For Love and Glycol

One of the best opening lines in rock right here…

The Boss, The Big Man and “10th Avenue Freeze Out.”  ’Nuff said!

Speaking of freeze outs, do you glycol your systems?  And since when is “glycol” a verb?

Glycol, of course, is propylene glycol, or heating system anti-freeze.  Should you use it?  How much should you use?  And what are some of the complications?  All good questions – we’ll tackle ‘em one at a time.

First, should you use it?

Easy answer: it depends.

Back when I actually worked for a living, we would “glycol” systems only when the house was going to be vacant for an extended period of time.  We’d winterize homes for a local realtor, and since the houses were for sale and with winter approaching, glycol seemed prudent (along with draining the water pipes and adding glycol to all the traps).

In “normal” situations, we’d rarely glycol a system unless the pipes were exposed to drafts that couldn’t be sealed up.  We weren’t all that worried about power outages – even though it was a reasonably rural area, power outages were infrequent and usually of short duration.

That said, a 30% glycol/70% water solution is pretty cheap insurance.  I’d venture to say that mixture would handle most any situation in the continental US (Alaska, you live by your own set of rules!).

Here are some glycol particulars:

First,  if you’re using concentrated glycol and mixing it in the field, it’s best to mix it with water before you pump it into the system.  I’ve seen situations where guys have pumped in the glycol and then pumped in the water and expected it to mix in the boiler and pipes while the circulator is running.  That’s sorta like using “Powerball” as your retirement planning - it’s optimistic

Second, different concentrations of different brands will give you different protection.

For example, NOBURST -100 says at a 100% concentration you have protection to the following levels:

Freeze Point: -60 degrees
Flow Point: -70 degrees F
Burst Point: -100 degrees F.

They define Freeze Point as the temperature where ice crystals form in the fluid, Flow Point as the temperature where the fluid will still flow, and Burst Point is, well, ka-boom!

I’d say at full power NOBURST -100 would take you through the next Ice Age.

At 40% concentration, you’re covered for flow down to +2 degrees F, and for burst down to -10 degrees F.  For a standard residential application, that’s more than good.

And third, glycol will change the flow and head pressure requirements in a system.

Glycol is heavier and thicker than water, with a lower specific heat value.  What does all that mean?  Well, it goes back to the Universal Hydronics Formula:

GPM = BTUH ÷ (ΔT ×500)

The number we’re concerned about is the 500, which comes from multiplying the weight of 1 gallon of water (8.33 lbs) by the  60 (minutes per hour), by thespecific gravity of water (which is 1) and by the specific heat value of water (also 1).

8.33 × 60 × 1 × 1 = 499.8, or 500

Cryo-tek -100 publishes its weight at 8.78 lbs/gallon, specific gravity at 1.054 and specific heat at .843.  Using this undiluted, you’d change the 500 to the following

8.78 × 60 × 1.054 × .843 = 468

That will increase the GPM required compare to 100% water.  It’ll also increase the head loss through the piping system.  We’ll discuss that, as well as anti-freeze and aluminum heat exchangers, in our next installment.

Till then, I’ll leave with Bruce’s finest, and my #1 song evah!

“The skeleton frames of burned out Chevrolets…”  What a great line!


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