A hydronic auxiliary electric heater supplies supplementary resistance heat to a circulating water or compatible water-glycol loop used for space heating.
A hydronic auxiliary electric heater supplies supplementary resistance heat to a circulating water or compatible water-glycol loop used for space heating. It can support an air-to-water heat pump or another primary heat source under defined operating conditions. Selection starts with the required extra heat at the system design point, then considers flow, pressure, fluid composition and controls. The assembly is part of the water side of HVAC equipment. Its function is distinct from heating ventilation air directly and from maintaining the temperature of domestic hot-water distribution pipes.
Build the specification around the heat shortfall, circulating fluid and control sequence, including how the auxiliary heater cooperates with the primary heat source.
For a hydronic system that needs additional output under specific conditions. Define the heat-pump contribution and remaining load at the same outdoor and water temperatures before assigning auxiliary capacity.
Enquire about this configurationFor adding heat to a central heating-water circuit. State the supply and return requirements, connected emitters and hydraulic arrangement so the heater specification follows the actual system duty.
Enquire about this configurationFor a system sequence that calls for electrical assistance during warm-up. Specify the initial fluid temperature, permitted warm-up profile and the conditions for handing control back to the main source.
Enquire about this configurationDiscuss the heater location using the complete circuit diagram, including pumps, buffer vessels, bypasses and zone valves. Confirm which operating states preserve the required circulation.
Compare the auxiliary load profile with electrical capacity and the system's permitted temperature variation. The requested heat should reflect the shortfall under defined conditions rather than an arbitrary replacement for the main source.
Define when supplemental heat becomes available and how it reduces as the primary source recovers. Agree the sensor locations and controller responsibilities to avoid conflicting temperature demands.
Review wetted materials against water treatment and glycol data. Include isolation and service access in the equipment layout, with provisions established by the system designer.
Share these details with your inquiry. Product ratings and operating limits are confirmed for the selected configuration.
| What to specify | Unit / format | Selection guidance |
|---|---|---|
| Supplemental heating duty | kW | Provide the required extra capacity and the conditions at which the main source cannot meet the load. |
| Water temperatures | °C | State design supply, return, cold-start and maximum permitted temperatures. |
| Circulating flow | L/min / m³/h | Give normal and minimum flow and describe changes caused by pumps, valves or operating zones. |
| Fluid composition | % / fluid grade | Identify water treatment and glycol type and concentration, where used, rather than stating only antifreeze. |
| Hydraulic conditions | bar / kPa | Supply working and design pressure plus the pressure-drop allowance for the heater assembly. |
| Connections and access | mm / connection standard | Show pipe connections, orientation, service clearances and the intended position in the hydraulic circuit. |
| Electrical capacity | V / Hz / phase / kW | Define the available supply and any demand limit that restricts auxiliary-heater operation. |
| Enable and regulation signals | signal / sequence | Describe the controller's heat request, flow proof, temperature feedback and fault-handling responsibilities. |
Provide the required extra capacity and the conditions at which the main source cannot meet the load.
State design supply, return, cold-start and maximum permitted temperatures.
Give normal and minimum flow and describe changes caused by pumps, valves or operating zones.
Identify water treatment and glycol type and concentration, where used, rather than stating only antifreeze.
Supply working and design pressure plus the pressure-drop allowance for the heater assembly.
Show pipe connections, orientation, service clearances and the intended position in the hydraulic circuit.
Define the available supply and any demand limit that restricts auxiliary-heater operation.
Describe the controller's heat request, flow proof, temperature feedback and fault-handling responsibilities.
For a documented heating shortfall at particular operating conditions. Selection should use the heat-pump output and building demand at matching temperatures, together with the planned auxiliary control sequence.
For supplemental heat in an HVAC water circuit serving suitable emitters. Identify the required flow and temperature profile across the connected loads instead of relying on nominal equipment size.
For cold-start assistance where the plant design calls for it. Specify the fluid mass, starting condition and sequence, with circulation established before electrical heating is enabled.
Use the building load and primary-source output at the same design condition. Distinguish supplementary operation from full emergency backup, because they can require different electrical capacities and control strategies.
Evaluate the fluid, flow range, pressure allowance and available pump head. Review all relevant valve positions and pump modes, including situations where only a small heating zone remains active.
Specify heat enable, staging or modulation, circulation proof and independent overtemperature protection. Define what the system does after a fault instead of relying on a single temperature demand signal.
Send your application details, drawing and planned quantity. We can review the configuration and the information needed for a quotation.
These references explain heating principles. Confirm the ratings, approvals and operating limits of the proposed VELHEAT configuration in its own documentation.
Inline supplemental electric heating for air-to-water hydronic heat pumps and coordination with the primary source; no proprietary ratings or performance claims adopted.
