At what temperature do commercial fire sprinkler pipes freeze?

NFPA 13 requires freeze protection for any portion of a sprinkler system where temperatures cannot be reliably maintained at or above 40°F (4°C). Water in the pipes can begin to freeze at 32°F, but NFPA sets the protection threshold at 40°F to provide a safety margin. In Denver, average January lows are around 19°F, making this a real and recurring risk for any unheated or under-heated building zones.

Does Colorado law require commercial fire sprinkler winterization?

Yes. Colorado adopts NFPA 25 as the governing standard for inspection, testing, and maintenance of water-based fire protection systems. Denver incorporates these requirements directly into the Denver Fire Code. Building owners are responsible for compliance, which includes pre-winter inspections and cold-weather maintenance tasks such as draining low-point drains on dry pipe systems and verifying heat in all pipe zones.

Can I use antifreeze to protect a wet pipe sprinkler system in a cold zone?

In some cases, yes. NFPA 13 permits antifreeze loops for short runs through unheated spaces, but the antifreeze solution must be a listed product and must be tested annually to confirm it is within the correct concentration range. Using an unlisted solution or the wrong concentration is a code violation and can affect fire suppression performance. Always work with a licensed fire protection contractor for antifreeze system maintenance.

What is the best system type for unheated spaces in a Colorado commercial building?

Dry pipe systems, which hold pressurized air or nitrogen rather than water in the pipes, are the standard choice for unheated warehouses, loading docks, parking garages, and cold storage areas. Pre-action systems offer an additional layer of control and are common in data centers and archive rooms. Both system types need their own cold-weather maintenance, including low-point drain service and valve enclosure heat verification, but they eliminate the standing water that creates freeze risk in wet pipe systems.

What should I do if a sprinkler pipe freezes or bursts?

Call a licensed fire protection contractor immediately. Do not attempt to thaw pipes with an open flame or torch. Shut off water supply to the affected section if your system allows it, contain any water damage, and notify your building occupants of the impairment. Do not return the system to service without a formal inspection and repair by a certified technician. Your local Authority Having Jurisdiction may require a fire watch until the system is restored to full working order.

When should I schedule my pre-winter fire sprinkler inspection in Denver?

Schedule your NFPA 25 annual inspection in September or October. That gives you enough time to identify and correct any deficiencies before Denver's first hard freeze, which can arrive as early as mid-October. Waiting until late November or December means you may be scrambling for emergency repairs during the coldest and busiest season for fire protection contractors.

How to Protect Your Commercial Fire Sprinkler System From Freezing This Colorado Winter

Sep 26, 2026

TL;DR: Denver winters routinely push overnight lows well below freezing, putting wet pipe fire sprinkler systems at serious risk of burst pipes and system failure. This step-by-step guide walks Front Range facility managers through a pre-season winterization checklist, the NFPA code requirements that apply, and the most common mistakes that lead to expensive emergency repairs.

If you manage a commercial building in Denver, Aurora, Lakewood, or anywhere along Colorado’s Front Range, your fire sprinkler system faces a real and recurring threat every winter. Nearly every night in Denver during January is below freezing, and the thermometer dips to 0°F or lower on an average of two nights. Denver has freezing temperatures more frequently than other metropolitan areas its size, with nighttime lows dropping to 32°F or less in all but three months of the year.

That climate reality has direct consequences for your fire protection system. When the water in a wet pipe fire sprinkler system freezes, it typically expands 10% or more, which can cause blockages in the pipe and, in some instances, cause pipes to crack or burst. A burst pipe does not just mean water damage. It means your fire suppression system is offline until repaired, and your building may be placed under a fire watch requirement until it is back in service.

The good news: freeze damage is almost entirely preventable when you take the right steps before temperatures drop. Here is a practical, code-grounded guide to winterizing your commercial fire sprinkler system.

Why Colorado Commercial Buildings Are Especially Vulnerable

Most commercial fire sprinkler systems rely on water-filled piping that remains pressurized at all times. When temperatures drop below 32°F, any water trapped in exposed or poorly protected pipes can freeze. Many facility managers assume a heated building eliminates this risk, but that assumption is wrong.

Areas most vulnerable include unheated or underheated rooms, attics, crawl spaces, exterior walls, loading docks, and other spaces where cold air can penetrate. In Colorado, the mountain sun can warm the air considerably during the day, but in the evening temperatures quickly drop below freezing, and cold spells from Canada can be intense and accompanied by blizzard blasts. That dramatic day-night temperature swing is particularly dangerous for piping that runs through exterior walls or unheated service areas.

