The conversion of low-pressure steam-heating systems to hydronic heat was investigated in 15 centrally heated buildings. The purpose of this research was to determine the costs and energy savings and practicality of this retrofit. Specific work depended on the type of steam system being converted. For two-pipe steam (TPS) conversions, the existing distribution piping could be reused, whereas for single-pipe steam (SPS) conversions, new piping and radiation needed to be installed, making SPS systems more expensive and difficult to convert. Energy savings ranged from 13% to 39% of weather-normalised total gas use, with a median of 27%. Savings were not reduced for the three cases in which existing boilers were converted rather than replaced. The median price of SPS conversion was 55,000 dollars a median payback of 33 years. By comparison, the median price of TPS conversion was 13,000 dollars with a median payback of about nine years.

KEYWORDS: energy conservation, energy consumption, steam boilers, central heating, buildings, research, costs, economics, modernising, low pressure, steam, steam heaters, payback period, converting, flats, multistorey buildings, USA, comparing.