TL;DR: Dry sprinkler systems keep pipes filled with pressurized air instead of water, so they can protect unheated warehouses, parking garages, loading docks, and attics from freeze damage during Colorado winters. They cost more to install and maintain than wet systems and react slightly slower, but for the right space they are the only code-compliant option.
Every winter, Front Range facility managers deal with the same freeze-related headache: buildings or building sections that cannot stay reliably above 40 degrees Fahrenheit. Loading docks, parking garages, attics, freezer warehouses, and unheated mezzanines all fall into this category. A standard wet pipe sprinkler system is not an option in these spaces because the water inside the pipes can freeze, crack the piping, and cause a system failure right when it is needed most.
That is where dry sprinkler systems come in. This guide explains how they work, what tradeoffs come with them, and when a Denver metro or Front Range property actually needs one.
What Is a Dry Sprinkler System?
In dry pipe systems, the pipes are filled with pressurized air or nitrogen, rather than water.
The water itself is held back at a dry pipe valve, usually located in a heated area of the building.
NFPA stipulates using dry sprinkler systems when the ambient temperature of an area cannot be maintained at or above 40°F (4°C), putting wet systems at risk of breaks and malfunctions due to freezing.
This makes dry systems a common fit for Colorado’s unheated commercial spaces, especially given how far temperatures can drop across the Front Range in winter.
How a Dry Sprinkler System Works
When a fire generates enough heat to open a sprinkler head, the pressurized air or nitrogen in the pipe escapes first.
When the air in the pipe network escapes through an open sprinkler, the water pressure below the valve becomes greater than the air pressure above it, pushing the dry valve’s clapper open and releasing water into the pipes.
The valve mechanism itself is designed to hold back a large amount of water pressure using only a small amount of air pressure.
Dry valves generally operate on a differential principle, for instance if a valve has a 6:1 differential, it only requires 1 psi of air pressure to hold back 6 psi of water pressure.
Because air has to escape before water arrives, dry systems have a brief built-in delay compared to wet systems.
The design of dry sprinkler systems causes a small delay between the time a sprinkler head activates and when water flows onto the fire.
To manage this, many systems use quick-opening devices.
Quick-opening devices speed water delivery in dry sprinkler systems to meet NFPA time limits by accelerating the tripping of dry pipe valves.
Code Requirements for Water Delivery Time
NFPA 13 sets specific limits on how quickly water must reach the most remote sprinkler after a valve trips, though the requirement depends on system size.
There is no required water delivery time where the system volume is limited to 750 gallons, although the volume is permitted to be increased where the water delivery time to the most remote hose connection does not exceed three minutes.
For larger systems, the standard 60-second rule generally applies.
Systems with a capacity of greater than 750 gallons, or greater than 500 gallons without a quick opening device, must deliver water in 60 seconds.
A licensed fire protection contractor calculates and verifies this delivery time during design and acceptance testing, and it gets checked again during periodic trip tests throughout the system’s service life.
Pros of Dry Sprinkler Systems
- Freeze protection. No standing water in the pipes means no risk of freeze-related pipe bursts in unheated or seasonally conditioned spaces.
- Code compliance for unheated areas. Dry systems are often the only NFPA 13 compliant option where temperatures cannot be reliably kept above 40 degrees.
- Flexibility for mixed-use buildings. Dry systems can be zoned to cover just the unheated portion of a building while the rest uses a wet system.
Dry systems can be installed on their own or connected to other types of sprinkler systems.
Cons and Tradeoffs of Dry Sprinkler Systems
- Slower response time. The air-then-water sequence adds seconds compared to a wet system where water is instantly available at the sprinkler head.
- Higher installation and equipment cost. Dry systems require additional control equipment not found in wet systems.
The more complex operation of a dry sprinkler system requires extra control equipment and air pressurization devices not found in wet systems. - Corrosion risk with the wrong pipe material. Steel piping can corrode quickly when combined with pressurized air.
Steel pipes tend to perform poorly in dry systems that rely on pressurized air instead of nitrogen, because oxygen in the pressurized air tends to react with any pools of water trapped in the system and corrode the pipes, sometimes as quickly as two years after installation.
