Converting from propylene glycol to ethylene glycol

Homeowner96

My heating system is about 8 years old now and was installed using Noburst -100 propylene glcol as the heat transfer fluid. Glycol was selected as I have some piping running in external walls and unheated sections of the house. Propylene glycol was selected because a boiler mate system was proposed as a future add to replace the domestic gas fired hot water heater. My system was installed using the Viega ProPress fittings so suffers from the micro leakage corrosion issue at most of the joints. There has been plenty of discussion around ProPress and glycol and I am not interested in started another thread with that as a topic...I have what I have.

I need to drain down most of the system to do some expansion and was thinking of changing to ethylene glycol (probably a Dow product) as I have eliminated the possibility of going to a boilermate. I plan on doing a drain, flush and fill with distilled water several times to eliminate all trace of the propylene glcol. Does anyone see any issues with converting a previously used propylene glycol system ethylene glycol?

My motivation is EG is a slightly better heat transfer fluid, slightly lower viscosity, less expensive, easier to maintain and less prone for the micro leakage with ProPress fittings. I figured I can clean up most of the visible green corrosion and it may be less likely to return.

Any experience, opinions or comments on things I not thinking about would be very appreciated. Thanks.

Scott

hot_rod

You can blend the two types without a problem, other than unknown toxicity. EG has a higher mammalian toxicity. How's that for a big word!

Best to flush well, dispose of the old, start fresh.

I think the EG would be more leak prone with it's lower viscosity??

I'm not sure the juice is worth the squeeze?

If you go with EG, make sure it is a glycol intended for hydronics.

I'd also label the system well with permanent labels so the next person working on it is aware of the fluid.

Get labels made at a sign shop and have them laminated in clear plastic.

Homeowner96

I should add...domestic baseboard and in-floor radiant heating system. Copper piping with steel tube fin baseboard (1950's single zone construction with huge cast iron boiler, converted to multizone system you see pictured) along with two in-floor zones using PEX.

kcopp

If you are doing the expansion around your place why not bring all the outside piping in or at least insulate them so you don't need the glycol.
If you must go the EG route you will have to separate the water supply out w/ a RPZ type backflow device.

Homeowner96

Ahh. Excellent catch on the backflow preventer. While I can leave the makeup valve closed most of the time, that Honeywell BP900 is a double check vacuum breaker and wouldn't meet code...not something I considered. Thank you.

I also plan to install a flow switch in the short boiler loop and tie that back into the gas valve circuit. The low water cutoff is important but if the main boiler circulating pump stops, there will be a lot of noise and bad things happening before I lose enough water/glycol for the low water cutoff to trip.
Scott

hot_rod

On glycol systems I would not have it connected to t fill. Consider a glycol fill package like the Axiom.

Does that boiler ever short cycle? 8 zones on a copper tube boiler sometimes leads to frequent on/ off cycles.

Homeowner96

No, I have never had a problem with it short cycling - in fact the boiler rarely cycles separately from the zones except for the one in-floor zone. 160k max input BTU, about 2000 sq ft home (1955 brick home and not extremely well insulated either). I think the large 1-1/2" C loop provides a decent thermal mass and having individual zone pumps along with the close-coupled boiler loop keeps the flow rate through the boiler high enough to prevent the short cycling. In addition, the Laars Mini-Therm boiler puts out higher BTUs (close to max BTUs) when the boiler temp is significantly less than the cutoff temp but then regulates the burners back as the temperature comes closer to the cutoff temp (I think I have the cutoff set to 180 or 190 deg F at the boiler). I assumed it was designed this way to reduce short cycling. I think the boiler is also sized about right for the home - a larger BTU ouput would probably want to short-cycle more - I assume. I'll look into the Axiom product though. Thanks.
Scott

RobG

If you have a 160K boiler in a 2000 square foot home you must live in Antarctica. That is 80 BTU's per square foot!

Homeowner96

It get cold here in Michigan and like I said, older home with "50's" vintage insulation

Actually, one of the in-floor loops is an unheated garage that gets turned on occasionally in the winter when one of the cars needs some work so the added capacity is very welcome then as I have to heat a sub-zero slab of concrete. I was worried that the boiler would short cycle for normal house use but as mentioned earlier, this Mini-Therm regulates the burners down quite a bit as you start approaching the cutoff temperature and I really haven't experienced any short cycling.

Short Story:
You should have seen the original 1950's vintage American Standard cast iron oil-fired hot water boiler with a natural gas conversion burner...it looked liked the olympic torch inside that thing when it fired (and made a nice rumble when you laid on the family room floor above). I'm on our local volunteer fire department and I went on a run that was reported as a basement fire. I went in the basement only to discover the same type of set up I had at my home...an old cast iron oil-fired hot water bolier with a gas conversion burner that somehow failed and blew up the cast iron boiler (must have filled the bolier cavity with gas and ignited it). It blew out all the basement windows and took the basement dorr off the hinges and looked like it lifted the house off the foundation for an instant as there were signs of that. The piping, pump, etc. was a twisted manged mess. It was then that I decided to upgrade. I got my boiler for free so couldn't complain and decided to make it work. My old boiler had a 150K BTU input so I figured I could make the copper tube fin Mini-Therm work even though it was more efficient and might be a bit oversized. Sometimes you have to compromise a bit on a retrofit with some free equipment. It's worked out suprisingly well.

tjorn

When using glycol which I would advise that you do make sure the glycol is either premixed with DI water or you have very good quality water to mix it with or you will have issues. 6 grains or less is considered " good water"