Electric heater relays control high-current heating elements from low-voltage thermostats and protect systems from overloads. This guide compares reliable relay types and replacement boards to help you choose the right component for furnaces, baseboard heaters, electric furnaces, hot tubs, and other electric heating applications.
| Product | Primary Use | Key Feature |
|---|---|---|
| Honeywell R841C1227/U Electric Heater Relay | Residential Furnace/Heater Sequencing | Each Relay Switches Up To 5,000 W |
| Emerson 24A34-3 Electric Heat Sequencer | Fan/Heat Sequencing In HVAC Units | Two Switches, 1–20 Second On Timings |
| Aube RC840T-240 Relay With 24V Transformer | Direct Replacement For Relays Using 24V Thermostats | Built-In 24 V Transformer |
| ZGLEDUN Thermal Overload Relay 37–50A | Motor/Heater Overload Protection | Phase Break, Manual/Auto Reset |
| 4 PCS 5-Pin 40A Waterproof Relays (ecocstm) | High-Current Switching For Fans, Heaters, Motors | IP67 Waterproof, 40A Capacity |
Content Navigation
- Honeywell R841C1227/U Electric Heater Relay
- Emerson 24A34-3 Electric Heat Sequencer, 2 Switches
- Aube RC840T-240 On/Off Electric Heating Relay With 24V Transformer
- ZGLEDUN Thermal Overload Relay 37–50A For Motor And Heater Protection
- 4 PCS 5-Pin 40A Waterproof Relays (ecocstm)
- Buying Guide: How To Choose The Right Electric Heater Relay
Honeywell R841C1227/U Electric Heater Relay
The Honeywell R841C1227/U is designed for multi-stage electric heater control and sequencing in residential HVAC systems. It is commonly used where thermostats cycle the heating elements several times per hour.
- Operate With Each Cycle Of The Thermostat: Rated to operate with typical thermostat cycling (4–6 cycles/hour), which helps prevent excessive wear in applications with frequent on/off events.
- High Load Capacity: Each relay can switch up to a 5,000 W load, suitable for many baseboard, strip, and convective electric heating elements.
- Contact Timing: Contacts make and break in about 75 seconds, which can assist in staged element sequencing and reduce inrush stress.
Application notes: This relay suits electric furnaces and sequencers where per-stage wattage is within its rating. Check compatibility with your heater’s control terminals and mounting form factor before replacement.
Emerson 24A34-3 Electric Heat Sequencer, 2 Switches
The Emerson 24A34-3 is a compact sequencer module with two switching elements intended for fan/heat sequencing and staged heater control in HVAC systems.
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- Direct Replacement: Designed as a direct replacement for many fan/heat sequencing functions, making it useful for repairs and retrofits.
- Two Switches: Contains two switching contacts for controlling multiple heating stages or combining fan control with heat stages.
- On Timings: Typical on-timings are 1–20 seconds, enabling short delays for element sequencing and reducing simultaneous inrush current.
Use cases: Best for systems that require simple staged turn-on behavior. Verify the terminal layout and timing characteristics against your original sequencer for proper function.
Aube RC840T-240 On/Off Electric Heating Relay With 24V Transformer
The Aube RC840T-240 combines an electric heating relay with a built-in 24 V transformer, simplifying installation where a low-voltage thermostat controls a high-voltage heating element.
- Direct Replacement: Marketed as a direct replacement for many brand relays, easing retrofit installations.
- Built-In 24 V Transformer: Integrates a transformer for easy connection to 24V thermostats without separate power transformers.
- Thermostat Compatibility: Works with 24V thermostats using 2-wire (R,W) or 3-wire (R,W,C) setups, broadening compatibility.
Installation tip: The built-in transformer simplifies wiring for low-voltage controls. Confirm coil ratings and load capacity match your heater element specifications before installing.
ZGLEDUN Thermal Overload Relay 37–50A For Motor And Heater Protection
The ZGLEDUN thermal overload relay is a protective device intended to safeguard motors and high-current heating circuits from sustained overcurrent and phase faults.
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- Rated Current Range: Adjustable range of 37–50A, suitable for larger heaters or motor-driven heater assemblies.
- Rated Insulation Voltage: Designed for circuits at 50–60Hz with rated insulation voltage up to 690V, supporting higher-voltage systems.