Copper tubing tends to hold up better.
Copper tubing is a popular choice for dry systems because it does not become as brittle at low temperatures and is less susceptible to corrosion. - Installation precision matters. Pipes must be pitched correctly to drain fully, or trapped water can still freeze and cause failures.
NFPA 13 provides direction on how much slope is required for dry pipe installations, one quarter inch per ten linear feet of pipe for mains and one half inch per ten linear feet for branch lines. - More frequent, more involved testing. Dry systems carry additional inspection and testing obligations beyond what wet systems require.
Because of these tradeoffs, the NFPA does not recommend dry systems as a default choice.
The NFPA minces no words in its recommendation to only install dry sprinklers on parts of a property where environmental circumstances make them the best solution.
For a full side-by-side comparison of how dry systems stack up against wet pipe systems, see our wet pipe vs. dry pipe sprinkler system guide.
Testing and Maintenance Requirements Under NFPA 25
Dry systems require more frequent attention than wet systems because the air side of the system needs to be monitored constantly for pressure loss, and the valve mechanism needs periodic trip testing to confirm it still performs as designed.
Typical NFPA 25 obligations include:
- Weekly or monthly gauge checks on air pressure, since a slow leak is often the first sign of a problem
- Quarterly testing of low air pressure alarms and priming water levels.
Low air pressure supervisory devices, if provided on the detection system, shall be tested quarterly in accordance with the manufacturer’s instructions. - An annual partial trip test of the dry pipe valve, with a full-flow trip test required on a longer cycle.
Dry-pipe valves require an annual partial trip test plus a full-flow trip test every 3 years, not an annual full trip, a common point of confusion. - Documentation of trip time, water delivery time, and pressures during full-flow tests, compared against the original acceptance test baseline.
The full-flow test records air and water pressure, trip pressure, trip time, and water-delivery time, compared against the original acceptance-test baseline.
These test results matter over time. As pipes age, delivery times can slow down, which is a sign of internal corrosion or obstruction.
As pipe corrodes and narrows, delivery time increases, and a system that took 45 seconds when new may take 90 seconds today.
When a Colorado Facility Needs a Dry System
Dry sprinkler systems make the most sense for spaces that cannot be reliably heated through a Front Range winter, including:
- Parking garages and loading docks open to outside air
- Unheated warehouses, storage buildings, and distribution centers
- Attics, cocklofts, and unconditioned mechanical spaces
- Freezer and cold storage rooms
- Exterior canopies and covered loading areas attached to a heated building
If your facility is dealing with recurring freeze issues on a wet system, or if you are planning new construction or an addition into unheated space, it is worth having a licensed contractor evaluate whether a dry system, a properly designed freeze protection plan for an existing wet system, or a pre-action system is the right fit. Facilities with sensitive contents like data halls or archive rooms often lean toward a different variation entirely. Our pre-action fire suppression system explainer covers how that option differs from a standard dry system, and our data center fire suppression systems guide goes into more depth for server rooms and similar critical spaces.
Working With a Licensed Colorado Fire Protection Contractor
Dry sprinkler systems are code-compliant and effective, but they only perform as designed when they are engineered, installed, and tested correctly. Pipe slope, pipe material, valve sizing, and quick-opening device selection all affect whether a system meets NFPA 13 water delivery requirements and holds up over years of Colorado winters.
Pre Action Fire, Inc. designs, installs, and maintains dry sprinkler systems for commercial buildings across the Denver metro area and Front Range, and every technician on our team is NICET certified and trained to NFPA 13 and NFPA 25 standards. If you are weighing a dry system against other freeze protection strategies, our guide to protecting a commercial fire sprinkler system from freezing covers additional options worth considering for buildings with only partial exposure to cold.
Recommended Reads
- Wet Pipe vs. Dry Pipe Sprinkler Systems: Choosing the Right Setup for Your Colorado Buildi
- How to Protect Your Commercial Fire Sprinkler System From Freezing This Colorado Winter
- What Is a Pre-Action Fire Suppression System and When Do You Need One?