On All Quantum models, the right hand side is occupied by the electronics, not elements & bricks. Therefore the right side will always feel cooler to the touch.

On the QM125, the outer case is the same size as the QM150, but internally the core is smaller, with one column less of bricks and shorter elements. Therefore the left hand side will feel cooler than the middle of the heater. This is normal!

Judge the heater by how warm the ROOM feels, not how warm the case of the heater feels.

The Quantum is designed to distribute heat using the fan not radiate like a convention radiator or panel heater.