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Posted by HeatPro on September 01, 2005 at 20:04:13:
In Reply to: alternative coal boiler in resident posted by Dan McCartney on September 01, 2005 at 17:23:19:
Pipe them in parallel so you can use one and not have the other waste heat from the jacket and up the chimney while it is off. A good piping arrangement is the primary-secondary, where either boiler can add heat to the house without complicated control.
You can also repair one by shutting isolation valves. If necessary, the gas boiler can cut in right away on a set back thermostat setting so the house will stay warm.
You also must have separate chimney flues, as they work at different pressures while they burn the different fuels. You don't want the products of one to go backwards through the other into your home.
http://www.woodboilers.com/piping-layouts.asp