6.1 Antifreeze Systems: Types, Listed Solutions, Backflow Isolation & Testing Procedures
Key Takeaways
NFPA 25 (2023) includes exceptions for acceptable existing factory premix and certain listed ESFR applications.
The existing-solution limits are 30% propylene glycol or 38% glycerin by volume, with the other applicable conditions still required.
For listed solution sampling and refill, follow the manufacturer’s instructions under 5.3.4.2.2.
Unknown or unacceptable solution cannot be approved solely from a cold freeze-point reading.
Identify the solution before judging the system
An antifreeze system is a wet sprinkler arrangement using a solution that remains usable at the expected low temperature. Its inspection involves more than reading a freeze-point scale. The technician must establish the product or acceptable existing formulation, system materials, temperature exposure, sampling requirements, and any conditions governing continued use.
NFPA 25 (2023), 5.3.4, is the controlling exam provision. Earlier transition notices emphasized a September 30, 2022 deadline for listed solutions. The published 2023 edition includes exceptions, so “every unlisted solution is prohibited after 2022” is not an accurate rule for this exam.
Listed solutions and the existing-solution exceptions
Listed antifreeze is the general requirement. Under 5.3.4.4.2, an existing factory-premixed solution may remain where concentration is limited to 30% propylene glycol by volume or 38% glycerin by volume. This is not permission to mix concentrate in the field, add an unknown product, or refill any system with a legacy mixture. Its identity, concentration, freeze protection, and applicability still need to be established.
Under 5.3.4.4.3, a specific application involving ESFR sprinklers listed for use with premixed propylene glycol above 30% has a separate provision. Verify that actual listing rather than generalizing it to ordinary sprinklers. The standard also addresses the use of listed replacement solution outside certain listing limitations while retaining the temperature-range limitation. Read the complete applicable paragraph before deciding whether an existing arrangement can remain.
| Finding | Required reasoning |
|---|---|
| Identified listed product | Apply product instructions and the relevant NFPA 25 provisions |
| Identified existing factory premix within the exception | Verify concentration and adequate freeze protection before accepting continued use |
| Unknown solution | Resolve identity; where it cannot be reliably determined, apply the drain-and-refill requirement |
| Excess legacy concentration | Do not approve from a cold freeze point alone; evaluate whether a specific permitted exception actually applies |
Material compatibility matters
The solution must suit the system materials. CPVC provisions are particularly important: NFPA 25 allows a listed solution or the permitted glycerin arrangement, while specifically prohibiting diethylene, ethylene, and propylene glycols under that provision. Do not infer compatibility from a generic “food grade” description or from the product's broad chemical family. Obtain the actual listed product documentation and pipe manufacturer's requirements.
A product's listing can include occupancy, sprinkler, volume, material, pressure, and temperature limits. The standard's existing-system provisions must be read together with those details. Do not assume all listed products provide the same minimum temperature or that more concentrated fluid is necessarily safer. Fire behavior, viscosity, compatibility, and hydraulic performance matter as well as freezing.
Understand the hydraulic arrangement
Identify the supply connection, isolation valve, check or backflow equipment, expansion arrangement, fill point, and sampling points. Cross-connection protection follows applicable health and plumbing requirements and the approved installation. An RPZ is not a universal answer for every arrangement, and the inspector must not redesign that connection from a generic sketch.
Temperature changes can expand trapped fluid. Check the installed expansion or relief arrangement against its approved design and product instructions. A universal 175 psi relief setting is inappropriate when component ratings or the approved design require something different. Investigate leakage and abnormal pressure without closing or plugging a relief discharge to hide the symptom.
Annual sampling before freezing
Test at the onset of the heating season under 5.3.4. Establish the type of solution from reliable records and testing. The sampling provisions address top and bottom locations and additional remote or supply-interface locations where those are not already represented. For systems over 150 gallons, the provision calls for an additional point for each 100 gallons, subject to the listed-solution manufacturer provision. For listed solutions, follow the manufacturer's specified number of test points and refill procedure under 5.3.4.2.2.
Do not equate “remote” with “highest” in every building. A remote portion can be lower or at an intermediate elevation. Identify actual sampling locations on the system drawing and report. Collect representative samples without uncontrolled withdrawal that draws fresh water into the loop and dilutes it. Record the location and measured result for each sample rather than averaging a warm, diluted sample into a colder acceptable one.
Evaluate and correct failures
Use an instrument and scale calibrated for the actual solution. Compare every result with the applicable concentration or product specification and the temperature required at the protected location. A sufficiently cold reading does not establish that an unknown chemical is acceptable, and an acceptable concentration does not establish adequate freeze protection for every climate.
When a sample has an incorrect freeze point, the standard requires complete draining and refilling with a listed or otherwise acceptable solution under 5.3.4.4. Follow the listed product's refill and flushing instructions. Never improvise a correction by injecting raw concentrate or adding water. Capture removed fluid and arrange disposal through the applicable receiving authority and product requirements.
Example: an existing premix
An existing system has reliable records identifying a factory-premixed 30% propylene glycol solution. Its annual samples meet the applicable concentration and protected-space temperature requirements. It cannot be rejected solely because it lacks a listing and the calendar is after September 2022. Evaluate the 2023 existing-solution exception and all applicable conditions. In contrast, an unknown field mix with a low measured freeze point does not gain that exception just because its reading looks cold enough.
Document solution identity, locations, results, criteria, deficiencies, corrective work, and restored system status. Keep the antifreeze information sign accurate and preserve records for future identification.
Sources checked October 19, 2026: NFPA 25 (2023), 5.3.4; NFPA's 2023 antifreeze fact sheet.
Which statement correctly describes NFPA 25 (2023) existing antifreeze?
Every unlisted solution is prohibited solely because the date is after September 2022
An identified existing factory premix can remain under the specified concentration and other applicable conditions
Any unknown solution is acceptable if it reads below freezing
Field concentrate can be added whenever a sample is weak
For a listed antifreeze solution, what determines its sampling-point and refill procedure under 5.3.4.2.2?
A universal two-point rule with no exceptions
The local practice-bank answer count
The manufacturer’s instructions under the applicable standard
The coldest value from any one sample
Why inspect an antifreeze expansion arrangement?
To introduce fresh water whenever temperature rises
To permit chemicals to return to the potable main
To eliminate all sampling
To accommodate trapped-fluid expansion without exceeding the approved component and system limits
Sections you finish are checked off in the contents.