I am installing a hydronic root zone heating system.  Can I use methanol ($1.00/gal) instead of propylene glycol ($20.0/gal) for antifreeze?  Will the methonol evaporate when the water mixture hits 100F?

Why do you need any antifreeze at all on the hot side?

It is a 50 gallon closed loop system in a non heated greenhouse using a 30,000 BTU propane water heater to provide the heat.

Three options (in order of preference)

1) Use water and allow the system to drain when not in use. Maybe use air to blow it out if you can't get it to drain.
2) Have backup electric to keep it just warm enough to prevent freezing
3) For only 50 gallons, you could use propylene glycol.

Methanol is toxic in enclosed spaces and a solution of methanol that is freeze-protected down to -40 has a flash point of less than 90F, not to mention the presence of the propane burner.

Try a commercial dairy supply for propylene glycol. I paid just under $12 per gallon when I bought a 55 gallon drum last year. They also sold it in 5 gallon size.

You guys are great!!  I'm still looking for a commercial dairy supplier thats sells prpylene glycol, but I like the idea of just using water and draining the system when not in use.  I have no electrical power, but if the pilot light stays lit on the propane water heater, that should stop any freezing in the system-right?  The lines are buried about 10 inches deep and run for 240 feet.  Will I get enough natural circulation if I keep the water temp at 100F ?

I have no electrical power

Um, NO electrical?

Couldn't you just run an extension cord out to the "garden"? :-)

I am 600 ft from power($1800 quote from the power company).  I am putting in a 60w solar collector into a 100AH battery to run the pump to circulate the water.

Jabsco has a good little 12V pump that is made for pumping hot fluid. Draws about 15W or 1.2A at 12V. At marine stores or on the internet.

You cannot safely drain a radiant heating system. It's also a really poor idea to continually drain and refill a heating system.

if you're using AC power, the new ECM pumps are low draw. the Alpha has a setting that maxes out at 3GPM/3 ft of head and 8w of power. we just finishing designing a radiant system that uses 10w of power in total using that strategy. We never liked any of the DC pumps we've seen, but maybe there are better ones these days.

I heard tell of a guy in California who used vodka as antifreeze. I would stick with propylene glycol, personally.

No one in sunny California would ever use vodka as antifreeze. Methanol maybe, but not vodka.

Many do not understand anti-freeze. The average plumber (and many not-so-average) think that a 50/50 mix is the only recipe. It is not.

First, you have to decide when you need it and why e.g. will the system have to work in design space heating conditions (coldest day of the year)? Or are design conditions really at the shoulder months. Either way the mix should be engineered for "burst" protection in cold months when the system doesn't operate and for "flow" when it must operate in sub-freezing weather. Food grade anti-freeze designed for space heating is the standard for residential space heating.

Cheap alternatives is the SOP for shooting yourself in the foot.

I will trade you Cryotek for good vodka any day!

I guess if you have a still you could make yourself some good antifreeze :0)

-Rosalinda