No oxygen barrier

jeff4444

I have a staple up radiant floor system 30+ years old. It is approximately three-quarter inch tubing without a radiant barrier. It works well with 130° heat water.

After rusting out the initial steel propane boiler, and some replaced warranty parts, like a Built in indirect heating tank twice, I installed a propane fired water heater as the new heat source. 

These seem to last about 10 years before needing to be replaced, but not from rusting out. These fail from eventual burner problems, etc. 

So in someways, I feel like I solved the oxygen barrier problem. But when the current water heater fails should I be thinking about a condensing wall hung boiler? Is the heat exchanger in modern boilers like this stainless steel such that the oxygen in the water would not cause the boiler a problem? Or are there specific boilers that this is the case for?

I should also note that there is high iron in our water as well as other minerals. The iron tends to gunk things up somewhat as well, so that is an additional problem and works against using a plate heat exchanger, which I tried early on.

Thanks for any ideas. 

Larry Weingarten

Hi, The first thing that comes to mind is to install a heat exchanger between the tubing and the rest of the system. This would eliminate the oxygen problem. Have you considered that?
Yours, Larry

jeff4444

Yes, in fact, I tried a plate exchanger early on. There’s so much iron and gunk in the water that circulating around and round and round it plugged up the heat exchanger. That was one of the attractions of using the hot water tank.

kcopp

An indirect water heater would prob do the trick..

Or https://www.tfi-everhot.com/external-tankless-water-heaters.html

Lots of surface area. All copper.

Furthermore EVERY part on the Non barrier side should be Non ferrous.
I would also add a inhibitor.

hot_rod

A good power flush, with a flow velocity of 5 fps or more is needed to flush out heavy particles and sludge.
I'd hit it with a good dose of hydronic cleaner first to soften up the sludge.

Next, either isolate the tube with some HX, or use all non ferrous components. I'd keep an oxygen scavenger chemical in the system. Check and boost it every few years.

Hydronic conditioners will do this. Or the outdoor wood boiler people sell basic O2 scavengers by the bucket

The lower the system operating temper the slower the O2 ingress. Although many rubber tube systems, or any non plate radiant tend to to run high temperatures to get the job done.

jeff4444

thanks for the ideas. @kcopp - The indirect water heater with full shell hx is very interesting. No small channels to get clogged up. I guess the question there is to look at cost of new boiler and indirect water heater vs. current program of just replacing high quality water heater every 10 yrs or so.

@hot_rod - power flush and chems. seems like a good idea if I can find the right guy to do it.

Ironman

You could also use a sufficiently sized tube and shell HX like what’s used for swimming pools.

jeff4444

shell and tube is something to look into, thanks.

hot_rod

jeff4444 said:

shell and tube is something to look into, thanks.

If you go with a shell and tube or any other HX, get it sized properly.
Those swimming pool HX are not usually good for hydronics like yours. They are designed for huge delta T's. Boiler at 180, pool at 80F, and high gpm flow rates.

jeff4444

Something new on this - Looking at condensing wall mount boilers - I saw people recommending the Triangle Tube Prestige Solo.

I skimmed the install manual and noticed they say it is OK to use it with non O2 barrier radiant tubing because of the heat exchanger it has. This may be a viable option when its time to replace the existing heat source...

https://www.supplyhouse.com/Triangle-Tube-PA110-86000-BTU-Output-Prestige-Solo-110-Condensing-Gas-Boiler-w-ACVMax-Control

hot_rod

If you use non barrier tube, everything in the system needs to be non ferrous, not just the boiler.

Pumps, expansion tank all pipe, valves, fittings.
It ends up being less $$ to use barrier tube. Stainless pumps for example are big $$

jeff4444

It’s been running for 30 years with ferrous pumps and a little bit of cast-iron. Mostly copper. Only problem I had in the past was steel boiler rusting out. So it seems the boiler was the main issue. 

hot_rod

Seems like some odd wording about non barrier tube. It states Ok to use with non barrier, just not with their steel tank
To me that tell that any steel or iron used will corrode. that combined with your high iron water. Doesn't sound like a great mix.

It would be interesting to see how they would handle warranty on a boiler connected to non barrier tube, with ferrous metals.

Check the fill water also.

jeff4444

Yes, that tank part is interesting. I can’t find too many details on the tank but at least the “inner tank“ is stainless steel so that is better than no stainless steel I guess. Possibly the outer tank is not stainless steel and they’re worried about that. Can’t tell from what I can see.

you probably remember from earlier that when I first installed the system, it was with a steel boiler which rusted out. Then I put in a direct vent, propane water heater, which lasted 10 years. Interestingly it did not rust out, but the burner and some combustion components failed. I replaced that with another direct vent propane tank six years ago, so it probably has another four years or so on it. 

I figure the water heater tank is made for constantly fresh, incoming water, always bringing in new oxygen. So the non-barrier tube doesn’t seem to bother it.

hot_rod

Tank type water heaters are glass lined, so they are fine with O2 ingress
Tank water heaters fail because the condense constantly at low temperature and rot away the burner components. Sometimes the flue piping

If the steel outer tank of that indirect could rust away, couldn’t also a steel expansion tank?

Seem like they should add some caution to that statement, a foot note or something.