Wet vs. Dry vs. Preaction Sprinklers: 5 Differences That Affect Inspection
The Fire Code Authority · Updated November 11, 2026
All three systems put water on a fire, but they hold and release it differently, so they’re inspected differently.
The differences
- 1. What’s in the pipe: wet systems hold water; dry systems hold pressurized air or nitrogen; preaction systems typically hold air and need a detection signal to release water.
- 2. Where they’re used: wet systems in heated spaces; dry systems where pipes could freeze; preaction where accidental discharge is a major concern, such as data rooms.
- 3. Extra components: dry and preaction systems add valves, air supply, and (for preaction) detection and release controls that all need testing.
- 4. Trip testing: dry and preaction valves have trip tests that wet systems don’t.
- 5. Drainage: dry and preaction systems need low points drained to prevent freezing and corrosion.
Important
Inspection frequencies depend on the edition of the standard your Authority Having Jurisdiction (AHJ) has adopted, plus any local amendments and insurer requirements. Confirm with your AHJ or a licensed contractor.
Educational summary, not legal advice or an engineering determination. Confirm requirements with your Authority Having Jurisdiction.