Converting From Steam To Hot Water

July/August 2009
A version of this article appears in the July/August 2009 issue of Home Energy Magazine.
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July 01, 2009
Q . Is it feasible to retrofit cast-iron single-pipe steam radiators to work on hot water from a new combined heating/domestic hot water (DHW) system?  And if so, would it ever make sense to integrate that into a solar hot water system (SHW)?  I’ve heard that hot water radiators are more efficient than steam in the San Francisco Bay Area. Tom White Home Energy Magazine Steve Greenberg replies: STEVE GREENBERG  is a facilities energy management engineer at Lawrence Berkeley National Laboratory and a technical editor at Home Energy. A. Such a retrofit is possible, but you might need more area (bigger radiators) if you’re using hot water rather than steam, mostly because the water isn’t as hot as the steam, and partly because phase change heat transfer (that is, condensing steam) is more effective than convection (that is, hot water in the tubes); note that the effectiveness of the heat exchanger is not the same as system efficiency. But if the conversion is being done at the same time as the house is being tightened (better windows, insulation, and so on), it might work well with the existing radiators. ...

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