OWB connection to hydronic boiler question

[Canton]

In the process of helping my neighbor connect his OWB to his indoor boiler. I've seen this done almost exclusively by using a plate heat exchanger and keeping the OWB water on one side and the indoor boiler on the other. He's convinced he wants them to be one system with shared water. I realize this will make his indoor system open to atmosphere and will run unpressurized. He will be relying on the water treatment to protect his OWB and his indoor unit as well.
Question is, is anyone here running this type of setup and what can you tell me about it?

Any info's appreciated,
Jeff.

 

[NSMaple1]

I don't think I'd do that, he would be compromising his existing system. Not just on corrosion issues, but maybe also functional ones too - sometimes system pressure is needed to get the water pumping where and how you want it to. Be interesting to hear feedback from someone who is though - if there is anyone.

 

[Clarkbug]

Is any part of his heating system in the house higher than the top of the OWB? Cause that could certainly cause an issue right there....

 

[Canton]

I don't believe there's any part of the heating system higher than the OWB. Returning water to it was actually a concern of mine. The OWB is going to be the path of most resistance - I think.

 

[hanniedog]

In a word don't do it. Actually two words trapped air.

 

[Oxford]

Man, that's a really bad idea. Opening a pressurized system to atmosphere means allowing a great deal of oxygen into what is now a closed system, adding great potential for air binding and increased corrosion due to the presence of undissolved oxygen in the system. The big issue is that it opens the internal boiler up to the possibility of a dry fire- that is, if things aren't leveled just so, the inside boiler could fire when it wasn't full of water, making it a steam boiler or worse, a flash vessel. Both of those are very bad things and are why every boiler should have a low water cutoff installed. Don't do this, but most especially don't help anyone do this. Only bad can come of it.