Fire Sprinkler Antifreeze loop systems

 In Fire Safety

What is an Antifreeze loop (AFL)?

Antifreeze loops protect areas in a building or outside a building that are prone to freezing.  A check valve isolates the anti-freeze loop from the rest of the fire sprinkler system.  There is also a main drain and a fill cup to assist in the draining and refilling of the loop.  AntiFreeze loops are filled with NFPA and Local Ordinance approved antifreeze solutions; either Propylene Glycol (PG) or Glycerin (GL).

AFL, anti-freeze loop

Antifreeze Loop System

 When a system is filled, the solution is pumped in either through the fill cup or drain area.  The solution is then locked into the area going to the protection by the check valve at the bottom of the loop.

How have antifreeze loops been used in the past?

Antifreeze systems where filled with a mixture of either solution and water.  The Field Technician would use a concentrate of the antifreeze solution and mix with water to get to the desired mix rate to produce a freeze point needed for your location.  For Instance, NFPA allowed up to 50% PG and 50% water to be put into a system.  This would give a freeze point between -40°and -60°.  As with any antifreeze solution, the concentration of the solution will break down over time, causing the freeze point to increase closer to +32°.  When the testing point reached below -10 Degrees in the Chicagoland area, the testing company would suggest refilling the system with a new solution.

Propylene Glycol (PG) is the most common solution found in the Chicagoland area.  If your location is in the City of Chicago – Glycerin (GL) is the only solution approved per city code.

What has changed in NFPA codes for Antifreeze Loops and why?

Following reports of a fire incident involving a sprinkler system that contained a high concentration of antifreeze solution, research and standards development activities were begun to address concerns raised by the combustibility of antifreeze solutions in sprinkler systems.  These instances showed that some solutions may have had more PG or GL mixed in the solution that was allowed.  The higher concentration allowed for combustion to incur, fueling the fire and causing catastrophic conditions.

With the 2014 NFPA release of NFPA 25 and NFPA 13 (The rules and guidelines on how to install or inspect Water based Fire Sprinkler Systems) have lowered the percentages allowed  of antifreeze solution and it has to be premixed by the manufacture.  This will ensure that the solution used will not allow a high concentration to be accidentally mixed and cause a combustion.

The two solutions that can be purchased for these systems have the following properties:

Propylene Glycol 38%

Glycerin 48%

Freeze Point


Flow Point



Burst Point



All temps are in Fahrenheit


What does this mean for your building?

If your current solution is Propylene Glycol and test at or higher than +3° or Glycerin testing at or higher than -5°, we will recommend replacing the solution.  If your system has a higher concentration and is testing better than these freeze point (example -20°) than that solution can stay in the system until 2022.  At that point, NFPA mandates any older solution be changed to the approved mixture.  (So if it’s better than what we can put in today – leave it be until 2022).

Depending on the location of your building and how the system can be effected by colder weather and wind chills, You might consider the following options for the Chicagoland area:

  • Use an approved Glycerin solution in the system (a better freeze point).  Costs to recharge an Antifreeze system varies on the size and gallons of the system.  Ranging between $800 – $8000.
  • Convert the system to a Dry Fire Sprinkler System.  This Can cost anywhere from 8K-20K depending on the size).  Comparing the costs of refilling your antifreeze system every few years, this option will allow better protection from freezing if maintained and save costs over the life of the system.
  • If possible, Heat the area in question.  Some systems where designed for a building that required a non-heated area but may not be needed anymore due to mechanical or tenant changed.

Your system tested fine, but you still had a frozen pipe break/burst.  Why?

Depending on who filled your system, and where the tests ports where used can affect the testing of the solution.  We have found that the system should be tested from the loop drain area AND another point further into the system if possible.  Not All systems had a valve installed at the end or middle of the system so the test point may only be from the drain area.

If the solution was not mixed properly, you may have some areas of the solution that might test higher or lower than other areas.  For Instance, when the company filled the system, they may have mixed 20 gallons of solution and pumped into the system.  They then realized they needed one or two more gallons, so they mix another small batch and pumped it in.  Because the piping goes up and down, a higher or lower concentration might be found near the testing point than the rest of the system.

So if the company used a solution that was mixed to -20° throughout the majority of the system, and a solution at -50° to finish pumping it in, then the test point at the drain would be -50° and not -20°.  AS the system breaks down over time, then you might still get a test of -40° at the valve, but the far point of the system might be +5°.   So one benefit of the new premixed solution is that it should be consistent throughout the system.

To See the official NFPA changes go to:


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