Winterizing Your Sprinkler System: NFPA 25 Field Guide

A sprinkler system's quietest enemy isn't fire — it's freezing. Once piping freezes, the path to rupture is almost deterministic, and the leak usually happens in places no one can reach. In cold regions of Turkey, this is the single biggest maintenance issue for sprinkler systems. NFPA 25 Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems lays out a clear pre-winter roadmap, complemented here with practical notes from field work.

Where Does Freezing Happen?

First, know the operating temperature. A wet pipe system carries water constantly; risk starts below 4°C (40°F), freezing starts at 0°C. Typical risk zones:

• Ground-floor entrance lobbies, cold storage rooms: Prolonged steady cold.
• Attic / ceiling voids: Especially in regions where night temperatures drop to -10°C.
• Enclosed parking garages and loading docks: Air exchange through exterior openings.
• Pipe runs within exterior walls: Pipes crossing un-insulated walls.
• Outdoor valves: Control valves and test drains often left exposed.

Solution 1: Dry Pipe System

Dry pipe holds pressurized air in the pipes under normal conditions; when a sprinkler activates, air escapes, the dry pipe valve opens, and water flows. It's the standard choice for spaces exposed to low temperatures (parking garages, ramps, cold storage). But it has a significant handicap: water reaches the sprinklers with a delay. NFPA 13-2025 (8.2.4.2) requires initial water to discharge from the fully opened test connection in no more than 60 seconds. To offset this delay, NFPA 13 (19.2.3.2.6) increases the design area by 30% for dry pipe systems.

Solution 2: Antifreeze System

For small areas (up to 50-60 sprinklers), an antifreeze-filled branch can be used. Since the 2013 edition, NFPA 13 has allowed only antifreeze solutions listed for sprinkler use in new systems, and the 2025 edition keeps the rule (8.6.2.1). The only exception is premixed propylene glycol used with ESFR sprinklers listed for that specific application (8.6.2.2). NFPA 25 requires annual concentration testing — something often skipped in the field.

Solution 3: Pipe Insulation and Heat Tracing

In enclosed but unheated spaces (parking entry, loading dock), heat tracing cable plus insulation is applied to piping. Self-regulating electric heating cable senses pipe temperature and heats as needed. NFPA 13-2025 permits this (16.4.1.4) with two conditions: (1) the heat tracing system must be listed, and specifically listed for branch lines where used on branch lines; (2) electrical supervision must give positive confirmation that the circuit is energized. Heat tracing also cannot replace a heated valve enclosure for the valve and supply pipe (8.1.4).

NFPA 25 Pre-Winter Checklist

1. Dry system check: Inspect low-point drains, drain accumulated water.
2. Dry valve trip test: Verify air pressure + perform partial/full trip test.
3. Antifreeze concentration test: Refractometer sample from every antifreeze system.
4. Temperature sensors: Install min-max thermometers in risk zones.
5. Insulation check: Is the pipe insulation damaged?
6. Fire department connection (FDC) and control valves: Unobstructed at ground level, cleared of snow and ice.
7. Water tank heating: Heater and thermostat check for outdoor tanks.
8. Backflow preventer: Outdoor units are among the most freeze-vulnerable points.

Common Mistakes in Turkey

Mistake 1: "It doesn't freeze in my region" fallacy

Even mild-climate cities saw multiple nights down to -5°C in December. Companies leaving project garages in mild coastal regions as wet systems faced pipe ruptures the following winter. Do not rely on the comfort of “it doesn't freeze here”.

Mistake 2: Using automotive antifreeze

Car antifreeze (ethylene glycol) does not belong in a sprinkler system: NFPA 13 permits only antifreeze solutions listed for sprinkler use in new systems (8.6.2.1), and automotive antifreeze has no such listing and is toxic. Use an antifreeze solution listed for sprinkler systems instead.

Mistake 3: Forgetting auxiliary drains

Dry system drain points not marked or forgotten during maintenance let water accumulate. Ice formation bulges and cracks the pipe. NFPA 25-2026 (13.4.5.3.3) requires auxiliary drains in dry pipe systems to be drained after each system operation, toward the beginning of the heating season prior to the onset of freezing conditions, and thereafter as needed.

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Conclusion

Winterization is the least glamorous but most impactful maintenance work in a sprinkler system's life cycle. A 100-meter branch damaged by one night of freezing can be drained and replaced — but during that time, the building's fire protection is compromised. The engineer's and operator's job is to prepare the system before winter arrives.