Indirect water heater as steam(water) to hydro zone HX (poor heat transfer)

wcs5050 · December 14

My heat exchange from 200k res steam boiler set at 190degF to a 30 gal superstor set at 180degF is pathetic… looking at interior water quality after replacing a circulator I’m suspecting the SSU30 corrugated coil is totally fouled. Tank is 11 yrs old now. I inherited (as the service babysitter) the setup about 2 yrs ago. I’m considering a TFI Everhot external water heater, but also considering perhaps just a different brand of indirect tank… I’m done with HTP.
There is about 45k btu hydronic load connected.
I don’t want to turn up boiler water limit because I’m already getting passive steam heating when not requested, and the system is already wasting so much gas/energy.

Can anyone weigh in some thoughts.

Thanks.

mattmia2 · December 14

clean the coil out with acid then raise the ph on the boiler so it produces little mud. pumping the coil full of mud isn't HTP's fault.

if you are just using it as a shell and tube hx you could run it the other way, put the boiler water in the tank and run the hot water loop water through the coil, then there'd be a lot more space for the mud.

Jamie Hall · December 14

Changing to a different brand of heat exchanger or even an indirect is not going to fix the problem: 11 years of lack of maintenance. As @mattmia2 suggests, spend a little time and effort to clean and descale the poor thing, and flush it out a couple of times.

If you do decide to splurge instead and spend a lot of money on a new system, also decide to maintain it properly so you're not there again in a few years.

wcs5050 · December 14

I am the technician/operator that recently inherited care of this neglected system.

I wasn’t clear…I’m seeing significant fouling on the hydronic side of the system not the steam side… I expect steam side sludge… it has had wet side clearing service and water treatment, but I can absolutely appreciate the possibility of sludge on the inside of the coil.

If anyone has cut open a superstor specifically, they will see the outside surface of the coil is fin-corrugated. I’m suspecting this is caked up. I’m pretty sure this system ran for years without adequate water content and/or functional air elimination. I’m trying to rehabilitate it now.

I’ll be sure not to speak lowly of brands in the future. Thanks for the check. Not a good look.

wcs5050 · December 14

What I meant was, I’m considering changing to a different brand/style of indirect that has smooth faced coil.

wcs5050 · December 14

To cleanse the outer face of the coil would be impossible now, wouldn’t you agree??

mattmia2 · December 14

you could possibly loosen it up with acid and flush it out. does stuff come out of the bottom tapping of the tank? the better question is why is a hot water system making so much sludge?

wcs5050 · December 14

That was my question as well. Small pex radiant zone via mixing valve, and small fin tube baseboard zone. There is hardly any iron in the system. Maybe isolated to the circulator by low water content and poor air elimination.

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wcs5050 · December 14

Flush attempt on coil inside is a worthy endeavor because the hydronic setup barely achieves 130degF in 20degF outdoor.

mattmia2 · December 14

leaking and a ton of makeup water will do that.

Jamie Hall · December 15

oxygen barrier PEX? I hope??

mattmia2 · December 15

https://forum.heatinghelp.com/discussion/comment/1877313#Comment_1877313

or that

hot_rod · December 15

the sludge would be on the part of the indirect connected to the boiler. If that is the coil, then that is the sludged portion

If the tank is just the hydronic water, mineral scaling is possible. That is generally from ongoing fill water being added

Descaling the outside if the coil is not so easy

At that age??

Go with a smooth coil rank

Laars, bradford white, Lochinvar, Bock are some brands

mattmia2 · December 15

whatever rusted the circulator is going to rust a steel tank too.

wcs5050 · December 15

Thanks everyone. Very good points.

The pex appears to be the first stadler viega orange/white which I believe is barrier. Good call on that anyway. I have another job where I recently discovered bon-barrier on some radiant, after progressively changing noisy circulators that grew rust into the impeller.

I have make up water off at the moment and it appears to be holding steady.

I was looking at Bradford white or Ideal. Both are all stainless with smooth outer coil.
I’ll def be cutting this one open to see what the coil looks like.

mattmia2 · December 16

what are the temps at the 4 ports of the tank?

hot_rod · December 16

you are sure both circulators are spinning?

The coil could thermosiphon from the boiler imitating a plugged coil?

bjohnhy · December 16

https://forum.heatinghelp.com/discussion/comment/1877444#Comment_1877444

You could just drop an endoscope camera down the TPV orifice. But that doesn't seem as interesting as cutting it open

mattmia2 · December 16

https://forum.heatinghelp.com/discussion/comment/1877476#Comment_1877476

it is a superstore

wcs5050 · 12:07AM

Hydronic circ for sure turning. 3 speed Grundfos on steam loop showing water hammer at quick close of ball valve.
190 at coil supply, 5-10 below on coil return. With hydronic flowing barely getting to 130. If I close off supplies tank slowly recovers… I mean slowly. Worth looking in on the primary/coil circ I suppose.
$40 coil in there, $200 labor ;)

hot_rod · 12:13AM

This was my experience with a finned coil tank, less than 1 year into the tank the owner started to notice DHW production falling off. I did the boiler work, a different plumber supplied the indirect. Guess who sorted it out.

Yes it was hard water, but…

mattmia2 · 12:45AM

https://forum.heatinghelp.com/discussion/comment/1877818#Comment_1877818

if the coil is removable you can dip it in acid and clean it. or maybe get 2 and rotate them. only $40 for the coil? put anti seize on the bolts so it comes out again later.

mattmia2 · 12:46AM

but as far as i know the coil on a superstore is not removable.

Indirect water heater as steam(water) to hydro zone HX (poor heat transfer)

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