO pipe the boiler according to the instructions from the boiler manufacturer. New boilers are very different from older boilers. The sections are narrower, the exit holes are smaller, there are fewer of them, and the steam chest is almost non-existent. So pipe them according to the directions and you will save yourself a lot of headaches down the road.

DO skim the boiler according to the boiler manufacturer’s instructions. Oil from the foundry as well as the cutting oils used out in the field will create surface tension on the top of the water in the boiler. This sets up a foaming/priming condition that creates very wet steam. The results are water hammer, lack of heat and unhappy residents.

DO use adjustable vents based upon the size of the radiator. When coal fired systems were converted to oil or gas, we found the system operated differently. To adjust to this new “on & off’ type system, we had to balance the air venting of the larger radiators versus the smaller radiators. It had nothing to do with the location of the radiator.

DO use the largest main vents that you can get. By venting the air from the main separately and quickly, you will significantly improve the balance of the system. By using a large vent, the steam will head toward the end of the main before it starts filling the risers. This provides balance to a one-pipe system.


DO use a steam pipe-sizing chart that tells you the exact pipe size needed to support the amount of radiation connected to that riser. The pipe that connects the steam main to an up-feed riser is called a horizontal run-out. Its job is to simultaneously supply steam to the riser while allowing condensation, which is coming back from the radiators, to drain back, by gravity, into the steam main. If the steam is moving too fast, the condensation won’t be able to drain back into the main: instead, the steam will drive it towards the radiator vents.


DO keep the pressure trol or vapor stat set as low as possible because:

  • Low-pressure steam moves faster than high-pressure steam. If you want the steam to reach the end of the main quickly, lower the pressure and make sure you install a large capacity main air vent.
  • All radiator vents have a “drop-away” pressure rating. This is the maximum pressure that the float inside the vent can fall down against, reopening the vent. If the pressure trol setting is too high, once the vent closes it won’t be able to reopen to vent any remaining air in the radiator.
  • One-pipe steam radiators were sized to heat the space on the coldest day of the year with less that I psi of steam. For every square foot of EDR, the radiator will emit 240 BTU/H when the room temperature is 70°F and the steam temperature is 215°F.

While there are also many don’ts, if we focus on the do’s, it will help achieve peak performance levels.

Helpful links:

Steam Calculators

Steam Specialty Component Selection

Steam & Condensate Properties