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Glycol (aka, antifreeze) Right for your system?


Bob "Hot Rod" Rohr
July 16, 2009
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Here are some tips and ideas for the use of antifreeze solutions in your heating system"

First,when is it required? Certainly any system installed in an outdoorsetting and in a freezing climate is a perfect candidate. Snowmeltsystems, no doubt. Remote cabins in the mountains, yes. Possibly a homethat is vacant for extended periods during freezing conditions.

I don't believe glycol is required in every hydronic system. It does require some extra time, money, and maintenance.

Glycolactually comes from crude oil. The refiners put it through several"cracking" process to produce the solution we call glycol.

There are two main types of glycol common to heating and cooling use. Propylene glycol (PG), and ethylene glycol (EG).

Propyleneglycol is considered non toxic, or at least the FDA labels it atlow-acute oral toxicity. In a food grade form, PG is actually common inthe food industry as a flavor- and scent-enhancer. Look at the labelson stored bakery goods to see PG or some variety used.

Beinglow-acute, or non-toxic, PG can be used safely in systems wheredomestic water could come in contact with the fluid, or where errantspills would not cause serious problems.

EG is still used,and common in larger commercial and industrial applications. It isgenerally less expensive and less viscous, which means it's cheaper andbetter at moving heat. EG is considered to have moderate-acute oraltoxicity compared to PG's low rating. It is not FDA or USDA approvedfor use in the food industry.

EG can kill pets if ingested, and it's not a pretty death. Pets are attracted to the sweetsmell and taste. Handle and dispose of these fluids (like automotiveantifreeze) carefully. Most oil-change stores will dispose of drainedantifreezes for you at little or no charge. They do recycle thesefluids.

If you come across a system with an unknownglycol, the two types can be blended. However you end up with anunknown toxicity concoction. I'd rather the old fluid be flushed anddisposed of and start fresh.

A few tips should you decide to glycol your system:

First,run a cleaner through the system. I prefer a good hydronic-specificcleaner. Dow suggests a 1-2% solution of TSP. I've had one suppliertell me that automatic dishwasher detergent can be used as it doesn'tsuds up and it cuts grease and oil well. All these products arebasically strong soaps. Be sure any cleaners are completely flushed outbefore you add the glycol.

Next, be sure the system isfree of any leaks. Glycol has a sneaky way of finding the smallest ofleak paths. Threaded joints, packing around valve stems, etc. Plan onseeing some green "fuzzys" at some locations.

Third,select a quality brand and blend it carefully. Glycols should only beblended with filtered DI (deionized) or DM (demineralized) water.Plain tap water may or may not be good to blend with. Hydronic glycolshave inhibitor chemicals added. These ingredients help buffer the pH,lock up hardness, scavenge oxygen, etc. If you blend with water of aquestionable quality, you will compromise these important components ofthe glycol right off the bat.

I'd suggest purchasing pre-blended hydronic glycols. Most of the hydronic antifreezes areavailable in anywhere from a five-gallon bucket to a rail-car quantity,pre-blended. Beware of the freeze protection and the burst temperatureson the container label.

Stick with the brand names toassure it is first-quality and properly inhibited. If your systemcontains any aluminum components you MUST use a special AL (aluminum)blend. All of the major hydronic glycol manufacturers offer AL fluidsnow. Several manufacturers also offer HD (heavy duty) products. Thesehave a better inhibitor package, I suggest HD fluids for solarapplications as they handle over heating better, or longer :)

Iwould highly recommend any boiler "auto fill' systems be disconnectedfrom a system with glycol installed. You can buy, or build a glycolfill tank to assure the system maintains pressure. Most of the newermodulating-condensing boilers require 10-12 psig to fire off. A glycolfill system will assure the system does not lockout due to low-pressureconditions. It is quite possible for a hydronic system to burp a littleair as the heating season begins so be sure you cover that loss ofpressure to prevent nuisance call backs.

Last, invest inglycol testers to maintain your systems. Buy at least a freezeprotection tester, such as a refractometer. Buy a good that will giveyou years of service. Also, get a pH tester because this will give youthe first sign that the fluid has been compromised. I like the smallpocket-sized electronic style of tester.

Label all thesystems where you install glycol! this can be as simple as a magicmarker note on the boiler jacket. Many of the glycol suppliers havepre-printed labels for this purpose. Define the type of fluid and thepercentage of mix, along with your company name and contact numbers.

Checkthe systems yearly for pH and protection level. if the glycol has beenoverheated it may be salvageable with an inhibitor boost kit ifdetermined soon enough.

Most glycol manufacturer offer a more in depth analysis if you mail them a sample.

A few last tips...

Glycolingadds cost to the system. Be sure to add to your price for theadditional components and labor hours. An extra day's labor is notuncommon for the cleaning, flushing, filling, re-purging, testing, anddocumenting the installation.

Check the boiler installation manual. They will indicate a maximum percentage of glycol allowed.

Pumps may need to be up-sized when glycol is used.

Expansion tanks may need to be up-sized.

Tightly seal any unused antifreeze containers to limit to oxygen intake, which can deplete the oxygen scavenger in the fluid.

Disposeof old fluids properly. I use Safety Kleen for pick up of largequantities. They will document the disposal to keep you covered from aliability position.

Never use automotive antifreeze. it contains silicates which WILL sludge your systems. Trust me on this one :)

Forfurther information contact the manufacturers for data sheets andEngineering Guides. Dow has an excellent Engineering and Operatingguide available for PG and EG fluids. as well some software programsfor design use.

(Bob "Hot Rod" Rohr has many years of pratical experience as a contractor.)