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Posted by HeatPro on September 03, 2004 at 08:44:10:
In Reply to: hot water circ using steam return posted by john on September 03, 2004 at 07:09:36:
It is a bad idea, as any water near steam temperature above the boiler water level can flash to steam as it drops back down off the higher level. Some 'clever' folks use the idea with mixing bypasses and tricks; but they take the chances of air entrapment, banging, condensate dirt in the loops aand pumps, and more frequent service calls to maintain the bad idea. Any leaks in gaskets, or using auto vents, introduces air and drains the line.
Install a bronze pump and lines to a heat exchanger. Take the upstairs heat zones off the exchanger with a circulator and expansion tank, just like heating a home with utility steam, and there won't be problems. The upstairs loops stay pressurized and clean. In the situation of eventually getting a hot water boiler for the bottom floors, the upstairs is already prepared. Weil McLain sells a plate heat exchanger inexpensively.