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VENTS NKD 125-1,2-1 A21

Duct heater for supply air post-heating with external control.
Connected air duct diameter – 125 mm.
Heater power – 1.2 kW.

  • Description
  • Characteristics
  • Capacity diagram
  • Downloads
  • Dimensions
  • Designation key
  • Compatibility table
  • Electric heater power selection diagram
  • The heater is designed for integration into a ventilation system and joint operation with an air handling unit equipped with a control system used to switch on the heater and control its operation.
  • The heater maintains the supply duct air temperature at a point set by the unit controller.
  • The casing, the junction box and the heater cover are made of galvanized steel with the heating elements in stainless steel.
  • The heater casing is additionally heatinsulated with 20 mm non-flammable mineral wool layer.
  • The heaters are equipped with rubber seals for airtight connection to the air ducts.
  • The NKD duct heaters are equipped with a power and a signal cable for connection of the heater to the air handling unit controller.
  • The temperature is controlled by a triac power controller by means of switching the full load on and off.
  • Load commutation is carried out by the semiconductor device (triac).
  • The heaters are equipped with overheat thermostats:
    ⏵main overheat protection with automatic reset at +50 °C
    ⏵emergency overheat protection with manual reset at +90 °C
  • The heater design ensures its mounting on the round ducts in any position by means of clamps (included in delivery).
  • The air flow direction shall match the direction of the arrow on the heater casing.
  • The heater is connected to the air handling unit controller using the cable with connectors.
  • In case of horizontal mounting the control box must be installed with the cover upwards.
  • Swivel range from the normal position up to max. 90°.
  • Do not install the control box with the cover downwards.
Parameter NKD 125-1,2-1 A21
Measurement unit
Minimum air capacity 90 m³/h
Current 5.2 A
Power 1200 W
Heating electric reheating -
Duct for round air ducts -
Connection diameter 125 mm
Capacity diagram
Capacity diagram
  • Selection method:
  • Air flow:
  • Pressure:
Operating point
  • Air flow: --
  • Pressure: ---
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"NKD" product description 03-2021 (pdf 429.63Kb)
"NKD" user's manual 11-2020 (V125EN-07) (pdf 1.4Mb)
Download high quality image "NKD" (psd 2.12Mb)
Download image "NKD" for your website (png 285.05Kb)
"Wireless control system A21" user’s manual 09-2022 (V55-8EN-04) (pdf 415.1Kb)
VENTS NKD 125-1,2-1 A21
Parameter Value Measurement unit
∅D 124 mm
B 155 mm
H 251 mm
L 306 mm
L1 190 mm
Designation key
Designation key
Series Connected air duct diameter [mm] - Heater power [kW] - Phases Compatability with automation
NKD 125; 150; 160; 200; 250 0.6; 0.8; 1.2; 1.7; 2.0; 3.0 1: single-phase A21: compatible with A21 automation
Compatibility table
Compatibility table
Heater model (connected air duct diameter)  
NKD 125 A21 VUT/VUE with Ø 125 mm spigot and A21 automation
NKD 150 A21 VUT/VUE with Ø 150 mm spigot and A21 automation
NKD 160 A21 VUT/VUE with Ø 160 mm spigot and A21 automation
NKD 200 A21 VUT/VUE with Ø 200 mm spigot and A21 automation
NKD 250 А21 VUT/VUE with Ø 250 mm spigot and A21 automation
Electric heater power selection diagram
Electric heater power selection diagram

The NKD heater parameters calculation example:

  • It is necessary to select a heater for supply air post-heating to a temperature of +24 °C, provided the temperature downstream of the heat exchanger is +17 °C. Therefore, it is essential to increase temperature by 7 °C. The ventilation system incorporates the VENTS VUT 350 VB EC A21 air handling unit. The rated air flow is 400 m³/h. Determine the intersection of the post-heating temperature line (+7 °C) and the rated air flow line (400 m³/h).
  • In this case the 1200 W heater capacity provides necessary post-heating (+7 °C). The heater NKD 160-1.2-1 with the diameter matching the spigot diameter of the VUT 350 VB EC A21 air handling unit is a suitable model.
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