heat exchanger needed for combining old & new systems?

SomeTradesJack · October 5

DIY homeowner here. Gutted the 1/2 the downstairs and put in radiant/gypcrete. The wife wants to keep CI radiators on 2nd floor, which was factored into the design.

Two questions:

Should I use a HX to isolate the new system parts (and my spendy Navien boiler) from 130 year-old cast iron/galvanized stuff that is filled with black water? Original boiler was a coal stoker. I am going to zone the 2nd floor and say adios to the 3" pipes in the basement, so there will be somewhat less circulating gunk eventually.
Is there a way to clean the old system? I've tried flushing/draining and that accomplished next to nothing.

Thanks!

EdTheHeaterMan · October 6

This is done all the time. First Q>. did you use Oxygen barrier PEX in the Gyp-Crete?

If yes to Oxygen Barrier Tubing, then you do not need a HX to separate the old from the new.

There is a device called a Dirt Mag. that you place on the return pipe near the boiler to trap any dirt and old suspended iron particles. the Magnet part traps the iron and the strainer traps the other dirt. once a year, you can drain off any dirt by opening the valve at the bottom and removing the magnets during the FLUSH.

Great Minds think alike and at the same time @mattmia2 8:01

mattmia2 · October 6

No need for a hx if your tubing is oxygen barrier. A magnetic dirt separator would be a great idea to protect the circulators. Unless your old emitters are really oversized you will need to mix down cooler water for the radiant.

EdTheHeaterMan · October 6

Suppose you do not have Oxygen Barrier PEX, the nyou need a HX to separate an iron boiler from the rest of the system. If you are using a stainless steel boiler than no HX needed, but all the pumps and other accessories need to be Stainless steel or Bronze.

After you determine that, you will need two temperatures form that boiler at the same time. In the event that both the high temperature Radiator zone and the low temperature PEX zone calls for heat at the same time.

Here is a booklet you will want to read to know how to do that. https://s3.amazonaws.com/s3.supplyhouse.com/product_files/108119-Reference%20Guide.pdf . Zoning with two temperatures starts on Page 24 in this booklet. There are other good sources available to find different ways to do that.

SomeTradesJack · October 6

Thanks—

Yes, I used HePEX.

Hoping to run water temps of 140 for CI rads. Design predicts 114-127 degrees for in-floor.

I'll definitely get the Dirt Mag.

Thanks for the brochure, Ed. Very informative. The writing is much like Dan H himself! 😀

hot_rod · October 6

I would still run a hydronic cleaner in the system for a day. Drain, flush, and fill with water that meets the Navian spec in the installation manual

EdTheHeaterMan · October 6

https://forum.heatinghelp.com/discussion/comment/1813169#Comment_1813169

Very much like Dan H. because he wrote it!!! At the time when he worked for a B&G Rep for the NYC area, they commissioned him to write it. But he does not own it and his name was never associated with it. He tells the story that when the booklet was finished, the engineers at B&G didn't like it…. His Reply was "I didn't write it for you!"

heat exchanger needed for combining old & new systems?

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