recovering heat from condensate for domestic hot water

Rob Sisk_2

Does anyone have any thoughts/concerns on the idea of gravity-feeding the condensate return from a two-pipe steam system through an indirect water heater to preheat domestic hot water?
The alternative is to pipe supply and return lines from the indirect water heater to opposite sides of the boiler water chest below the water line, but this requires a circulating pump.

Rich W

Be safe

With every heat exchange comes a loss in efficiency. Plus, you'll need to make up for those lost Btu's back at the boiler. I can't think of a way to do what you want without a circ/ heat exchanger in the first place- unless you run the return through the flue passage of a water heater...

You could use one of those vent pipe heat exchangers to recover heat going up the chimney. Just be sure to monitor the flue gas temp- and turn off the circ before the temp gets too low. Now you need to worry about flashing to steam in the copper coil of the heat exchanger when the circ is off... With my KISS up bringing, I would plunk a bare steel tank with a relief valve next to the boiler and send the outlet of that to the inlet of your WH. A lot of control work could overcome the problems. I don't think it's worth the effort in this case.

Low flue temp was one of MANY problems at this job. The guy is a builder and thinks this stuff is something you can go ahead and "Just Do It". There was a 3" passage in the vent pipe from the wood stove. How safe is that?