There are a few types of tubular heaters with different power ranges to each.

 

Screw-in tubular heaters with threaded plug for heating liquids.
Power range from 1000 W  to 12000 W
  (Standard applications include the heating of recycled water for sanitary services, chlorinated water, demineralized water, fuel oil, mineral oil on the basis of the specific load)

Screw-in tubular heaters are electro-thermal sets equipped with threaded plugs to heat up liquids.
Power applications range from 2000 W  to  35000 W  

Screw-in tubular heaters with threaded plug for heating liquids.
Power range from 1000 W  to 6000 W