> I vaguely remember coming across a furnace once that I think vented
 > steam and condensate to the atmosphere instead of recirculating it. That
 > could have only meant it was rather low pressure. As far as I understand
 > boilers, if it uses a safety relief valve, it requires some IQ and a
 > license to fix it.
All boilers, even home-heating hot WATER boilers require relief valves. It's 
the setting that determines if it's "high pressure" or "low pressure". 
Actually, I think the steam guys refer to "medium pressure" too.
Hot water systems will have air-release valves that allow air bleedoff, and 
it's not uncommon to have a steam leak in an old building. But I can't 
imagine a heating system where the steam is deliberately allowed to escape. 
Not only would the efficiency be horrible, but the boiler would get scaled up 
in a BIG hurry.
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