heat exchanger vs chemical for non barrier tubing looking for low delta t

Adk1guy

I have several items at issue. To use a heat exchanger or continue to treat with chemical. If a heat exchanger then the lowest delta T across the heat exchanger. Then how to make this system compatable with a condensings propane boiler in the future.
System: heat way orange rubber tubing staple up. steel tube boiler, cast iron radiation, steel pipe.
Been treated (not religiously) with steam master pellets. After they went off the market rectoseal 8 way.
Options I see are continue chemical treatment or isolate the non barrier tubing with a brazed plate heat exchanger.
The system requires 140 degree the great room (high cathedral ceilings, big windows) in our coldest outdoor temperatures. Cast iron radiators are big and do fine at 140. But my watts mixing valve has a delta of t of 20. I guess I can pull it out but I like the protection against high temp. Like I might have to call someone if I am out of town and my boiler goes down. We all know how that goes. Do they send an "A" guy or a "D" guy. Do they even have "A" guys. This could go onto a different thread but the experience it takes to be a good tech combined with low pay, bad hours, poor working conditions... no wonder good techs are scarce.

So the short of it. Chemical vs heat exchanger. How to size the heat exchanger to the lowest feasible delta T with 110,000 input and 75,000 output. I have seen the formula and I suppose could plug in the numbers but I am hoping for a answer from someone who is adept at using the formula.

mattmia2

You could swap the thermostatic mixing valve for one of the Taco electronic mixing valves, that would take away the need for the heat across the thermostatic element to actuate it.

The HX would be my preference, it will be more effective at protecting the rest of the system than chemicals but you do have to get the transfer engineering correct and you will lose some of the ability to run in the condensing range of the boiler, although that may cost far less than chemicals and the damage to the ferrous components of the system.

EdTheHeaterMan

I have come across this once in my history of service. The "InFloor Company" sold a non-barrier PEX system in the 1970s and used a stainless steel boiler with all non-ferrus fittings and components. I did not realize this when I replaced the boiler with a cast iron WM gold GV boiler in the 1990s. Within 1 year the tubing was clogged with red mud. I found out the hard way that the O2 barrier was important. The fix I came up with was to use a stainless steel "Pool" heat exchanger (because the passageways were substantially wider than a braised plate HX) and flushing the mud from the system. This was a several-day project in the middle of the winter for a customer that did not even buy oil from me! But his business purchased a substantial amount of off-road diesel for years before... so he was kind of a loyal customer.

The Heat exchanger idea I believe is the best in your situation. just be sure to use SS or bronze pumps and non-ferrus air eliminators and fittings as needed.

Respectfully submitted,
Mr.Ed

hot_rod

Both!
The SS hx will protect the boiler side. But some of that tube allows O2 in and you will sludge the HX, so adding some O2 scavenger will maybe help prevent frequent flushing of the B side from the tube sludge.

I agree with @EdTheHeaterMan a properly sized tube and shell HX may be better. A small indirect tank can be a good HX at a reasonable cost, and you get some "bufferin". Install it with some purge valves like you do with tankless water heaters to allow easy flushing. The Webstone Purge ball valves are nice for that.