Boiler help for radiant heating

mtbikelover

We just bought a new house that has radiant in floor heating. The boiler is a cast iron. The piping is non oxygen barrier. We have a lot of rust in the water and glycol is a little low at 22%. The system is working fine.

We are installing heat in the garage so have had 3 contractors come out to look and give us a price on adding heat. In doing this, they have also reviewed our current mechanical system. All 3 have said different things - one said the system was fine and didn't really need much but doing a flush and new glycol and adding a heat exchanger would make everything work a little better and give some life to the boiler. Another said he would just do the flush and glycol and save the money on a heat exchanger ($5k) and budget for a new stainless steel boiler (approx $20k) in the next few years. And the last guy said we needed new everything (hot water heater and boiler approx $30k) or we could run the risk of having major damage.

I'm not sure what to believe so was hoping to get some advice here. I've never lived in a house with a boiler so this is all new to me.

Thank you so much in advance!

hot_rod

Yeah, non barrier tube and glycol is a bad mix. The Oxygen that migrates through the tube breaks down the inhibited hydronic glycol quickly. Did anyone check the ph of the glycol? that is the key indicator.
The fluid becomes aggressive and corrosion accelerates.

Oxygen ingress is temperature related. Low temperature radiant is safer, but your cast boiler probably runs 160- 180 or so. That temperature in any of the tube really increases O2 ingress.

How old is the boiler? What type of radiant tube? Rubber PB, or non barrier pex?

Do you need glycol? Perhaps with a garage loop it might be worth having glycol, but most homes really do not need glycoled systems..

Two choices: Use all non ferrous components pumps, expansion tank, all piping, boiler etc.

Or separate the tube from the rest of the system with a plate HX.

Regardless of the choice I would run a hydronic cleaner in the system, get all the old glycol residue out. Then start over with new fluid. Buy pre-mixed glycol, don't blend on the job unless you have DI water.

mtbikelover

Thank you Bob! Yes...PH was checked. It was 6.5-7. And yes...we need glycol. Everyone said that. It gets very cold in this region.

I believe the tube is non barrier PEX. Not sure on age of boiler but it's fairly old.

hot_rod

The glycol should be between 8-10 ph. That fluid needs to go. Info from Dow below.
Unless you have piping exposed to below freezing conditions in the home, you don’t need glycol. It’s an expensive maintenance prone fluid.

EdTheHeaterMan

OK I have experience with this, Learn about Non-Oxygen barrier tubing the hard way. Long time business customer has "InFloor" brand radiant tubing in his gypcrete floor home. The stainless steel boiler went bad and I installed a Cast Iron boiler. All good for two years. Third year the home did not get as warm. Found all kinds of red mud in all the tubes. Spent one day flushing all the tubes until red water came out. They had heat for now!

Researched the installed tubing that was over 20 years old by now, and found that it had no oxygen barrier. Now What! At that time Weil McLain was marketing a Swimming Pool Heat Exchanger; it was a SS tubing in shell design. I liked it for this project because the flat plate heat exchanger might get clogged easily over time with all the mud in the system.

I did not require antifreeze for the tubing system. Is there any reason that your system requires antifreeze? If all the floors are indoor radiant heat, you may not need it.

A few weeks later, when the weather was favorable, at no cost to the client, I installed the cast iron boiler to the shell side of the XH and the tubing to the tube side of the HX. I also spent another complete day flushing the red mud from the tubing side of the system. NOT FUN, but with some chemistry and lots of water, the tubing runs clear (no red) now. The CI Boiler side also was flushed and I’m happy to say that this boiler room is functional with no sludge or mud in the system for the last 12 years. Each side of the HX has its own auto feed, air purger, relief valve, and expansion tank. Needed to add one more circulator to move the boiler water to the HX but all the other parts on the HX side are Bronze or SS pumps and non ferrous metal fittings and valves.

I would opt for the heat exchanger. would recommend a tubing in shell over a braised plate only because the passage ways are larger. Add strainers with magnets that can be easily accessed for service. you will find some need for strainer cleaning for the first two years, but after that, the strainers will be fairly clean with proper water maintenance.

mtbikelover

Thank you very much Ed!

GroundUp

We're not supposed to discuss pricing, but $5k to add a $300 heat exchanger is ludicrous. Being largely low temp, the o2 ingress is minimal but your pH is definitely too low as is the glycol concentration. A good flush and new fluid with the proper chemistry would probably be the best bang for the buck, and set those pennies aside for a new system when the existing boiler finally dies. If you can find someone sane to add the HX, it would be the proper way to go but not for $5k on an old system.

EdTheHeaterMan

Swimming Pool Heat Exchanger

https://www.weil-mclain.com/products/swimming-pool-heat-exchanger

hot_rod

Heat exchangers work by having turbulent flow across the exchange surfaces. that turbulent flow comes form the flow rate the HX was designed for. Pool HXers are great for high flow conditions as the sheet Ed attached shows. 6 gpm boiler side, 40 gpm system side. Efficiency will really drop off with low, low flow conditions, typical in radiant applications..

Compared to a flat plat style, this small B&G needs 2.6 gpm on both sides, that is more inline with what you system would use, should you chose to separate the system. Protect it with a dirtmag or Y strainer.

I'd start with @GroundUp advise just flush and refill, keep an eye on Ph every couple years.
add a booster to it if it drops into the 8 ph range.