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[doo_hicky]

ok, soooooo plumbing these HX's in series would go like this:   Supply line into DHW HX port 1 out of port 2 then into oil boiler HX port 1 out port 2 then straight shot back to my wood boiler, is this correct?

Mike 

[slimjim]

Yes and don't forget on the other side of the heat exchanger, the flow should be counter current, in other words the flow through each heat exchanger should go in the opposite direction on the pressurized side.

[doo_hicky]

Yes, I understand about the counter flow.  learned about it from on here, and people having issues.

Hope I can plumb them both tonight after work and hopefully running by the weekend.

I'll keep everyone posted

thanks again

Mike

[doo_hicky]

I have been thinking about what Jim was saying about having an issue if/when the power goes out and having heat/pressure build up in my boiler.

Could a soultion be a zone valve that(which one normally open or normally closed???) would open when the power goes out.  Is there such a beast? 

I feel this has merit because my trunk line comes out of the top of the boiler before it goes into my PexalPex.  I have a T there already for future expansions, and hotwater will circulate without power.  Ill just put in a section of finned radiator in a loop before it returns to the bottom of the boiler.

Thoughts?? or am i off my rocker?

[slimjim]

You are exactly right, is the building being used heated already, can you tag onto an existing loop above the boiler?

[doo_hicky]

Well, I did it.

Fire in the furnace and no leaks!!!!!  Hot domestic water.  Now to tie into exixting boiler.

When the HX is "working" what would be the maximum temperature drop that one should see?  Just getting an idea if I need to bump up the speed of my pump.

Thanks, this forum has been a GREAT help!

Mike

[slimjim]

I don't like to see more than 20 degrees under full load.

[doo_hicky]

OK, I thought that was what the average was.

Thank you for the confirmation.

[doo_hicky]

Well it's been a little over 2 weeks and everything is working better than expected.  I can go 12 hours before I need to reload, this was verified when we had a couople days of single digits.  My idea of using a lower hot water tank thermostat to complete the circuit for the oil boiler burner works like the expensive strap on aquastats.  I just have it sitting on top of the HX for the bioler and if the fire would ever go out and the temp of the HX drops below 125 the circuit is completed and the oil burner will kick on.  I completely shut off the electric hot water tank, it had a little blinking light that was annoying me(to warn of high temps).  I was pushing 180 deg water to the house, but backed it off to 170-175.

My only complaint is the smoke,  depending on how the wind blows...... I may add a nother section or 2 to see if that makes a difference.  My long term goal seeing that this furnace is working so well, I have made up my mind to do a block chimney next year. 

Mike

[slimjim]

Glad it all worked out well for you, have a very Merry Christmas!