- Protection Functions: Provides phase break protection, manual and automatic reset options, temperature compensation, trip indication, and test/stop buttons for diagnostics.
When to choose: Select thermal overload relays when you need overload and phase-loss protection in addition to switching, especially for motors that power blowers or pump-heater combos.
4 PCS 5-Pin 40A Waterproof Relays (ecocstm)
This pack of four 5-pin relays offers versatile, waterproof switching suitable for automotive or outdoor heater control applications requiring robust environmental protection.
- Material And Construction: Housings made of PA66 flame-retardant material with copper-wound coils for improved heat dissipation and conductivity.
- Waterproofing: IP67-rated sealing provides dust and water resistance, useful for exterior heater controls or damp environments.
- Relay Specs: Model JD1914-12V-40A, five-pin design, coil resistance ~90Ω, coil power ~1.8W, rated for 40A switching loads.
Suitability: Choose these when a compact, sealed relay is needed for switching resistive heating loads or fans in challenging environments. Confirm coil voltage and wiring pinout match the control circuit.
Buying Guide: How To Choose The Right Electric Heater Relay
Selecting the correct relay or protection device requires assessing electrical, mechanical, and environmental parameters. The following considerations help narrow choices effectively.
Load Capacity And Type
Determine Continuous And Inrush Currents: Heating elements have steady resistive currents; motors or fan-assisted heaters can introduce inrush. Choose relays/overload devices with ratings higher than steady-state and capable of handling inrush or use sequencers to stagger starts.
Voltage And Phase Compatibility
Match Voltage And Phase: Confirm relay contact ratings for the system voltage (120V, 240V, higher) and single- or three-phase operation. Overload relays should match motor phase configuration and supply characteristics.
Coil Voltage And Control Signal
Verify Coil And Thermostat Voltage: Common coil voltages include 12V, 24V, and 120/240V. For modern thermostats, 24V coil-compatible relays or relays with built-in transformers (like the Aube RC840T-240) simplify wiring.
Protection Features
Overload And Phase Loss Protection: Thermal overload relays provide motor/heater protection, adjustable trip ranges, and reset modes. Consider these when protecting motors, pumps, or costly heater elements.
Sequencing And Timing
Staged Turn-On To Reduce Inrush: Sequencers and relays with built-in timing (like Emerson sequencers or Honeywell staging relays) help avoid high simultaneous current by delaying element engagement.
Environment And Durability
Ingress Protection And Materials: For outdoor or damp installations select IP-rated relays (IP67) or sealed housings. Flame-retardant materials and high-temperature coil construction help in hot enclosures.
Form Factor And Mounting
Physical Fit And Terminal Layout: Replacement relays should match the mounting holes and terminal orientation of the original device when retrofitting. PCB-mounted, screw terminal, or plug-in types require different mounting considerations.
Control Complexity
Single Stage Vs. Multi-Stage Control: Single pole relays suit simple on/off loads. Multi-stage systems benefit from sequencers or multiple relays to manage staged heating elements and fans.
Installation And Wiring
Ease Of Installation: Products with built-in transformers or clear wiring diagrams reduce installation complexity. Ensure proper fusing and wire gauge to match relay contact ratings and load currents.
Safety And Standards
Certification And Derating: Look for relays meeting relevant safety standards and consider derating for continuous duty at elevated ambient temperatures. Use properly rated disconnects and thermal protection where required.
Comparison Perspectives
- High-Capacity Switching: Choose heavy-duty relays or thermal overloads (ZGLEDUN) for large heater banks and motor-associated loads.
- Simplified Thermostat Integration: Use relays with built-in transformers (Aube RC840T-240) for direct 24V thermostat control without an external transformer.
- Sequencing Needs: Install sequencers (Emerson or Honeywell sequencing relays) to stagger stages, reduce peak demand, and extend contact life.
- Harsh Environments: Opt for waterproof, sealed relays (ecocstm 40A IP67) where moisture or dust exposure is likely.
- Replacement Boards: For specialty systems (e.g., spa or OEM heater controllers), use dedicated replacement boards matched to the original part number.
Final selection should align relay ratings, control voltage, protective features, and environmental resilience with the specific heater or HVAC application. When in doubt, consult equipment wiring diagrams and an HVAC or electrical professional to confirm compatibility and compliance with local codes.
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