When should I use a spring-return actuator vs a non-spring-return?
Safety-Driven Selection
The decision between a spring-return and non-spring-return actuator is primarily a safety and code-compliance decision, not a cost or convenience choice. Spring-return actuators contain a pre-tensioned mechanical spring that drives the actuator to its fail position (fully open or fully closed) when power is interrupted. Non-spring-return actuators simply stop where they are — fail-in-place.
### Where Spring-Return Is Mandatory
Australian building codes, aligned with the International Mechanical Code (IMC) and National Fire Protection Association (NFPA) standards, require spring-return actuators for safety-critical functions:
**Smoke control dampers**: Under UL 555S and AS 1682.2, smoke dampers must fail to their fire-safe position within 75 seconds of a fire alarm signal. Spring-return actuators guarantee this motion without relying on backup power.
**Freeze protection valves**: Outdoor air heating coils in climates where entering air can fall below 0°C require spring-return actuators that fully open the heating valve — not close it — on power loss, preventing coil freeze rupture.
**Stairwell pressurisation dampers**: Per the Building Code of Australia (BCA/NCC), pressurisation systems in fire-isolated stairways must fail open or closed as dictated by the smoke control strategy, and spring-return mechanisms are the accepted means.
### The Energy Argument Has Shifted
Historically, non-spring-return actuators were favoured for energy efficiency because spring-return models had to continuously energise a holding coil to keep the spring compressed — drawing 5–10W in the normal operating position. Modern brushless DC motor technology has largely closed this gap. Belimo's current-generation spring-return actuators consume as little as 0.5W in the holding position, making the energy difference negligible for most applications.
### Practical Selection Rule
For modulating control on non-safety dampers and valves (VAV boxes, cooling-only chilled water valves, return air dampers), non-spring-return actuators are cost-effective and appropriate. For any application where a power failure could create a safety hazard — smoke, freeze, toxic exhaust, pressurisation — specify spring-return and document the fail position clearly on the mechanical schedules.
Spring-Return vs Non-Spring-Return Actuator Selection Matrix
Application-based selection guide with code references for Australian and international HVAC installations.
| Application | Required Type | Fail Position | Code Reference | Typical Torque Range |
|---|---|---|---|---|
| Smoke control damper | Spring-return | Open or closed per strategy | UL 555S / AS 1682.2 | 10–35 N·m |
| Stairwell pressurisation | Spring-return | Per fire engineering report | BCA/NCC / NFPA 92 | 10–20 N·m |
| Freeze protection valve | Spring-return | Fully open (heating coil) | IMC / ASHRAE 90.1 | 5–20 N·m |
| Economiser outdoor air damper | Spring-return | Fully closed | ASHRAE 90.1 (cold climates) | 10–30 N·m |
| VAV terminal unit damper | Non-spring-return | Fail-in-place (frozen) | General modulating control | 5–10 N·m |
| Cooling-only CHW valve | Non-spring-return | Fail-in-place | General modulating control | 5–15 N·m |
| General exhaust damper | Non-spring-return | Fail-in-place | Non-safety application | 5–20 N·m |
🔑 Key Takeaways
- ✓Spring-return is mandatory for smoke control, freeze protection, and pressurisation safety functions
- ✓Non-spring-return actuators are appropriate for general modulating duty where fail-in-place is safe
- ✓Modern spring-return actuators consume as little as 0.5W holding power — the energy gap has nearly closed
- ✓Always clearly document the required fail position (open or closed) on mechanical schedules for spring-return actuators
- ✓Australian projects must comply with BCA/NCC requirements that align with NFPA and IMC standards for safety-critical actuation