Vents Air duct heater NK 250 (Ø250MM/2.4 KW/IP40)

An electric duct heater for round 250 mm ducting, 2.4 kW in two 1.2 kW elements. Requires a minimum airflow of 265 m³/h.

The NK 250 has the same power as the 160 and 200 mm versions but asks for considerably more air: 265 against 180 m³/h. That difference is worth understanding before you choose.

Same power, more air required

It looks contradictory: a larger duct, the same power, and yet a higher demand on airflow. It makes sense once you look at what the requirement protects.

The minimum exists to carry heat away from the element. What counts for that is not only how much air passes per hour, but how fast that air moves across the element. In a 250 mm duct the flow area is far larger than in a 160 mm one, so the same quantity of air per hour travels more slowly there.

Slower air removes heat less effectively. To keep the same cooling at the element, more air per hour has to pass: hence 265 rather than 180 m³/h.

In practice that means the largest size is not automatically the safest choice. Pick the size that matches your ducting, then check that your fan reaches the corresponding minimum with filter and ducting included. A fan rated 300 m³/h that retains 250 behind a full carbon filter falls short here.

Work out the temperature rise as well. At 2.4 kW and 265 m³/h you land at roughly 27 degrees; if you need more air, that rise gets smaller.

Connection

10.4 amps on 230 volts, single phase, wired in by a qualified electrician following the Vents manual. The heater goes into 250 mm ducting, horizontal or vertical, and must never operate without the fan running. Keep the connection end accessible for resetting the protection.

Technical Specifications:

• Duct: 250 mm
• Power: 2.4 kW, two 1.2 kW elements
• Minimum airflow: 265 m³/h
• Current: 10.4 A
• Supply: 230 V / 50 Hz, single phase
• Ingress protection: IP40
• Weight: 3.2 kg

Frequently asked questions

Why does the largest size need the most air?
Because air in a wider duct moves more slowly and therefore carries heat away from the element less effectively.

Will my fan reach 265 m³/h?
Work from what survives with filter and ducting attached, not from the number on the box.

How much warmer does the air get?
At 265 m³/h, roughly 27 degrees, as an approximation without duct losses.

Is a larger size safer?
No. Pick the size matching your ducting and check you meet its airflow minimum.