Frozen components can also trigger false alarms or accidental system activations, leading to unnecessary disruptions and emergency service calls. That makes freeze protection both a life-safety priority and a business continuity issue.

What Colorado Code Requires

Colorado does not leave sprinkler inspection standards up to individual property owners. The state adopts NFPA 25 as the governing standard for inspection, testing, and maintenance of water-based fire protection systems. Denver goes further by incorporating these requirements directly into the Denver Fire Code, which means local enforcement is active and consistent.

NFPA 13 Section 16.4.1 states that where any portion of a system is subject to freezing and temperatures cannot be reliably maintained at or above 40°F (4°C), the system shall be installed as a dry pipe or preaction system. If you have a wet pipe system in a space that cannot be kept above 40°F, you have options, but you must address the condition. Ignoring it is a code violation and an insurance liability.

All installed fire sprinkler systems require service, maintenance, tests, and inspections performed to ensure the system will be readily available for operation in an emergency, according to Denver Fire Codes, Federal and State Regulations, NFPA Standards and Codes, OSHA, and insurance company requirements.

Step-by-Step: How to Winterize Your Commercial Fire Sprinkler System

Follow these steps before the first hard freeze of the season. In Denver, that window is typically October through early November, but Arctic fronts can arrive without much warning.

Walk the Entire System and Map All Vulnerable Zones

Start with a building-wide walkthrough focused specifically on pipe exposure. Pay particular attention to piping in attics, entries, penthouses, stairways, under-floor areas, above ceilings, shipping areas, and similar out-of-the-way areas where low temperatures might occur. Document every location where piping is adjacent to an exterior wall, passes through an unheated space, or is near a door or loading dock that opens to outside air. This map becomes your winterization checklist.
Verify Building Heat Is Adequate in All Pipe Zones

Provide heating of adequate capacity to maintain the temperature of no less than 40°F near sprinkler piping. Check thermostat settings in mechanical rooms, stairwells, storage areas, and any other space that may not be on the main HVAC zone. Adequate heat should be provided to all affected areas by extension of the existing heating system rather than other means such as space heaters or other localized heating appliances. Space heaters are unreliable, create fire hazards of their own, and are not a code-acceptable primary solution.
Inspect and Upgrade Pipe Insulation

Any exposed piping should be well-insulated. Check that pipe insulation in attics, crawl spaces, and exterior chases is intact, dry, and rated for the temperatures your building experiences. Wet or compressed insulation loses most of its protective value. Wet sprinkler piping freeze protection is vital, and fire inspectors must visually inspect all sprinkler system piping insulation before sheet rock or any other covering is installed. For existing buildings, that means accessing and inspecting concealed runs before winter arrives.
Test Antifreeze Loop Concentration (If Applicable)

Some wet pipe systems use antifreeze loops to protect short runs through unheated spaces. NFPA 13D requires that antifreeze solutions be tested annually, with samples collected by draining the system or from ports at the top and bottom of the system. There are strict regulations on acceptable antifreeze solutions that can be employed in fire sprinkler systems, so consult with a certified professional when implementing this approach. Using the wrong concentration or an unlisted solution puts you out of compliance and can actually reduce fire suppression effectiveness.
Service Your Dry Pipe and Pre-Action System Components

If part of your building uses a dry pipe or pre-action system, those components need specific cold-weather attention. Building owner requirements under NFPA 25 include draining all low-point drains annually, with extra care required following full flood testing of dry-pipe systems. Examine priming water levels in dry-pipe valves and verify adequate heat for the dry pipe valve enclosure and all areas containing water-filled piping, with a minimum of 40°F maintained. Air compressors and air compressor tanks should be maintained in accordance with manufacturer instructions, and any heat tracing equipment should be inspected according to manufacturer instructions.

For buildings with pre-action systems protecting sensitive areas such as data centers or server rooms, proper winterization is especially critical. See our guide on fire suppression systems for data centers to understand how pre-action systems work and what their maintenance requirements include.
Inspect Heat Trace Systems

NFPA 13 (2019) permits the use of energy-efficient electric heat trace with an insulated and weatherproof jacket so that the sprinkler pipe is maintained at or above the required 40°F. If your building uses listed heat trace as a freeze protection method, test the entire system before winter. Check circuit continuity, thermostat setpoints, and weatherproof jacket integrity at every run. A failed heat trace cable provides zero protection when temperatures plummet.
Seal Drafts and Air Leaks Near Piping

