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ECM: Space Heating & Cooling

H8. Convert Steam Heating to Hot Water Distribution


Steam-heated buildings use more energy than buildings with hot-water-distribution systems. This is because with steam heat, the boiler must heat the water to the point at which it becomes steam, which takes much more energy than heating water just enough for a hot water system. In addition, steam-heated buildings often have the problem of uneven heating, which is a big cause of energy waste in multifamily building because maintenance staff have to overheat some apartments to provide adequate heat to others. Therefore, converting a steam-distribution system to hot water can save energy as well as reduce problems with maintenance and uneven heating of rooms or apartments. 

There are two types of steam heating systems: single-pipe and two-pipe steam systems. With single-pipe systems, steam travels from the boiler to the radiator, fills the radiator and condenses; this condensed water then goes back out of the radiator through the same pipe, eventually to return to the boiler. In two-pipe steam systems, steam enters the radiator through one pipe and leaves as condensate through another pipe to return to the boiler. The radiators of two-pipe steam systems are very similar to those of hot water systems and can be kept and used in the new system, with a few minor changes. Single-pipe steam radiators, on the other hand, require the expensive addition of a second pipe during a conversion. For this reason, it is generally more cost-effective to convert a two-pipe steam distribution system than a single-pipe system.

When converting a system from steam to hot water, the boiler does not necessarily have to be replaced. If the existing boiler is in good condition and able to withstand the maximum water pressure of the proposed system, then it can be converted to be compatible with the new system rather than replaced. However, if the existing boiler is old, inefficient, and oversized, as is often the case, replacing the boiler may be the best option. Steam-to-hot water conversions generally reduce the amount of maintenance needed because hot water systems require less maintenance than steam systems, and residents have fewer complaints about overheating or underheating. Nevertheless, the maintenance staff will need to become familiar with the operations of the new system and any controls that are installed.


  • Multifamily buildings with steam heat 


  • Single-pipe
  • Two-pipe


  • Pipes should be pressure tested before conversion to reveal any seam leaks.
  • It is generally more cost-effective to convert a two-pipe steam-distribution system than a single-pipe system.


  • Converting single-pipe systems to two-pipe systems can reduce heating costs approximately 13-27 percent.
  • Replacing steam boilers with hot water boilers can reduce heating costs approximately 16-39 percent.
  • Replacing older, inefficient boilers can reduce annual heating costs approximately 20-45 percent.


Energy Conservation for Housing – A Workbook, HUD, September 1998. Pages 7-71 through 7-73 address converting steam heating to hot water distribution.

Improving Energy Efficiency in Apartment Buildings, American Council for an Energy-Efficient Economy, 1995. ISBN 0-918249-23-6. Pages 76 through 83 address converting steam heating to hot water distribution.

Energy Performance Contracting for Public and Indian Housing: A Guide for Participants, HUD, February 1992. Page 25 address how to use convert steam heating to hot water using performance contracting.

Heat Distribution Systems: Steam Radiators, Part of the U.S. Department of Energy's Consumer's Guide. Discusses the problems caused by steam heating.

ENERGY STAR Program: Heating and Cooling, Provides information on high-efficiency products, tips on finding a contractor, and guidance on sizing and installation.