Freezing temperatures reduce battery output and stress seals—two reasons ordinary gear can fail outside. This guide explains how to specify cold‑weather emergency lights that maintain the full 90‑minute runtime in winter climates and freezers, including battery chemistry, internal heaters, remote‑head design, and installation best practices. For a broad primer on ratings and use‑cases, see the Wet‑Location Emergency Egress Guide.
Last updated: October 2025
Why cold‑weather units are different
Battery capacity drops as temperatures fall; plastics harden; gaskets lose elasticity. A standard wet‑location light that performs at 70°F can fail well before 90 minutes in sub‑zero conditions. Cold‑weather emergency lights pair wet‑rated enclosures (NEMA 4/4X or IP65/66) with low‑temperature battery solutions and, when needed, internal heaters to stabilize battery chemistry.
Battery chemistry 101 at low temps
- Ni‑Cd (Nickel‑Cadmium): Robust, tolerates cold well, predictable discharge. Common in outdoor egress lights; moderate energy density.
- SLA (Sealed Lead‑Acid): Budget‑friendly, but significant capacity loss below freezing; usually needs a heater in very cold sites.
- Ni‑MH (Nickel‑Metal Hydride): Higher capacity than Ni‑Cd; cold performance varies by pack design; verify the minimum operating temperature.
- LiFePO₄ (Lithium Iron Phosphate): Excellent cycle life and cold discharge; charging below ~32°F must be managed—many units integrate warm‑charge logic or heaters.
Tip: If you’re choosing models from scratch, pair this section with the Wet‑Location Emergency Lights Buyer’s Guide to align chemistry with site conditions.
Low‑temp packs vs. internal heaters
- Low‑temperature battery packs: Purpose‑built cells maintain capacity at lower ambients (e.g., ‑20°F). Simple and efficient where temperatures are cold but not extreme.
- Internal battery heaters: Thermostatically controlled pads keep the battery near its optimal temperature. Best for deep‑freeze applications or sites with prolonged sub‑zero exposure.
- Power considerations: Heaters draw standby power; ensure branch capacity and follow wiring instructions. Heaters typically require continuous AC to pre‑warm packs.
- Labeling: Always verify the fixture’s listed minimum ambient rating with the chosen option installed (e.g., “Rated to ‑40°F with heater kit”).
Remote‑head strategy for extreme cold
When temperatures are too low for on‑board batteries, keep the battery/charger indoors (conditioned space) and power wet‑rated remote heads outside. This preserves runtime and simplifies service access. For trade‑offs and wiring guidance, see Remote Heads vs Integrated (Outdoors).
Sizing: runtime, wattage & spacing in the cold
- Runtime margin: Cold reduces effective capacity; choose a higher‑wattage pack or derate per manufacturer tables.
- Head count & optics: Wider optics and overlapping beams help maintain floor illumination when output sags late in discharge.
- Remote loads: Keep total head wattage within the remote‑capable unit’s allowance; manage voltage‑drop with larger conductors and shorter runs.
- Field verification: Aim and measure near end‑of‑runtime during cold conditions—not just at start‑of‑test on a warm day.
Installation & condensation control
- Seals: Use liquid‑tight hubs; torque lens screws evenly to preserve gasket compression.
- Orientation: Mount per label so drains/weep holes face down; avoid upward‑facing seams.
- Thermal cycling: In freezers, allow full battery pre‑charge and heater warm‑up before testing; avoid propping doors open during tests (condensation spike).
- Service access: Keep indicators visible from a warm corridor when possible; consider remote test switches.
Quick selection table
| Environment | Recommended Approach | Notes |
|---|---|---|
| Mild winter (down to ~0–10°F) | Wet‑rated integrated unit with low‑temp pack | Verify listed minimum ambient; use self‑diagnostics |
| Severe winter (‑20 to ‑40°F) | Integrated unit with internal heater or remote‑head system | Confirm heater power; consider indoor battery + remote heads |
| Walk‑in freezer / cold storage | Indoor battery unit feeding wet‑rated remote heads | Minimize voltage‑drop; keep service access warm |
AHJ checklist
- UL 924 listed; marked “Suitable for Wet Locations.”
- Enclosure rating matches conditions (NEMA 4/4X or IP65/66).
- Listed minimum ambient (with low‑temp/heater option) meets site temperature.
- Remote load and conductor sizing documented; voltage‑drop within guidance.
- End‑of‑runtime illumination verified during cold conditions; test records available.
FAQ
Do I always need a heater for outdoor units?
No. Many low‑temperature packs perform well near 0°F. Heaters are recommended for prolonged sub‑zero exposure or deep‑freeze spaces.
Why did my unit pass a summer test but fail during winter?
Battery capacity and LED output decline in the cold. Size with margin, verify winter runtime, and consider indoor battery with remote heads.
Can a combo unit handle severe cold?
Yes, if listed for the temperature with a low‑temp pack or heater. Verify that the shared battery supports both the EXIT legend and lamp heads for 90 minutes.