Belimo LM24A-SR – the 24V Modulating Damper Actuator for Precise HVAC Control

July 30 2025 , 5 min reading time

The Belimo LM24A-SR is a 24 V modulating damper actuator that delivers 5 Nm of torque with quiet, 1 W energy-saving operation. Built for VAV boxes, zone dampers and compact AHUs, it offers 2–10 V control, manual override and IP54 protection. Contractors value its five-minute installation and maintenance-free design, while facilities teams enjoy precise airflow control that reduces fan energy and enhances comfort.

Belimo LM24A-SR – Buy the 24 V Modulating Damper Actuator for Precise HVAC Control

Belimo LM24A-SR – 24 V Modulating Damper Actuator Built for Reliable HVAC Performance

Why Choose the Belimo LM24A-SR?

The Belimo LM24A-SR is a compact, 5 Nm modulating damper actuator that brings seamless 0–10 V positioning and feedback to air-side HVAC control. With a 24 V AC/DC supply, IP54 housing and ultra-low 1 W running load, it delivers the accuracy consultants demand while keeping running costs to an absolute minimum. Whether you are upgrading a variable air-volume (VAV) box or fitting out a packaged air-handling unit, the LM24A-SR provides the dependable movement every modern building needs.

Key Technical Specifications

Torque: 5 Nm – ideal for dampers up to approximately 1 m²
Nominal voltage: 24 V AC/DC (range 19.2–28.8 V)
Control signal: Modulating 2…10 V DC, 100 kΩ input impedance
Position feedback: 2…10 V DC, max. 1 mA
Running time: 150 s for 90° rotation
Sound power level: 35 dB(A) – quieter than an office conversation
Ingress protection: IP54 / NEMA 2
Ambient range: −30 °C to +50 °C, 95 % RH non-condensing
Manual override: Push-button with lock, plus universal shaft clamp 6–20 mm
Power draw for sizing: 2 VA – simplifies transformer calculations

Real-World Applications That Unlock Value

1. VAV Terminal Units in Open-Plan Offices

Open spaces demand tight airflow control to stay comfortable across changing occupancies. When paired with pressure-independent VAV boxes, the LM24A-SR maintains exact damper positions, ensuring the required litres-per-second while minimising fan energy. The 2–10 V feedback allows the building-management system (BMS) to verify every stroke in real time, supporting smart analytics and early fault detection.

2. Zone Dampers in Multi-Residential Developments

In apartment blocks using centralised ventilation, each flat often has a fire-rated volume control damper. The LM24A-SR’s slim 0.47 kg body and 150 s stroke keep acoustic breakthrough to a whisper, solving complaints about ‘motor noise’ radiating through ductwork. Maintenance teams appreciate the actuator’s sealed gearbox and overload protection, meaning no routine servicing.

3. Packaged Air-Handling Units and Heat Recovery Ventilators

OEMs frequently pre-install the Belimo LM24A-SR on fresh-air and exhaust dampers inside small rooftop or wall-mounted AHUs. Because the actuator draws only 1 W once in motion and 0.4 W at rest, it reduces the panel VA budget and keeps cabinet temperatures low – crucial when electronics share the enclosure.

Five Benefits That Boost Return on Investment

Energy Efficiency From Day One

The LM24A-SR’s high 100 kΩ input impedance places a negligible load on the controller output, while the 1 W power draw translates to roughly 8.8 kWh per year – less than one LED lamp. Over thousands of actuators in a campus, the utility savings add up quickly.

Precision Airflow Equals Better Comfort

With ±5 % position accuracy and smooth proportional control, temperature swings are reduced, and occupants remain comfortable without unnecessary reheats or chill cycles.

Quieter Spaces, Happier People

At just 35 dB(A) the actuator moves silently, meeting WELL Building and BCO acoustic guidelines for open-plan workspaces.

Fast, Tool-Light Installation

The universal shaft clamp fits 6–20 mm spindles, secured with a single screw. An anti-rotation bracket is supplied in the box, so engineers are not forced to fabricate straps on site. Push the manual override, set the blade angle, lock and power up – job done in under five minutes.

Zero Scheduled Maintenance

Belimo engineers designed the drive train for lifelong lubrication and stall protection. Once fitted, no periodic greasing or recalibration is required, freeing facilities teams for higher-value tasks.

Compatible Accessories

Need auxiliary proof of position for safety circuits? Simply clip on an S2A SPDT switch pack. For analogue master–slave control, add the Z-UIC signal converter to translate 0–10 V to 4–20 mA or vice-versa. Optional form-fit inserts adapt the clamp to 8 mm, 10 mm or 12 mm square shafts for legacy dampers.

Installation and Wiring Guide

Confirm damper torque ≤ 5 Nm across the full stroke.
Mount the LM24A-SR on the spindle and tighten the clamp to 10 Nm.
Fit the anti-rotation bracket into a handy fixing point.
Wire 24 V supply – black (−) and red (+); connect white (Y) for control and orange (U) for feedback.
Size the transformer at 2 VA per actuator or apply diversity where appropriate.
Commission via BMS graphics, checking 0 %, 50 % and 100 % positions.

Frequently Asked Questions

Is the LM24A-SR suitable for outside installation?

Yes, provided it is shielded from direct rain, salt spray and solar radiation, and ambient conditions stay within −30 °C to +50 °C with humidity below 95 % RH.

Can I drive several actuators from one controller output?

Absolutely – parallel wiring is supported. Just ensure the combined in-rush and running currents stay within the power supply limits.

Does it need limit switches?

No. The actuator is overload protected and stops automatically on reaching each end stop.

How loud is 35 dB(A) in practice?

About the same as a quiet library. In most ducted installations, the sound cannot be heard beyond the grille.

Order Today – Delivered Tomorrow

We hold Belimo LM24A-SR actuators in stock for next-day delivery across the UK. Every unit ships with a two-year manufacturer’s warranty and our technical team is on hand for pre-sale sizing or commissioning advice. Click Add to Basket now or call 01772 284 626 for volume pricing.