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Blauberg WKH 50x25-2

Duct water heater for rectangular ducts.
EAN codeEAN4058448032776
  • Description
  • Characteristics
  • Downloads
  • Designation key
  • Dimensions
  • Air pressure loss
  • Calculation diagram

For warming up of supply air in ventilation systems installed in various premises. Suitable for installation in supply or air handling units to warm up the supply air flow. For indoor use only if water serves as a heat carrier. For outdoor Features use antifreezing mixture (ethylene glycol solution). Compatible with 400×200 up to 1000×500 mm rectangular air ducts.


Galvanized steel case. Copper pipe manifold. Heat exchange surface made of aluminium plates. Equipped with a nipple for the system deaeration. Outlet header is equipped with a spigot for installation of an immersion temperature sensor or freezing protection mechanism. Available in two, three- or four-row tube modifications. Suitable for operation at maximum operating pressure 1.6 MPa (16 bar) and maximum transported air temperature +100 °C.


Fixing to rectangular ducts with flange connection. Any mounting position that ensures the heater deaeration. Install a filter upstream to the heater to protect heating elements against dirt ingress. Install the heater in front or behind the fan. In case of mounting behind the fan ensure the distance no less than 1–1.5 m for air flow stabilization and keep the maximum permissible air temperature inside the fan. Connect the heater on counter-flow basis, otherwise its capacity drops by 5–15 %. All the nomographic charts are rated for counter-flow connection. For correct and safe heater operation an automatic control and protection system is recommended, including the following functions:

  • regulation of the heating capacity and temperature of the air heated up;
  • filter clogging control by a differential air pressure sensor;
  • ventilation system start-up with pre-heated heater;
  • use of air dampers with a servo actuator with a return spring;
  • fan turning off in case of the heater freezing danger.

Connection against air flow


Connection along air flow

Parameter WKH 50x25-2 Measurement unit
Number of water coil rows 2 -
Connected air duct size 500х250 mm
Weight 15.8 kg
Casing material galvanized steel -
Air duct for rectangular air ducts -
Documents archieve
Documents archieve
WKH (rectangular) - data sheet (pdf 1012.71Kb)
WKH (rectangular) - user manual (pdf 1.91Mb)
WKH (rectangular) - image (png 751.31Kb)
Designation key
Designation key
Series Flange size (WxH) [cm]   Number of water (glycol) coil rows
WKH 40x20; 50x25; 50x30; 60x30; 60x35; 70x40; 80x50; 90x50; 100x50 2; 3; 4

Model Overall dimensions [mm]
B B1 B2 B3 H H1 H2 H3 L L1 L2 K
WKH 50x25-2 500 520 540 665 250 270 290 200 200 43 43 G 3/4”
Air pressure loss
Air pressure loss

Calculation diagram
Calculation diagram

How to use water heater diagrams. System Parameters: Air flow = 1450 m³/h. Outside air temperature = -15 °C. Water temperature (in/out) = +90/+70 °C. The air flow is 950 m³/h and the air speed in the heater is 3.2 m/s .

To calculate the maximum air temperature find the intersection point of the air flow line with the rated outer temperature shown in blue line (e.g., -15 °C) and draw the line to the left until it crosses the water in/out temperature curve (e.g., +90/+70). From this point draw a vertical line to the supply air temperature downstream of the heater (+24 °C) . To calculate the heater power find the intersection point of the air flow with the rated winter temperature shown in red line (e.g., -15 °C) and draw the line to the right until it crosses the water in/out temperature curve (e.g., +90/+70). From this point draw a vertical line to the heater power axis (21.5 kW) .   To calculate the required water flow in the heater prolong this line downwards to the water flow axis (0.27 l/s). To calculate the water pressure drop in the heater find the intersection point of the line with the pressure loss curve and prolong the line to the right on the water pressure drop axis (3.2 kPa).