Preventing frozen sprinkler pipes starts with proactive maintenance, and proper insulation, consistent building heating, and sealing drafts near pipes are essential. Focus on penetrations where pipes pass through exterior walls, gaps around loading dock doors, and any HVAC air intake or exhaust that directs cold air toward piping. A can of foam sealant used in the right spots costs almost nothing compared to a burst pipe repair.
Schedule a Pre-Winter NFPA 25 Inspection

A cold-weather inspection must be conducted before the cold-weather season arrives, ensuring that there are no areas with insufficient heat and that physical features and precautions are in place to ensure that sprinkler systems are not exposed to freezing temperatures. Annual inspections are mandated by NFPA 25 across Colorado fire codes, including the Denver Fire Code. Scheduling your annual inspection in September or October means any deficiencies are caught and corrected before the season’s first hard freeze rather than after one.
Set Up Monitoring and an Emergency Response Plan

Temperature sensors and system monitoring help detect freeze risks early, before damage occurs. Make sure your building management system has low-temperature alarms set for any zone containing sprinkler piping. Have employees stay alert for and report potential or existing cold-weather problems, and check fire protection systems more frequently than normal during cold weather. Know in advance which licensed fire protection contractor you will call for 24/7 emergency response if a pipe does freeze or burst.

Is Your System the Right Type for Colorado’s Climate?

Sometimes the most cost-effective freeze protection strategy is converting a wet pipe system to a dry pipe or pre-action system in problem zones rather than continually fighting heat loss battles every winter. Alternative freeze protection options include converting to a dry or pre-action system, or using listed heat tracing.

Dry pipe systems, which are filled with pressurized air or nitrogen rather than water, are used where freezing is a concern and are common in unheated warehouses, parking garages, loading docks, and cold storage facilities. If you are weighing whether your building needs a wet or dry pipe design, our guide on wet pipe vs. dry pipe sprinkler systems for Colorado buildings walks through the tradeoffs in detail.

Common Mistakes That Lead to Freeze Damage

Ignoring unheated maintenance rooms. Wet sprinkler systems may be common in buildings with unheated maintenance closets or equipment rooms. Building owners can open vents or doors to make sure that warm air is moving into these spaces to keep pipes from freezing.
Skipping low-point drain service on dry systems. The air in dry pipes contains moisture, which can condense in the low points of the pipes and freeze. Draining these low points is an NFPA 25 requirement, not optional maintenance.
Using open flame to thaw frozen pipes. Do not use torches or other open flame devices to thaw pipes or other equipment. Open flame near pressurized piping and a sprinkler system is an obvious fire hazard and can damage fittings.
Returning a frozen system to service without inspection. Frozen systems should never be returned to service without proper inspection, repair, and testing. A frozen sprinkler system is more than a maintenance problem, it is an operational and compliance risk.
Relying on temporary or portable heating. Portable fuel-burning heaters introduce carbon monoxide risks and fire hazards. They can also give a false sense of security when they run out of fuel or tip over overnight.
Assuming the system type determines freeze risk for dry systems. Dry fire sprinkler systems can freeze if exposed to sub-32-degree temperatures, and condensation can collect over time and damage the pipes, especially during winter. Do not skip dry system winterization just because there is no standing water in the main piping.

What Happens If You Skip Winterization

Failure to adhere to NFPA 25 requirements can increase the possibility of inadvertently flooding the system with water and causing system freeze-ups, cracked fittings, and water damage. This not only causes expenses for repair and costly downtime, but also severely impairs the effectiveness of your system, putting both occupants and contents at risk.

The local Authority Having Jurisdiction may require a fire watch until the system is placed back into proper working order. Depending on the size of your building, a fire watch can cost thousands of dollars per night in staffing, on top of emergency repair costs.

How Pre Action Fire, Inc. Can Help

Pre Action Fire, Inc. has been serving commercial property owners, facility managers, and building engineers across the Denver metro and Front Range since 2009. Our NICET-certified technicians perform NFPA 25 compliant inspections and winterization services for all types of commercial fire sprinkler systems, including wet pipe, dry pipe, and pre-action configurations. We are licensed by the Colorado State Fire Marshal and offer same-day service when your situation cannot wait.

If you manage a warehouse in Commerce City, an office building in Centennial, a retail center in Lakewood, or any other commercial property anywhere from Broomfield to Parker, our team is ready to help you get your system winter-ready before the next Arctic front rolls in. Contact Pre Action Fire, Inc. to schedule your pre-winter inspection.

For a better understanding of how your fire protection monitoring connects to emergency response when a system event does occur, see our overview of how commercial fire alarm monitoring works.

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