propylene glycol

100% propylene glycol does not conduct heat very well, conversely water is an excellent conductor. The propylene glycol is only added to widen the range of physical change to the water (boiling point/freezing point) and to decrease the corrosiveness of water at high temp. A few things to consider: 1. What is the maximum/minimum temperature the fluid will be exposed to? At higher temps (heater coil)you are more prone to corrosion damage. Lower temps (ambient winter) will allow freezing or increased viscosity of the fluid. 2. What is the maximum/minimum pH the system is designed to operate in. (your choice of propylene glycol product will depend alot on pH tolerance. 3. What is the manufacturers recommendation? (maybe this should have been first) The propylene glycol should only act as an antifreeze & anti corrosion agent in your system around the heating coil since your use for in floor heating should not reach more than 212 Deg F (100Deg C) through out the system. Hope this helps.

Questioning why you would want to add an anti-freeze to a home heating system unless this is a summer home and you winter in Florida. Even if that was the case you would have to maintain the temperature above freezing or the other plumbing would freeze. Propylene glycol is just another poison in your home to worry about.

RV anti-freeze that I know about is for the drinking water system is grain alcohol. Would not recommend it.

The mfg. only specifies "propylene glycol" due to it's non-toxic nature. I live in Up-state NY (Buffalo) and we have frequent power outages thus the need for anti-freeze protection. The system runs @ 105deg max and @ 25psi max.

50/50 should be your best bet. just make sure all components are compatible with the pH level of the mixture. The pH will be on the bottle. you can check the health of your system by periodically checking the fluid pH with test strips...here's the link. http://www.indigo.com/test-strips/pH-test-strips.html When pH falls off 35-35% it's time to either add conditioner or replace fluid. Again, hope this helps

It sounds like the mfgr's recommendation is 25%, so 30% is likely close enough. Propylene glycol is much safer than ehtylene glycol, in fact, it's used as a moisturizer in some cosmetics. But do be sure your system is absolutely leak-free above your expected operating pressure and temperature! In-floor radiant heat works OK, but leaks are (as I'm sure you know) disastrous!

You can get the "pink stuff" house branded RV anti-freeze at Wal-mart for around $3.50/gal. The Prestone pink stuff is about $6.00/gal. We use it for our travel trailer (caravan for the folks on the other side of the pond) and to winterize the engine on our bowrider. It is safe for potable water systems and you can probably drink it (although not recommended). You may find that you will get good freeze protection at fairly low concentrations, assuming the interior of your house is not going to get as cold as it does outside on a clear winter night in Buffalo.

You might also want to look at Dowtherm and similar heat-transfer liquids for better long term results.

Maybe, but don't forget whether it's safe enough in the event (almost certain) of a leak! Wouldn't want to jeopardize the family or the water table...

Thank you all for your input. I will be using "peak"rv antifreeze. it is a 27% to water solution giving it a rating of -50deg. my next problem is the ratio of this to distilled water to get to the 25%glycol to 75% water ratio specified by mfg. ( they were only able to tell me it's ok to use this product as opposed to the 100% solution they normally use in commercial applications.)

If what you need is a 25% solution in water, and what you have is a 27% solution in water, that's probably close enough. If what they "normally" use is 100% but they say lesser strength is acceptable, I think I'd leave it at that.

If it's more complicated than I seem to think it is, obviously you should ignore me...

One other consideration is the viscosity of the resulting solution. Propylene glycol significantly increases this viscosity at higher concentrations. This will decrease pump output. The recommendation for a 25% concentration seems wise. But, if you look at a table of freezing point depression for various concentrations of the glycol, it is possible that you could select a lower concentration and thus increase the heat transfer capability of the system.

--JMM